Symposium Organizers
Alexei Gruverman University of Nebraska-Lincoln
Craig J. Fennie Cornell University
Iwao Kunishima Toshiba Corporation
Beatriz Noheda University of Groningen
Tae Won Noh Seoul National University
F1: Interfaces and Heterostructures
Session Chairs
Tae Won Noh
Darrell Schlom
Monday PM, November 30, 2009
Grand Ballroom (Sheraton)
9:00 AM - **F1.1
Understanding and Exploiting the Interface Between Ferroelectrics/Multiferroics and Metal Electrodes.
Nicola Spaldin 1
1 , UC Santa Barbara, Santa Barbara, California, United States
Show AbstractThe behavior of ferroelectrics and multiferroics in practical devices is strongly influenced by the physics of the dielectric -- metal interface and its response to an applied electric field. Here we explain how recent developments in density functional theory methodology now permit fully first-principles calculations of the metal -- dielectric interface under well-defined electrical boundary conditions. These new tools allow explicit calculation of the effects of interface chemistry, finite metallic screening length, structural and point defects, etc. on the functional properties such as polarization, dielectric response and piezoelectricity. We show how the new techniques have been used to answer a number of important and long-standing questions in the behavior of ferroelectric and dielectric devices, including the origin of the so-called dielectric dead layer in nanoscale capacitors, and the effects responsible for the destabilization of the ferroelectric state in thin films. We propose a novel mechanism of interfacial ferroelectricity that suggests a route to thin-film ferroelectric devices that are free of deleterious size effects.Work done in collaboration with Massimiliano Stengel and David Vanderbilt.
9:30 AM - **F1.2
Ferroelectric Tunnel Junctions.
Evgeny Tsymbal 1
1 Department of Physics and Astronomy, University of Nebraska, Lincoln, Nebraska, United States
Show AbstractTunnel junctions are electronic devices representing two metal electrodes separated by a very thin insulating barrier layer, where electrons can quantum-mechanically be transmitted across the potential barrier that exceeds electron’s energy. So far almost all the existing tunnel junctions were based on non-polar dielectrics. An exciting possibility to extend the functionality of tunnel junctions is to use a ferroelectric insulator as a barrier to make a ferroelectric tunnel junction (FTJ). [1,2] The key property of a FTJ is the tunneling electroresistance (TER) effect that is a change in the electrical resistance of a FTJ with reversal of ferroelectric polarization. One of the mechanisms responsible for this effect is the incomplete screening of polarization charges which makes the depolarizing field and hence the potential profile seen by transport electrons different for opposite polarization orientations. [1] Another mechanism originates from the polarization-switching-induced changes in ionic positions near the interfaces which affect the atomic orbital hybridizations at the interface and hence alter the transmission probability. [3] Finally, the polarization reversal may change the decay constant of the evanescent states in the barrier due to different magnitude of ferroelectric displacements for the opposite polarization orientations. [4]Functional properties of a FTJ can be extended by replacing normal metal electrodes by ferromagnets. In such a multiferroic tunnel junction (MFTJ) spin-dependent tunneling may be controlled by the electric polarization of the ferroelectric barrier. [2,4,5] This implies that by switching the ferroelectric polarization one can affect the tunneling magnetoresistance (TMR). MFTJs represent therefore multifunctional four-state resistance devices that can be controlled both by electric and magnetic fields due to the coexistence of TER and TMR effects. This talk will address the physics of FTJs and MFTJs based on our recent model and first-principles calculations. In particular, we will discuss the effect of a thin non-polar dielectric layer at the FTJ interface that leads to significantly enhanced values TER. This effect may be relevant to recent experimental results showing that the resistance of a FTJ can be changed by many orders of magnitude at the coercive electric field of the ferroelectric barrier. 1. M. Y. Zhuravlev, R. F. Sabirianov, S. S. Jaswal, and E. Y. Tsymbal, Phys. Rev. Lett. 94, 246802 (2005).2. E. Y. Tsymbal and H. Kohlstedt, Science 313, 181 (2006).3. J. P. Velev, C.-G. Duan, K. D. Belashchenko, S. S. Jaswal, and E. Y. Tsymbal, Phys. Rev. Lett. 98, 137201 (2007). 4. J. P. Velev, C.-G. Duan, J. D. Burton, A. Smogunov, M. K. Niranjan, E. Tosatti, S. S. Jaswal, and E. Y. Tsymbal, Nano Letters 9, 427 (2009).5. M. Y. Zhuravlev, S. S. Jaswal, E.Y. Tsymbal, and R. F. Sabirianov, Appl. Phys. Lett. 87, 222114 (2005).
10:00 AM - F1.3
Engineering Ferroelectricity in the Epitaxial Si/SrTiO$_3$ System.
Alexie Kolpak 1 , Fred Walker 1 , James Reiner 1 , Charles Ahn 1 , Sohrab Ismail-Beigi 1
1 Center for Research on Interface Structures and Phenomena (CRISP), Yale University, New Haven, Connecticut, United States
Show AbstractOne of the current challenges in materials science is the developmentof new devices such as ferroelectric field effect transistors (FETs)that integrate functional oxides with silicon. Recent reports of aswitchable polarization in very thin SrTiO$_3$ films on silicon makesthe Si/SrTiO$_3$ system a promising candidate for ferroelectric FETs.Using density functional theory, however, we demonstrate that theepitaxial Si/SrTiO$_3$ interface is characterized by a pinned,unswitchable interface polarization and an interface dipole whichbiases the system towards a positively poled ground state, whichinhibits ferroelectric switching between monodomain states.Furthermore, we show that a significant interface density of states isrequired to stabilize a polarization across the entire SrTiO$_3$ film.As a result of these intrinsic interface properties, epitaxialSrTiO$_3$ films are electronically decoupled from the siliconsubstrate. However, based on our understanding of the propertieswhich govern the behavior of the Si/SrTiO$_3$ system, we proposespecific design principles, in terms of structural and electronicproperties, for the development of an electronically coupled interfacebetween a complex oxide and silicon; we also give a concrete exampleof such an interface.
10:15 AM - F1.4
Atomic-level Mapping of SrTiO3 on Si (001) using X-ray Direct Methods.
Christian Schlepuetz 1 , Naji Husseini 1 , Divine Kumah 1 , Roy Clarke 1 , Yizhak Yacoby 2 , Philip Willmott 3 , Matts Bjoerck 3 , Stephan Pauli 3 , Maitri Warusawithana 4 , Darrell Schlom 4
1 Physics Department, University of Michigan, Ann Arbor, Michigan, United States, 2 Physics Department, Hebrew University, Jerusalem, 91904, Israel, 3 Swiss Light Source, Paul Scherrer Institut, Villigen, 5232, Switzerland, 4 Materials Science and Engineering, Cornell University, Ithaca, Michigan, United States
Show AbstractAtomic-scale resolution is essential to the study of the three-dimensional structure of epitaxial thin films. The subtle structural displacements and distortions, often at the sub-Angstrom level, that accompany ferroic behavior in perovskite systems present special challenges that can only be addressed quantitatively using x-ray direct methods. Here, we describe new surface x-ray diffraction results on SrTiO3 layers grown epitaxially on Si (001) wafers. In this novel epitaxial oxide-on-semiconductor system, the SrTiO3 was reported to exhibit ferroelectric nanodomains at temperatures well above ambient [1]. Synchrotron x-ray radiation measurements, obtained at the Swiss Light Source and Advanced Photon Source and analyzed with phase-retrieval methods, determined quantitatively the atomic structure and lattice spacings as a function of position relative to the substrate interface. The epitaxial strain is crucial to explaining the stabilization of a spontaneously polarized state of SrTiO3, which is not present in the bulk material. An in-plane 45° rotation of the film relative to the silicon substrate, together with a ~1.7 % compressive strain, brings the SrTiO3 into approximate registry with the substrate [1]. We confirmed that 5 unit cells of SrTiO3 on Si exhibit good epitaxial registry, whereas thicker samples (up to 10 unit cells) are partially relaxed. The resonant response of the complex x-ray scattering factor, measured by tuning the x-ray energy to the absorption K-edge of Sr, is used to deconvolute the effects of interface roughness, chemical mixing and strain. Control of the structure at the Si-SrTiO3 interface will be essential for engineering ferroelectric-semiconductor hybrid devices. [1] Maitri P. Warusawithana, et al. Science 324, 367 (2009). *Current address: Department of Physics, Florida State University, Tallahassee, FL 32306
10:30 AM - F1: Interface
Break
10:45 AM - **F1.5
Tuning the Properties of PbTiO3/SrTiO3 Superlattices.
Pavlo Zubko 1 , Nicolas Stucki 1 , Celine Lichtensteiger 1 , Stefano Gariglio 1 , Jean-Marc Triscone 1 , Matthew Dawber 2 , Eric Bousquet 3 , Patrick Hermet 3 , Philippe Ghosez 3
1 Department of Condensed Matter Physics, University of Geneva, Geneva Switzerland, 2 Department of Physics and Astronomy, Stony Brook University, Stony Brook, New York, United States, 3 Physique Theoretique des Materiaux, University of Liege, Liege Belgium
Show AbstractPbTiO3/SrTiO3 superlattices have proven to be an exciting system, both as a way of creating new artificial materials with desirable properties, as well as for their interesting new physics. Both parent compounds have been extensively studied for decades, and with the tiny lattice parameter mismatch between them, it would seem that the PbTiO3/SrTiO3 structure could be the archetype of ferroelectric/paraelectric superlattices. Indeed, over most of the compositional range, the structural and electrical properties can be well described by a simple Landau-theory-based electrostatic model with bulk PbTiO3 and SrTiO3 parameters from the literature, but even this simple two-component structure is more interesting than may at first appear. As the individual layers get thinner and the number of interfaces increases, the properties of the interfaces themselves become important. Experimentally, a recovery of ferroelectricity is observed for compositions which are expected to be paraelectric. Theoretically, ab initio calculations show that local symmetry breaking at the interfaces allows the unusual coupling between oxygen octahedral rotations and the polar mode leading to improper ferroelectricity. Recently, we have observed ordered nanodomains using x-ray diffraction, similar to those seen in ultrathin PbTiO3 films. Stripe domains are known to scale with the thickness of the ferroelectric. Superlattices, however, offer the possibility of controlling domain sizes independently of the total thickness of the structure, enabling large and highly tuneable permittivities to be attained. Moreover, the large resistances of the thick samples allow voltages to be applied to large area electrodes, enabling the response of nanodomains to electric fields to be studied simultaneously with x-rays and electrical measurements. With recent discoveries that domain walls can possess very interesting properties that add new functionality to the host materials, PbTiO3/SrTiO3 superlattices are an ideal system for studying domains at the nanoscale and realising the concepts of nanodomain engineering.
11:15 AM - **F1.6
Synchrotron X-ray Probe for Structural Evolution of Ferroelectric Heterostructure Thin Films.
Ji Young Jo 1 , Rebecca Sichel 1 , Ho Nyung Lee 2 , Serge Nakhmanson 3 , Eric Dufresne 4 , Paul Evans 1
1 Materials Science and Engineering and Materials Science Program, University of Wisconsin-Madison, Madison, Wisconsin, United States, 2 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 3 , Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States, 4 , Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractThe nanoscale structural evolution of epitaxial thin film heterostructures can be used to probe the novel properties that are available through structural confinement. In a multilayer consisting of ferroelectric and dielectric components, bound charges at interfaces arising from the ferroelectric component’s spontaneous polarization generate an electric field opposite to the polarization. The system tends to reduce the energy associated with bound charges by developing a static polarization in the dielectric component even at external electric field of zero. An important outstanding question is what role this polarization has in the properties of the heterostructure. In typical ferroelectrics, for example, the polarization leads to a piezoelectric response to applied electric field. We present x-ray diffraction studies of a ferroelectric/dielectric BaTiO3/CaTiO3multilayer, from which we deduce the contributions of individual components of the heterostructure to the overall piezoelectric response. We compare our experimental results to predictions of the local polarization and piezoelectric distortion based on density functional theory calculations.Time-resolved x-ray microdiffraction allowed us to probe the structural response of a multilayer with ferroelectric and dielectric components to external electric fields. The intensity of satellite x-ray reflections in ferroelectric/dielectric multilayers is sensitive to the lattice constants of the component layers. The variation of this intensity as a function of the electric field can be used to resolve piezoelectric responses of individual component layers. A piezoelectric response is observed in both ferroelectric and dielectric components, suggesting equal polarization through the entire multilayer. Density functional theory calculations of a model multilayer consisting of 4 unit cells of ferroelectric BaTiO3 and 2 unit cells of non-ferroelectric CaTiO3 in each period predict equal remnant polarization in both layers.
11:45 AM - F1.7
Polarization-dependent Electron Tunneling into Ferroelectric Surfaces.
Peter Maksymovych 1 , Stephen Jesse 1 , Pu Yu 2 , Ramamoorthy Ramesh 2 , Arthur Baddorf 1 , Sergei Kalinin 1
1 Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Department of Physics and Department of Materials Science, University of California, Berkeley , California, United States
Show AbstractElectron tunneling underlies numerous devices relevant to information technology and has been proposed in future energy harvesting and quantum computing applications. Replacing a conventional insulator in the tunnel junction with an electronically correlated material can yield new types of electronic functionality. In one such concept, dubbed ferroelectric tunneling, the tunneling barrier height is controlled by the polarization of a ferroelectric oxide, enabling non-volatile conduction states that can be switched with electric field. The key challenge of ferroelectric tunneling is to find a material system that simultaneously satisfies the dimensional constraints for tunneling transport and ferroelectricity, as well as to assure that the conductance is not dominated by extrinsic effects of charge injection and filamentary conduction, which is ubiquitous in complex oxides.In this talk we will demonstrate a highly reproducible polarization control of local electron transport through epitaxial Pb(Zr0.2Ti0.8)O3 films. Despite being 30-50 nm thick, conductive atomic force microscopy revealed that the films possessed spatially and temporally reproducible local conductivity in the regime of Fowler-Nordheim electron tunneling. This is likely due to a strong electric field in the sub-surface region (excess of 1 MV/cm) created by the relatively sharp metal tip. Local I-V characteristics exhibited strong hysteretic behavior across the surface. By combining conducting atomic force microscopy with piezoresponse force microscopy, we have, for the first time, directly correlated local events of ferroelectric and resistive switching [1]. The large spontaneous polarization of PZT produced as strong as 500-fold enhancement of FN-tunneling conductance upon ferroelectric switching, sufficient to demonstrate a local non-volatile memory function. The physical mechanism of the observed effect was traced to the polarization-dependence of the height and possibly width of the metal-ferroelectric Schottky barrier. By observing the role of inherent disorder in ferroelectrics and comparing films grown on different electrode materials, we have shown that the switching voltage and the magnitude of conductance hysteresis are subject to electrostatic control via ferroelectric switching. Variable-temperature measurements and local effects due to dielectric non-linearities will also be discussed.Experiments were done at the Center for Nanophase Materials Sciences, Office of Basic Energy Sciences, U.S. Department of Energy. PM: Research performed as a Eugene P. Wigner Fellow and staff member at the Oak Ridge National Laboratory.[1] P. Maksymovych, S. Jesse, P. Yu, R. Ramesh, A. P. Baddorf, S. V. Kalinin, Science 324 (2009) 1421.
12:00 PM - F1.8
Ferroelectric Polarization in BaTiO3/CaTiO3 Superlattices.
Sung Seok Seo 1 , Ho Nyung Lee 1
1 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractEpitaxial strain is one of important ingredients in ferroelectric heterostructures for enhancing ferroelectric and dielectric properties. For examples, superlattices (SLs) composed of ferroelectric BaTiO3 (BTO) and paraelectric SrTiO3 (STO) layers have previously shown such a great promise. While the basic mechanism responsible for the strong strain-polarization coupling in SLs could be understood by electrostatic interlayer coupling between the ferroelectric and paraelectric layers, recently discovered ‘improper ferroelectricity’ in PbTiO3/STO SLs has shown the importance of understanding on new interfacial behaviors in SL structures.In this work, strain-polarization coupling of new SLs composed of BTO and paraelectric CaTiO3 (CTO) has been studied. When the SLs are grown on STO substrates, the average in-plane lattice parameter of bulk BTO and CTO is very close to that of STO. However, off-specular x-ray diffraction studies show that the averaged lattice-constants of the SLs depend mostly on the sublayer thicknesses. While it has been theoretically found that (BTO)n/(CTO)n SLs reach the highest polarization for the largest value of n by ab initio calculations when perfect lattice-strain is maintained, our experimental results on BTO/CTO SLs show a varying lattice-strain state and systematic reduction in ferroelectric polarization with increasing sublayer thickness. Hence, the strain coupling plays more important role in ferroelectric properties than the electrostatic interlayer coupling based on the constant dielectric permittivity. It is also remarkable that the less relaxed SLs with thin sublayer thicknesses can stabilize the ferroelectric state even better than the SLs with thick sublayer thicknesses. Theoretical models will be discussed in the scheme of the atomic corrugation in CaO layers, which plays an important role in stabilizing the ferroelectric state in the shorter period BTO/CTO SLs.Research sponsored by the Division of Materials Sciences and Engineering, US Department of Energy.
12:15 PM - F1.9
Atomic Layer Controlled Growth and Properties of BaTiO3/SrTiO3 Superlattices Grown by Pulsed Laser Deposition.
Chung Wung Bark 1 , Ho Won Jang 1 , Chad Folkman 1 , Seung Hyub Baek 1 , Jae Wan Park 1 , Chang-Beom Eom 1 , PingPing Wu 2 , Che-Hui (Kevin) Lee 2 , Eftihia Vlahos 2 , Venkatraman Gopalan 2 , Darrell Schlom 2 , Long-Qing Chen 2 , Michael Biegalski 3
1 Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States, 2 Department of Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania, United States, 3 Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractArtificially layered superlattices present remarkably different behaviors from their composite materials. The precise control of the periodicity with atomically sharp interfaces by atomic layer controlled growth allows us to produce theoretically designed superlattice with novel properties which cannot be obtained in a single phase materials. Furthermore, strain engineering by heteroepitaxy is an additional knob to control their novel properties. Theoretical phase field simulation predicts that certain type of (BaTiO3)n/(SrTiO3)n superlattices with a biaxial strain have novel domain wall configurations resulting in extremely high electro-optic coefficients. We have grown a series of high quality (BaTiO3)/(SrTiO3) superlattices with varying perodicities on single crystal conducting SrRuO3 bottom electrodes. Several rare earth scandate substrates (GdScO3, DyScO3, SmScO3) were used to change the strain state of the superlattices. Four-circle x-ray diffraction shows that the BTO/STO superlattices are fully commensurate with the substrates and long-range periodicity was observed. The crystalline quality (measured by FWHM of the 002 peak) of the superlattices is closed to those of the bulk single crystals (FWHM ~ 0.02). Polarization-electric field hysteresis loops were measurements as a function of temperatures indicate that the superlattice had ~10 times smaller coercive field than single phase BaTiO3 thin film and this result is in good agreement with theoretical predictions. We will also discuss the role of domain walls in these superlattices and their potential for device applications.
F2: Coupling in Multiferroics and the Magnetoelectric Effect
Session Chairs
Long-Qing Chen
Nicola Spaldin
Monday PM, November 30, 2009
Grand Ballroom (Sheraton)
2:30 PM - **F2.1
Control of Large Room-temperature Electrical Polarizations with Magnetic Fields: A Three-state Magnetoelectric Memory.
Jim Scott 1 2
1 Physics Department, Cambridge University, Cambridge United Kingdom, 2 Physics Department, University of Puerto Rico, San Juan, Puerto Rico, United States
Show AbstractWe have found that the material PbFe(2/3)W(1/3)O3 mixed with PbZr(x)Ti(1-x)O3 ["PZT"] at 20% PFW/80% PZT produces a tetragonal single-phase crystal that is ferroelectric (spontaneous P = 70 microCoul/sq.cm.) and magnetic. The material is a bi-relaxor, meaning that over a wide temperature range both the electric polarizations P and magnetizations M exhibit short-range order. There is strong coupling of form P-squared M-squared not directly but through strain via electrostriction and magnetostriction, as described theoretically by Pirc, Blinc, and Scott (Phys. Rev. B 2009). At room temperature in the presence of a modest applied magnetic field (H < 0.5 T) the interaction is negative, causing the ferroelectric order to destabilize to a relaxor state [Ashok Kumar, G. Sharma, R. S. Katiyar, et al., J. Phys. Cond. Mat. 2009). This switches P from 70 uC/cm2 to very near zero and reduces dielectric constant from 1200 to 25 -- a very strong magnetically switched capacitance with three-state logic (+P, 0, -P). The polarization relaxation time at 295K varies by a factor of 10,000 with applied magnetic field and satisfies the theoretically predicted field dependence of the Pirc-Blinc theory with a dependence that resembles a Vogel-Fulcher model, but with a critical field H = 0.92 T instead of a critical temperature. This magnetoelectrically switched polarization is x1000 stronger than that reported by Kimura and occurs at room temperature.
3:00 PM - F2.2
Large Strain-Mediated Magnetoelectric Response in Multiferroics.
Jacek Wojdel 1 , Jorge Iniguez 1
1 , Institut de Ciencia de Materials de Barcelona (CSIC), Bellaterra, Barcelona, Spain
Show AbstractWe have performed a first-principles study of the magnetoelectric response of room-temperature multiferroic BiFeO3 (BFO) and related compounds in which iron is substituted by a different magnetic species (e.g., Cr, Co, etc.). We have considered the situation in which the cycloidal spin modulation of BFO is suppressed, as it is believed to occur in BFO thin films and Bi_{1-x}La_{x}FeO3 solid solutions. Our results reveal that, in such conditions, these compounds display a large linear magnetoelectric coupling (up to values of about 50*10^{-4} g.u.) comparable with the biggest ones ever measured. Such a strong coupling is mediated by the structural (inverse piezoelectric) response to an applied electric field, which provides us with a robust mechanism to obtain large magnetoelectric effects at room temperature, especially in thin films suitably grown. We will discuss the generality of the newly found coupling mechanism, and the possibility of observing (or inducing) it in other multiferroics.
3:15 PM - F2.3
Magnetostructural Effect in the Multiferroic BiFeO3-BiMnO3 Checkerboard from First Principles.
Lucia Palova 1 , Premala Chandra 1 , Karin Rabe 1
1 Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey, United States
Show AbstractUsing first principles calculations, we present a magnetostructural effect in an unusual heterostructure, an atomic-scale checkerboard of BiFeO3-BiMnO3. We show that the particular geometry of the checkerboard leads to magnetic frustration and to quasi-degenerate magnetic states; by contrast, these states are energetically well separated in the bulk or layered structures of the constituent materials. We examine the effect of structural distortion on the magnetic ordering. We consider structures generated by most common unstable phonon modes in perovskites, polar zone center and oxygen octahedron rotational boundary modes. We find that the atomic-scale checkerboard has a multiferroic ground state with the desired properties of each constituent material: polar and ferrimagnetic due to BiFeO3 and BiMnO3 respectively. Furthermore, we discuss the possibility of tuning the checkerboard to an energetically close alternative magnetic state by applying an external perturbation that changes the crystal structure, such as strain or an electric field. This structurally-driven magnetic transition allowing switching between nonzero and zero magnetization results in a novel magnetostructural effect in the checkerboard, adding to previous examples of magnetostructural coupling such as bulk and layered manganites, epitaxial EuTiO3 and EuSe/PbSe1−xTex multilayers.
3:30 PM - F2.4
Controlling Exchange Bias Coupling in Ferromagnet-Multiferroic Heterostructures.
Lane Martin 1 , Qing He 2 , John Heron 3 , Ying-Hao Chu 4 , Marta Rossell 5 , Donkoun Lee 6 , Shan Wang 6 , R. Ramesh 2 3 7
1 Mater. Sci. & Eng., Univ. of Illinois, Urbana-Champaign, Urbana, Illinois, United States, 2 Physics, Univ. of California, Berkeley, Berkeley, California, United States, 3 Mater. Sci. & Eng., University of California, Berkeley, Berkeley, California, United States, 4 Mater. Sci. & Eng., National Chiao Tung Univ., HsinChu Taiwan, 5 Nat. Ctr. for Elect. Micro., Lawrence Berkeley Nat. Lab., Berkeley, California, United States, 6 Mater. Sci. & Eng., Stanford Univ., Palo Alto, California, United States, 7 Mater. Sci. Div., Lawrence Berkeley Nat. Lab., Berkeley, California, United States
Show AbstractIncreasing attention has been given to the creation of multiferroic-based heterostructures in an attempt to engineer new functionalities in materials – namely electric field control of ferromagnetism. During this time, a number of groups have studied various manifestations of ferromagnet-multiferroic heterostructures and the exchange coupling that arises. A number of reports have focused on the effect of domain structure of the antiferromagnetic, multiferroic BiFeO3 (BFO) on the properties of ferromagnet-BFO heterostructures. Our group has demonstrated a direct correlation between the underlying ferroelectric domain structure and the exchange coupling observed in Co0.9Fe0.1 (CoFe) / BFO heterostructures. We were able to synthesize BFO films that were predominantly made up of 71° domain walls (referred to as “stripe-like” films due to the stripe-like nature of the domain structure) and films that had a large fraction of 109° domain walls (referred to as “mosaic-like” films due to the complex nature of the domain structure). Detailed studies revealed a direct correlation between the magnitude of exchange bias measured and the total length of 109° domain walls in the BFO film. This served as preliminary evidence to suggest intriguing magnetic structure at domain walls in BFO.Here, we report on the growth and control of crystallographically ordered arrays of 71° and 109° domain walls in BFO. By carefully balancing electrostatic and elastic boundary conditions we can create 1-D nanoscale arrays of these two domain wall types. We will discuss the details of the pulsed laser deposition growth of these films and the evolution of such domain wall arrays through the use of extensive x-ray diffraction, scanning probe microscopy, and transmission electron microscopy studies. We will also present a follow up study of exchange coupled heterostructures based on such domain engineered BFO films to directly probe the role of 71° and 109° domain walls on exchange bias properties. Our findings, which are similar to earlier work, point to a direct correlation between the length of 109° domain walls in a sample and the magnitude of exchange bias that is observed. Finally, we will probe the evolution of magnetic properties of BFO with these different domain structures in an attempt to shed light on reports and questions of enhanced magnetism in BFO. Aided by magnetic measurements using a SQUID magnetometer, the magneto-optic Kerr effect, and synchrotron-based photoemission and dichroism measurements we will report on the connection between domain structure and magnetism in BFO. Preliminary results suggest that BFO films possessing larger fractions of 109° domain walls demonstrate enhanced magnetization. These findings will be presented in conjunction with recent theoretical studies of such domain walls to present a new picture of magnetic properties in the intriguing multiferroic BFO.
3:45 PM - F2.5
Giant Tunnel Electroresistance for Non-destructive Readout of Ferroelectric States.
Manuel Bibes 1 , V. Garcia 1 , A. Crassous 1 , S. Fusil 1 , K. Bouzehouane 1 , S. Enouz-Vedrenne 2 , N. Mathur 3 , A. Barthelemy 1
1 , Unite Mixte de Physique CNRS/Thales and Universite Paris-Sud, Orsay France, 2 , Thales Research and Technology, Palaiseau France, 3 Department of Materials Science, University of Cambridge, Cambridge United Kingdom
Show AbstractFerroelectrics possess a polarization that is spontaneous, stable and electrically switchable, and submicron-thick ferroelectric films are currently used as non-volatile memory elements with destructive capacitive readout. Ultrathin ferroelectric films would enable non-destructive resistive readout by tunnelling, but room-temperature polarization switching at very low thicknesses is challenging. At room temperature, we use piezoresponse force microscopy to show robust ferroelectricity down to 1 nm in highly strained BaTiO3 films, and conductive atomic force microscopy to demonstrate the resistive readout of the polarization state via its influence on the tunnel current. The resulting electroresistance effect scales exponentially with the ferroelectric film thickness, reaching ~75000 % at 3 nm. Our approach exploits the otherwise undesirable leakage current to read the polarization state without destroying it. We demonstrate scalability down to 70 nm, corresponding to potential densities of >25 Gbit/in2. These results pave the way towards ferroelectric memories with simplified architectures, higher densities and faster operation, and should inspire further exploration of the interplay between quantum tunnelling and ferroelectricity at the nanoscale [1]. [1] V. Garcia et al, Nature 460, 81 (2009)
4:15 PM - F2.6
Magnetic Reconstruction at the Interface Between a Hole-Doped Manganite and a Ferroelectric Induced by Polarization Switching.
J. Burton 1 , E. Tsymbal 1
1 Physics and Astronomy, University of Nebraska Lincoln, Lincoln, Nebraska, United States
Show AbstractThe control of magnetization via the application of an electric field, known as magnetoelectric coupling, is among the most fascinating and active materials research areas today. In addition to fundamental scientific interest, magnetoelectric effects may lead to new device applications for data storage and processing. The known mechanisms for magnetoelectric effects include intrinsic effects in single-phase materials, strain induced effects in two-phase composite materials and electronic effects at the surfaces/interfaces of magnetic metals. The exploration of additional mechanisms, however, is still ongoing, stimulated by the search for stronger and more robust magnetoelectric responses.Here we predict [1] a new type of magnetoelectric effect at a ferromagnetic/ferroelectric interface: magnetic reconstruction involving a change in magnetic order at the interface which is induced by electric polarization switching. We consider a hole-doped Lanthanum-manganite, La1-xAxMnO3 (LAMO), where A is a divalent cation that substitutes for trivalent La. This material forms a (001) interface with the prototypical perovskite ferroelectric BaTiO3 (BTO). By choosing the doping level x to be near a transition between magnetic phases we show, using density functional calculations, that the reversal of the ferroelectric polarization of BaTiO3 leads to a change in the magnetic order at the interface from ferromagnetic to antiferromagnetic. This represents a change of the interface magnetic moment of 7 μB per interface Mn atom, and therefore an interfacial magnetoelectric effect that is orders of magnitude larger than those known previously.This new magnetoelectric effect stems from the modulation of the charge density near the interface in the LAMO that is induced to screen the bound polarization charges from the ferroelectric BTO. We demonstrate that this effect is entirely consistent with the magnetic phase transitions in the hole-doped La-manganites occurring with change in their composition. Indeed, the predicted magnetic reconstruction at the interface agrees remarkably well with our calculations of bulk La1-xAxMnO3 compounds with different compositions.This not only opens a new direction in the control of the interface magnetization by electric fields but is also relevant to the recent experiments on magnetoelectric phenomena in manganite/ferroelectric heterostructures.[1] J. D. Burton and E. Y. Tsymbal, arXiv:cond-mat/0904.1726
4:30 PM - **F2.7
Magnetoelectric Correlations in Joint-order-parameter Multiferroics.
Manfred Fiebig 1
1 HISKP, University of Bonn, Bonn Germany
Show AbstractMaterials with a coexistence of magnetic and electric long-range order, called multiferroics, are of great current interest because of their potential to develop pronounced magneto-electric cross-coupling effects. Recently, two fundamentally different types of multiferroics are distinguished: (1) split-order-parameter multiferroics in which magnetic and electric order emerge independently; (2) joint-order-parameter multiferroics in which the magnetic order induces the ferroelectric order. The ferroelectric order in the joint-order-parameter multiferroics is particularly intriguing. Any reversal of the spontaneous polarization is directly coupled to changes in the magnetic order and it is assumed that displacing the electron cloud rather than the ions causes the spontaneous polarization. Here we investigate the relation between magnetic order, electric order, and symmetry for a variety of joint-order-parameter multiferroics by optical second harmonic generation. In spite of the small value of the spontaneous polarization a giant SHG yield is obtained which confirms the electronic origin of the polarization. In MnWO4 we observed domains that behave neither as magnetic nor as electric domains. For example, they display the topology of magnetic domains but they can only be switched by electric fields. Here, designation as "multiferroic" domain seems appropriate. In TbMn2O5 three independent contributions of the Mn and Tb ions to the magnetically induced polarization are uniquely identified and understood on the basis of symmetry arguments. The domain structured of the two Mn-related polarizations are coupled, while Tb-related ferroelectric domains form independently. In summary, spatially resolved investigations of the magneto-electric domain structures in multiferroics prove invaluable for understanding the nature of giant magnetoelectric effects because switching and coupling of magnetic and electric domains forms their basis.
5:00 PM - F2.8
Interfacial Magnetoelectric Coupling in Tricolor Superlattices.
Alex Demkov 1 , Jaekwang Lee 1 , Na Sai 1
1 Physics, The University of Texas, Austin, Texas, United States
Show AbstractWith recent breakthroughs in fabricating high-quality oxide films, ultra thin ferroelectric (FE) films have attracted significant attention. Many FE-based electronic devices proposed to date have a capacitor configuration, where a FE layer is inserted between two identical metal electrodes. We consider theoretically so-called tricolor structures or asymmetric capacitors with one electrode being ferromagnetic and other normal metal. An interesting aspect of a tricolor structure is breaking of the inversion symmetry which is expected to generate new properties. Of particular interest is the control of the magnetization in a ferromagnetic layer without using an external magnetic field. The effect may find applications in low-power and high-density integration in future spintronics devices. To investigate the polarization-dependent magnetization change in the iron layer we construct the tricolor superlattices comprised of Fe/BaTiO3/Pt, Fe/PbTiO3/Pt and perform first principles calculations at the LSDA+U level. We find the electrode magnetization sensitive to the polarization direction in the FE layer, which suggests a multiferroic character of the structure. The effect is much stronger than in the analogous symmetric structures. We also investigate the change of the depolarization field and screening length due to the lattice relaxation This work is supported by the Office of Naval Research under grant N000 14-06-1-0362 and Texas Advanced Computing Center.
5:15 PM - F2.9
Carrier-mediated Magnetoelectric Coupling in Pb(Zr,Ti)O3 / La0.8Sr0.2MnO3 Heterostructures.
Jason Hoffman 1 2 , Carlos Vaz 1 2 , Hajo Molegraaf 3 , Jean-Marc Triscone 3 , Charles Ahn 1 2
1 Applied Physics, Yale University, New Haven, Connecticut, United States, 2 Center for Research on Interface Structures and Phenomena, Yale University, New Haven, Connecticut, United States, 3 DPMC, University of Geneva, Geneva Switzerland
Show AbstractRecent efforts to develop materials with multifunctional capabilities have rekindled interest in multiferroics, which display a coupling between magnetic and electric order parameters. Artificially constructed structures that combine dissimilar magnetic and ferroelectric systems epitaxially have been shown to exhibit enhanced magnetoelectric coupling. While composite multiferroics relying on piezo- or magnetoelastic coupling to modulate magnetic anisotropies have been shown, we demonstrate here a carrier-based coupling between magnetic and electric order parameters in ferroelectric / Sr-doped lanthanum manganite heterostructures. In this work, we employ magneto-optic Kerr effect (MOKE) magnetometry to probe the local magnetic ordering in epitaxial ferroelectric Pb(Zr,Ti)O3 (PZT) / La0.8Sr0.2MnO3 (LSMO) heterostructures, revealing a charge-mediated shift in the magnetic Curie temperature and on/off switching of magnetism. Through M-E (magnetization vs. electric field) measurements we obtain a spin capacitance density η ~ 2 at 100 K.
5:30 PM - F2.10
Magnetoelectric Behavior of PbZr0.53Ti0.47O3/PbFe2/3W1/3O3 Thin Films: A Comparison Between Polycrystalline and Single Crystalline.
Ashok Kumar 1 , Ram Katiyar 1 , Jim Scott 2
1 Physics, University of Puerto Rico, San Juan, Puerto Rico, United States, 2 Physics, Cambridge University, Cambridge United Kingdom
Show AbstractMagnetoelectric multiferroics, which display simultaneous magnetic, electric, and ferroelastic ordering with their coupling, have drawn increasing interest due to their multi-functionality for a variety of device applications such as magnetic field sensors and memory with more than two logic state. Since, only few materials exhibit this kind of behavior at room temperature, intensive research activities are being pursued towards designing solid solution thin films and multilayers of materials with strong magneto-electric (ME) properties at room temperature. One such combination is xPb(Fe2/3W1/3)O3 (PFW) with (1-x)PbZr0.47Ti0.53O3 (PZT) which show good multiferroic properties in polycrystalline and single crystalline thin film forms at room temperature, with polarization loss (<1%), and resistivity (typically 108 ohm.cm) equal to or superior to BiFeO3, and also a new and enormously greater magnetoelectric effect: switching not from +Pr to -Pr with applied H, but from Pr to zero with applied H of less than a Tesla. We switched polycrystalline thin films complete remnant polarization in a sample (with x=.20) from ~ 22 µC/cm2 to zero with merely H=0.5T at 293K, which is more than ~ 1000x greater than the polarization values in rare-earth manganites at cryogenic temperatures. This switching occurs not because of a conventional magnetically induced phase transition, but because of dynamic effects: Increasing H lengthens the relaxation time by x500 from <200 ns to >100 ms, and it couples strongly the polarization relaxation and spin relaxations. The diverging polarization relaxation time accurately fits a modified Vogel-Fulcher Equation in which the freezing temperature Tf is replaced by a freezing field Hf that is 0.91 +/- 0.07 Tesla, with activation energy Ea = 0.26 +/- 0.03 eV and attempt frequency f0 = 40 +/- 1 MHz. The single crystalline thin films showed very high polarization ~ 55 μC/cm2, very high piezo electric response, and well saturated ferromagnetism at room temperatre. Magnetic anisotropy properties were observed across in plane and out of plane magnetization in both of the films. Zero field cool (ZFC) and Field cool (FC) magnetization of single crystalline films indicates significate change in ZFC data around 200 K and a kink at 340 K. Magnetic control of ferroelectric polarization at nano scale for single crystalline thin films will be discussed.
5:45 PM - F2.11
Enhanced Magnetoelectric Coupling in All-thin-film Pb(Zr,Ti)O3/FeGa Multiferroic Magnetic Field Sensors.
Peng Zhao 1 , Zhenli Zhao 2 , Richard Suchoski 1 , Emad Din 1 , Chen Gao 2 , Scott Mathews 3 , Manfred Wuttig 1 , Ichiro Takeuchi 1
1 Dept. of Materials Science and Engineering, University of Maryland, College Park, Maryland, United States, 2 National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, Anhui, China, 3 Dept. of Electrical Engineering and Computer Science, Catholic University of America, District of Columbia, District of Columbia, United States
Show AbstractWe report on enhancement of magnetoelectric (ME) coupling in all-thin-film multiferroic magnetic field sensors. The ME layers consist of a 1-μm thick sol-gel derived Pb(Zr0.52Ti0.48)O3 (PZT) film, a 1-μm thick dc magnetron sputter deposited magnetostrictive Fe70Ga30 (FeGa) film and a 40-nm thick Pt spacer layer. The ac magnetic field sensor devices were fabricated on 35-μm thick Pt pre-coated Si cantilevers, and the laser cutting technique is used to release and isolate the cantilevers. The ME coefficient of a typical cantilever device is 1.8 V/(cm Oe) at the mechanical resonant frequency of the cantilever of 333 Hz and at an optimum bias dc magnetic field of 90 Oe. The Q of the cantilevers in air is ~ 80. We show that the ME coefficient and the device performance can be substantially enhanced by modifying the device geometry and operating the cantilevers in vacuum. By laser cutting simple stress-concentrator legs of mm dimensions at the base of the cantilever, the induced the ME coefficient can by increased by approximately a factor of 3. The Q of the cantilever is boosted to 250 by operating the device in vacuum of 35 mTorr. By implementing these measures, the ME coefficient at the resonant frequency as large as 18 V/(cm Oe) has been achieved in the thin-film devices. The sensitivity of the ac magnetic field detection of the corresponding device is of the order of 10^-9 T at room temperature in vacuum. Progress on fabrication of sensor array devices will also be discussed. This work is supported by NSF MRSEC at UMD (DMR 0520471), ARO W911NF-07-1-0410, and ONR N000140610530.
F3: Poster Session: Processing and Characterization
Session Chairs
Tuesday AM, December 01, 2009
Exhibit Hall D (Hynes)
9:00 PM - F3.1
Development of PLZT Film-on-Foil Capacitors with High Dielectric Strength.
Beihai Ma 1 , Manoj Narayanan 1 , U. (Balu) Balachandran 1
1 Energy Systems Division, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractFerroelectric film-on-foil capacitors hold special promise to replace discrete passive components in the development of electronic devices that require greater performance and smaller size. We have deposited ferroelectric Pb0.92La0.08Zr0.52Ti0.48O3 (PLZT) films on base metal (nickel and copper) substrates by chemical solution deposition. Measurements at room temperature on PLZT film-on-foil capacitors with Pt top electrodes have indicated excellent performance: relative permittivity of ≈1300, dielectric loss (tan δ) of ≈0.05, leakage current density of ≈6×10-9 A/cm2, and dielectric strength of >6 MV/cm. A series of highly accelerated lifetime tests was performed to determine the reliability of these ferroelectric film-on-foil capacitors under high temperature and high field stress. Samples were exposed to temperatures ranging from 100 to 150°C and electric fields ranging from 8.7x105 V/cm to 1.3x106 V/cm. The breakdown behavior of the samples was evaluated by Weibull analysis. The activation energy was determined to be ≈0.35 eV when an electric field of 1.05x106 V/cm was applied. The voltage acceleration factor was ≈-6.3 at 100°C. The mean time to failure was projected to be >3000 hr at 100°C with a dc electric field of ≈2.6x105 V/cm. Details of processing conditions, dielectric properties, and reliability analysis will be presented.Work was supported by the U.S. Department of Energy, Office of Vehicle Technologies Program, under Contract DE-AC02-06CH11357.
9:00 PM - F3.10
Combinatorial Materials Libraries of BaF2/SrF2/CaF2 Doped Bi-V-O Thin Films by 90° Off-axis Reactive Sputter.
Hanjong Paik 1 , Taro Naoi 1 , R. Bruce van Dover 1
1 Materials Science and Engineering, Cornell University, Ithaca, New York, United States
Show AbstractWe report the effect of alkaline-earth fluoride doping on the electrical and structural properties of Bi-V-O thin films using continuous compositional spreads synthesis and analysis technique. 90° off-axis reactive sputter was utilized to fabricate and characterize samples with over than 1000 different compositions in libraries of BaF2/SrF2/CaF2 doped Bi-V-O system. X-ray diffraction (XRD), micro-Raman studies revealed the structural variation according to the alkaline-earth fluoride doping on the layered Aurivillious-related Bi-V-O compounds. Electron probe micro-analyzer (EPMA), x-ray photoelectron microscopy (XPS) is used to the compositional variation, and the effects of valence change of anion ions on the electrical properties are considered. Electrical characterization of the dielectric constant, remnant polarization, and leakage current characteristics were mapped onto a pseudo-ternary phase diagram. This novel compositional spread approach will open the chance for new ferroelectric phase investigation.
9:00 PM - F3.11
Multiferroic Bi(Fe1-xNdx)O3, (Bi1-x Fex)FeO3, and Bi (Fe0.95Li0.05) O3 Thin Films by Chemical Solution Deposition.
Ricardo Melgarejo 1 , Reji Thomas 1 , Ram Katiyar 1
1 Department of Physics and Institute for Functional Nanomaterials, University of Puerto Rico, San Juan, Puerto Rico, United States
Show AbstractThe multiferroic (MF) materials exhibit ferroelectric/ferrielectric/antiferroelectric properties in combination with ferromagnetic/ferrimagnetic/antiferromagnetic and/or ferroelastic properties. Possible applications of these kinds of materials include multiple-state memory elements, electric field controlled ferromagnetic resonance devices and variable transducers with either magnetically-modulated piezoelectricity or electrically-modulated piezomagnetism and hence the recent interest is driven by the long-term technological aspirations. BiFeO3 (BFO) belongs to this materials class and has been widely investigated in the past years. It has a rhombohedrally distorted perovskite structure with the space group R3c, exhibiting multiferroism at room temperature with antiferromeagnetic ordering below the Neel temperature (Tn ~ 643 K) and ferroelectric ordering below the Curie temperature (Tc~ 1103K). Magnetic and ferroelectric property in BFO is due to the canting of the Fe3+ spin structure and stereo chemically active 6s2 lone pair of Bi3+, respectively. However, weak magnetic property and relatively high leakage current density obstruct its practical applications. To improve the magnetic properties without disturbing the ferroelectric properties and to obtain a well-saturated ferroelectric hysteresis loop by reducing the leakage current without destroying the magnetic properties are essential for its real use in device applications involving mutual control of magnetization and polarizationBiFe1-xNdxO3 (x = 0.00, 0.01, 0.05, 0.07, 0.10) and BiFe0.95Li0.05O3 thin films were prepared by chemical solution deposition on Pt/Ti/SiO2/Si substrates. X-ray diffraction and Raman scattering studies revealed distorted rhombohedral R3c structure for pure and substituted BiFe1-xMxO3 (x≤5%) films. The solubility limit of Nd substitution in BiFeO3 is close to 5% as higher concentrations (>5%) resulted in the formation of Bi25FeO40 phase. The surface roughness increased with the Li and Nd substitution and is due to the enhanced grain growth. The dielectric constant of the substituted BFO films increased gradually with the increased Nd and Li content. The leakage current density of the Nd and Li substituted BFO films were about two orders of magnitude lower than of BFO. Presumably due to lower leakage current compared to BFO and BiFe1-xNdxO3 (x≥5%) films, BiFe0.99Nd0.01O3 and BiFe0.95Li0.05O3 films showed better P-E hysteresis. The saturation magnetization of BiFe0.95Li0.05O3 increased from 3.2emu/cm3 to 8.5 emu/cm3 with remanent magnetization ~ 0.5 emu/cm3 and coercive field ~ 0.10 kG. Apart from this interesting results based on Fe excess in the system (Bi1-xFex) FeO3 also will be discussed.
9:00 PM - F3.12
Grown and Characterization of Single Phase Multiferroics Pb{(Zr0.53Ti0.47)1-x(Fe1/2Ta1/2)x}O3 Thin Films by Pulsed Laser Deposition.
Dilsom Sanchez 1 , Ashok Kumar 1 , Ram Katiyar 1
1 Physics, University of Puerto Rico, Rio Piedras campus, San Juan , Puerto Rico, United States
Show AbstractHighly oriented Pb{(Zr0.53Ti10.47)1-x(Fe1/2Ta1/2)x}O3 (x = 0.1, 0.2, 0.3, 0.4) thin films were fabricated on MgO substrates by pulsed laser deposition technique, these films were annealed in-situ at 6000C for 50 minutes on oxygen atmosphere to get the desired phase and single crystallinity. The x-ray diffraction (XRD) diffraction analysis indicated that the pyrochlore phase was transformed to the perovskite phase after annealing. These materials showed very good ferroelectric polarization at room temperature ~50 to 20 µC/cm2, although these properties decrease with the increase of Fe and Ta compositions. The ferromagnetic properties were observed in all composition at room temperature; however the high concentration of Fe and Ta leads to better magnetic saturation (~6-36 µemu). These films illustrated high dielectric constant, low dielectric loss, high resistivity, and low leakage current at room temperature whereas these properties detoriate with the increase of Fe and Ta concentration. Among all the composition x~ 0.20 % showed very potential candidate for room temperature multiferroics. The maxima dielectric constant lies in between 300 to 530 K which shifted to lower temperature side with increase in Ta and Fe concentration. Room temperature magnetization vs applied magnetic field showed well behaved well saturated magnetic hysteresis above x ≥ 0.20. Especially, x =0.20 indicates magnetic anisotropy at room temperature. These results show that the prepared materials have excellent multiferroic properties at room temperature.
9:00 PM - F3.13
Growth and Dielectric Characterization of Low Molecular Weight Organic Ferroelectric Thin Films.
Nicholas Thompson 1 , Adam Jandl 2 , Josef Spalenka 2 , Paul Evans 1 2
1 Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States, 2 Materials Science Center, University of Wisconsin-Madison, Madison, Wisconsin, United States
Show AbstractA recently synthesized class of organic supramolecular single crystals exhibit displacive ferroelectricity [1]. Among other properties similar to inorganic ferroelectric materials, these hydrogen-bonded cocrystal compounds display a sharp divergence in their dielectric constant near the Curie temperature. We have created thin films of the prototypical compound in this class, phenazine-chloranilic acid. The films were produced by simultaneously evaporating phenazine and chloranilic acid from solid sources onto a substrate held at 130 K. Under these conditions, the films were porous and consisted of interconnected small crystals. Evaporation onto a room temperature substrate did not produce a film. Powder x-ray diffraction shows that these films possess the planar spacings previously reported for bulk phenazine-chloranilic acid crystals. Despite the porosity, the effective dielectric constant of the films was 10 at 293 K and increased to 14 at 125 K. The effective resistivity of the film is 10 TΩ cm, based on steady-state current-voltage measurements. These dielectric and leakage properties are already comparable to ferroelectric polymers and improvements are expected with a reduction in the porosity. [1] S. Horiuchi, F. Ishii, R. Kumai, Y. Okimoto, H. Tachibana, N. Nagaosa, and Y. Tokura, Nature Mat. 4, 163 (2005).
9:00 PM - F3.14
One-axis Oriented 4Ti4O15 and SrBi4Ti4O15 Films Prepared on Silicon Wafer by Chemical Solution Deposition Technique.
Hiroshi Uchida 1 , Yuki Mizutani 1 , Hiroshi Funakubo 2 , Seiichiro Koda 1
1 Department of Materials and Life Sciences, Sophia University, Tokyo Japan, 2 Department of Innovative and Engineered Materials, Tokyo Institute of Technology, Yokohama Japan
Show AbstractOne-axis oriented bismuth layer-structured ferroelectric (BLSF) films were designed using perovskite buffer layers for assembling the crystal orientation and the ferroelectric / dielectric properties of the BLSF crystals on silicon wafer. BLSF crystals have anisotropic crystal structure which consists of bismuth oxide layers and pseudo-perovskite blocks with the general formula of (Bi2O2)2+-(Am-1BmO3m+1)2-, where A is mono-, di-, or trivalent ions, B is tetra-, penta-, or hexavalent ions, and m is the number of BO6 octahedra in pseudo-perovskite blocks. Earlier researches revealed that the BLSF crystals possess excellent dielectric permittivity with lower size effect and temperature coefficient of capacitance (TCC), as well as high electrical resistivity along to the c-axis direction.[1] These phenomena would contribute for constructing high performance ferroelectric / dielectric devices driven under harsh environment, e.g., at high-temperature condition above 100oC. In this research, thin films of CaBi4Ti4O15 and SrBi4Ti4O15, kinds of BLSF compounds with m = 4, were prepared by chemical solution deposition (CSD) technique on (100)LaNiO3/(111)Pt/(100)Si and (100)SrRuO3//(100)LaNiO3/(111)Pt/(100)Si substrates. These films consisted of crystalline phase of BLSF crystal with preferential crystal orientation of (00l) plane normal to the substrate surface. Anisotropic crystal growth of BLSF occurred by the lattice matching between pseudo-perovskite blocks in BLSF crystal and (100)SrRuO3 and (100)LaNiO3 plane with perovskite structure. The leakage current density of one-axis oriented CaBi4Ti4O15 and SrBi4Ti4O15 films were in the range below 10-6 A/cm2 under applied electric field up to approximately 100 kV/cm2. The dielectric constants (εr) of one-axis oriented CaBi4Ti4O15 and SrBi4Ti4O15 thin films were approximately 250 at room temperature, which is significantly higher than those of other BLSF films with m = 2 - 3. The εr values of both films increased slightly with ambient temperature. The variations of capacitance at a temperature range from 25 to 200oC were approximately 3 and 5 % respectively, which were significantly smaller than (Ba,Sr)TiO3 thin film and would satisfy the performance requirement for driving at high-temperature condition. [1] K. Takahashi, et al., Appl. Phys. Lett. 89 (2006) 082901., and many other articles.
9:00 PM - F3.15
Effect of the Low Oxygen Pressure on Phase Evolution in Epitaxial BaTiO3-CoFe2O4 Thin Films.
Kyoung Sun Kim 1 , Seung Ho Han 1 , Young Taek Lee 2 , Ho Gi Kim 1 , Jeong Seog Kim 3 , Chae Il Cheon 2
1 Materials Science and Engineering, KAIST, Daejeon Korea (the Republic of), 2 Materials Science and Engineering, Hoseo University, Asan, Chungnam, Korea (the Republic of), 3 Semiconductor and Display Engineering, Hoseo University, Asan, Chungnam, Korea (the Republic of)
Show AbstractMany researchers have interested in magentoelectric multiferroics recently. Even though magnetoelectric coupling was found in single multiferroic materials, it was too small or appeared at very low temperature. The ferroelectric-ferromagnetic composite materials are one of the candidates for strong magnetoelectric materials. These composite materials show strong magnetoelectric coupling through stain effect. Among the ferroelectric-ferromagnetic composite materials, the spinel-perovskite composite films have self-assembled nanostructure over specific deposition conditions. This phenomenon severely depends on growth rates. However phase separation effect at low oxygen pressure has rarely reported yet. In this study we will investigate the phase separation of 0.6BaTiO3-0.4CoFe2O4 (0.6BT-0.4CF) nanocomposite films prepared at low oxygen pressure. The epitaxial 0.6BT-0.4CF nanocomposite films were prepared on STO (100) substrate by pulsed laser deposition at various temperature and working pressure. Many researchers had reported that the phase separation of this composition generally took place over 750°C at 100mTorr. And the phase separation was retarded with decreasing oxygen working pressure because the films had higher growth rates. At specific oxygen working pressure, the phase separation did not occur. However, although the 0.6BT-0.4CF films prepared by low oxygen working pressure had highest growth rate, the phase separation occurred. This behavior was clearly different from the samples prepared at high oxygen pressure. This phenomenon also took place lower deposition temperature than upper mentioned that. And the square shaped morphology with several tens nanometers appeared on the surface. The structural, magnetic, electric and coupling properties of 0.6BT-0.4CF nanocomposite films deposited at low oxygen pressure will be discussed.
9:00 PM - F3.16
BST Films Grown By Metal Organic Chemical Vapor Deposition Incorporating Real-Time Control Of Stoichiometry.
David Boyd 1
1 Division of Engineering and Applied Science, California Institute of Technology, Pasadena, California, United States
Show AbstractThis presentation will focus on the growth of BaSrTiO3 (BST) films by metal organic chemical vapor deposition (MOCVD). For advanced heterostructures such as compositionally graded films, careful control of the stoichiometry is required. The basis for controlling film stoichiometry is controlling the rate at which precursor molecules reach the heated substrate, and for BST films, this involves control of three separate vaporized precursors. The vapor phase is achieved by sublimation of the precursors which in turn is directly dependent on their temperature. With any real system, this temperature may drift and the precursors may even degrade during the time of growth. This can affect both the growth rate and the stoichiometry of the film. To overcome these issues, we have incorporated UV spectroscopy to monitor and control in real-time the molar flux of the precursors. Optical control of the molar flux hinges on the knowledge of the molar absorbtivities of the precursor molecules. In this presentation, I will present measurements of the molar absorbtivities of BST metalorganic precursors as well as the MOCVD growth and characterization of BST thin films.
9:00 PM - F3.17
PZT Piezoelectric Films on Glass for Gen-X Imaging Systems.
Rudeger Wilke 1 , Susan Trolier-McKinstry 1 , Paul Reid 2
1 Materials Research Institute, Pennsylvania State University, University Park, Pennsylvania, United States, 2 Smithsonian Center for Astrophysics, Harvard University, Cambridge, Massachusetts, United States
Show AbstractThe use of piezoelectric lead zirconate titanate (PZT) for actuation of elements in space based mirrors for X-ray telescopes requires the development of processing technology to deposit high quality PZT thin films on glass substrates. We present synthesis and optimization of sol-gel deposited 0.9 μm thick films of PbZr0.52Ti0.48O3 on Pt/Ti/glass substrates. In order to avoid warping of the glass at temperatures typically used to crystallize PZT films (~700 °C) a lower temperature two step crystallization process was employed. An initial ~80 nm thick seed layer of PbZr0.30Ti0.70O3 was deposited to promote the growth of the perovskite phase. After the deposition of the seed layer, the films were annealed in a rapid thermal annealing (RTA) furnace at 550 °C for 3 minutes to nucleate the perovskite phase. This was followed by isothermal annealing at 550 °C for 1 hour to promote full crystallization. For the subsequent PbZr0.52Ti0.48O3 layers, the same RTA protocol was performed, with the isothermal crystallization implemented following the deposition of three PbZr0.52Ti0.48O3 spin-coated layers. Over the frequency range of 1 kHz to 100 kHz, films exhibit relative permittivity values near 800 with loss tangents below 0.07. Hysteresis loops show low levels of imprint with coercive fields of 40-50 kV/cm in the forward direction and 50-70 kV/cm in the reverse direction. Remnant polarization varied from 25-35 μC/cm2 and e31 values were approximately -5.0 C/m2. The use of these films for adaptive figuring of the X-ray telescope optics will be discussed.
9:00 PM - F3.18
Ag(TaxNb1-x)O3 Thin Films on SrRuO3/LaAlO3(001)p Substrates.
Raegan Johnson-Wilke 1 , D. Tinberg 1 , S. Trolier-McKinstry 1 , Y. Han 2 , I. Reaney 2 , M. Telli 3 , I. Levin 4 , D. Fong 5 , T. Fister 5 , S. Streiffer 5
1 Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania, United States, 2 Department of Engineering Materials, University of Sheffield, Sheffield United Kingdom, 3 Department of Metallurgical Engineering, Celal Bayar University, Manisa Turkey, 4 Materials Science and Engineering Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 5 Materials Science Division, Argonne National Lab, Argonne, Illinois, United States
Show AbstractTheoretical calculations using AgNbO3 as an end member for PbTiO3, BaZrO3, and BaTiO3 have shown that these solid solutions possess a morphotropic phase boundary with favorable piezoelectric properties [1], making the Ag(TaxNb1-x)O3 a potential end member candidate for lead-free piezoelectrics. It is therefore essential that the structural and electrical properties of Ag(TaxNb1-x)O3 thin films be understood. Bulk Ag(TaxNb1-x)O3 is known to have a complex phase transition sequence which includes several phases with tilted oxygen octahedra. In perovskite structures, when the A-site atom is too small for the interstice, the oxygen octahedra will tilt to decrease the volume of the A-site, resulting in improved structural stability of the cell. It is anticipated that the in-plane strains in epitaxial thin films may influence the relative stability of the tilted phases. Understanding the relationship between strain and octahedral tilting allows for the potential to engineer film properties. We report on the phase transition sequence of Ag(TaxNb1-x)O3 thin films on SrRuO3/LaAlO3(001)p, LaAlO3(001)p and SrTiO3(001)p substrates. Ag(TaxNb1-x)O3 films were grown by chemical solution deposition. The solution was spun on crystalline substrates and subjected to two pyrolysis steps at 200 °C and 450 °C before crystallization at 750 °C. Film thicknesses ranged from 20-300 nm. At room temperature, relaxed Ag(Ta0.5Nb0.5)O3 films adopt a different structure than the bulk material. Using Glazer notation, the tilt system at room temperature was found to be a-a-a- with rhombohedral symmetry. This phase was observed at increasing temperatures until the material transformed to cubic. This is significantly different than bulk ceramics and single crystals of the same composition, which have an orthorhombic symmetry with a-b-c-/a-b-c+ tilt system at room temperature. As the bulk material is heated, it transitions through another orthorhombic phase, followed by a tetragonal phase and finally into the cubic phase. Electron diffraction of the Ag(Ta0.5Nb0.5)O3 films shows the emergence of quadrupling of the unit cell (which is due to the a-b-c-/a-b-c+ tilt system) at low temperature, namely, around 60 K. Low temperature electrical measurements confirm the existence of a phase transition near 60 K with a peak permittivity near 225. The end member AgNbO3 films have a much higher room temperature permittivity than bulk, 400 and 120 respectively. Temperature dependent electrical data indicates a different phase transition sequence compared to bulk. This work, in addition to structural data on relaxed films of different compositions, will be presented.[1] I. Grinberg, A. Rappe, “Silver Solid Solution Piezoelectrics,” Applied Physics Letters, 85, 10, 1760, (2004)
9:00 PM - F3.19
Growth, Characterization and Magnetoelectric Properties of Epitaxial NiFe2O4/BiFeO3 Heterostructures.
Jose Pardo 1 2 3 , P. Yu 1 , C. Magen 4 5 , M. Gajek 1 , Steven Crane 6 7 , Eric Dhall 1 , Lane Martin 1 8 9 , M. Ibarra 3 5 , R. Ramesh 1 7 8
1 Dept. of Physics, University of California at Berkeley, Berkeley, California, United States, 2 Dpto. de Ciencia y Tecnologia de Materiales y Fluidos, & Instituto de Nanociencia de Aragon, University of Zaragoza, Zaragoza Spain, 3 Instituto de Nanciencia de Aragon, Universidad de Zaragoza, Zaragoza Spain, 4 Instituto de Nanociencia de Aragon-ARAID, Universidad de Zaragoza, Zaragoza Spain, 5 Dpto. de Fisica de la Materia Condensada, Universidad de Zaragoza, Zaragoza Spain, 6 , Exponent, Inc., Menlo Park, California, United States, 7 Dept. of Materials Science and Engineering, University of California at Berkeley, Berkeley, California, United States, 8 Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 9 Dept. of Materials Science and Engineering, University of Illinois, Urbana-Champaign, Illinois, United States
Show AbstractElectric field control of ferromagnetism is currently a field of great scientific and technological interest. Although a room temperature ferromagnetic-ferroelectric multiferroic has yet to be achieved, current research is focused on artificially engineered composites and heterostructures that give rise to similar functionality through exchange coupling interactions. Initial studies have shown that heterostructures of all oxide ferromagnetic-multiferroic materials exhibit strong coupling only at low temperatures. Thus it appears that the Curie temperature of the ferromagnet is a critical value in determining the possibility of room temperature coupling and functionality. We are therefore exploring heterostructures of spinels (such as NiFe2O4 and CoFe2O4) as candidate oxide ferrimagnets that can be grown epitaxially on a multiferroic such as BiFeO3.Pulsed laser deposition was used to grow epitaxial NiFe2O4 films with different thickness between 1 and 25 nm on top of 50 nm-thick epitaxial BiFeO3 layers. X-ray diffraction and transmission electron microscopy were used to characterize the heterostructures, interfaces and epitaxial strain. Initial studies reveal the presence of strong exchange coupling in these heterostructures. We will discuss in detail the evolution of such coupling as a function of temperature, spinel film thickness, substrate, and deposition conditions.
9:00 PM - F3.2
Room Temperature Ferromagnetism and Silicon Integration of Sr(Ti1-xCox)O3 Epitaxial Films.
Lei Bi 1 , Hyun-Suk Kim 1 , Gerald Dionne 1 2 , Caroline Ross 1
1 DMSE, MIT, Cambridge, Massachusetts, United States, 2 , Lincoln Laboratory, Lexington, Massachusetts, United States
Show AbstractMultiferroic materials with both intrinsic ferromagnetic and ferroelectric properties have attracted great research interest in recent years due to their potential application in a variety of advanced devices. However, coexistence of room temperature ferromagnetic and ferroelectric properties has rarely been observed in materials, because ferromagnetic insulators with high Curie temperature are usually structurally centro-symmetric. Therefore, it is important to explore new materials with room temperature ferromagnetism for multiferroic applications.One possible way to achieve intrinsic multiferroicity is to introduce non-d0 transition metal ions into the crystal lattice of ferroelectric materials, such as perovskite structured titanates (BaTiO3, Ba1-xSrxTiO3, PbTiO3 etc.). In this study, we report structure, magnetic properties and silicon integration of epitaxial Sr(Ti1-xCox)O3 (x=0.05, 0.1, 0.2, 0.3 and 0.5) films grown by pulsed laser deposition. When epitaxially grown on LaAlO3(001) substrates, the crystal symmetry of the Sr(Ti0.7Co0.3)O3 film is rendered tetragonal under in-plane biaxial stress as confirmed by X-ray reciprocal space map (RSM), which is considered to be beneficial to ferroelectric properties in perovskite structured titanates. Sr(Ti0.8Co0.2)O3 and Sr(Ti0.7Co0.3)O3 films were observed to be highly insulating and room temperature ferromagnetic with saturation magnetizations of 0.23μB/Co and 0.42μB/Co respectively. The formation of magnetic secondary phases such as Co metal clusters in Sr(Ti0.7Co0.3)O3 is excluded based on X-ray diffraction (XRD), cross sectional TEM, X-ray photoelectron spectroscopy (XPS) and X-ray-absorption near edge spectral analysis (XANES). A large magneto anisotropy is observed in Sr(Ti0.7Co0.3)O3 films, which is attributed to magnetoelastic effects. Silicon integration of the Sr(Ti0.7Co0.3)O3 was also studied. By using CeO2/YSZ (Yttrium stabilized ZrO2) double buffer layers, epitaxial Sr(Ti0.7Co0.3)O3 films were successfully grown on Si(001) substrates as confirmed by 1DXRD and 2DXRD measurements. The ferromagnetism origin of Sr(Ti0.7Co0.3)O3 will be analyzed based on its magnetoelastic effects. The ferroelectric properties of these films will also be discussed.
9:00 PM - F3.22
Fabrication and Ferroelectric/Ferromagnetic Characterization of LuFe22O4 Thin Films Deposited by Dual Laser Ablation.
Sarath Witanachchi 1 , Jason Rejman 1 , Tara Dhakal 1 , Pritish Mukherjee 1
1 Physics, University of South Florida, Tampa, Florida, United States
Show AbstractLuFe2O4 falls in the category of charge frustrated material systems and exhibit interesting ferroelectric, magnetodielectric and spin-charge ordering effects. Even though, the fundamental properties of the bulk material have been investigated, no work on thin films has been reported to date. In this paper we report the growth of LuFe2O4 thin films by using a dual-laser ablation process. Formation of the LuFe2O4 phase is dependent on the fluence of the laser used for ablation. Single excimer laser deposited films for laser fluencies below 2 J/cm2 were amorphous and required a post annealing step to form the crystalline phase. However, films deposited by dual laser ablation, where ablation is caused by spatially overlapped and temporally synchronized excimer and a CO2 pulsed lasers, showed crystallinity without any post treatment. The ferroelectric polarization vs. voltage data for these films yielded values of 0.61 μC/cm2 at room temperature and 3.292 μC/cm2 at 200 K. Thin films produced a magnetization of 150 emu/cm3 at room temperature and 200 emu/cm3 at 10 K. Dependence of the ferroelectric and ferromagnetic properties on growth conditions will be presented.
9:00 PM - F3.23
Effects of LSCO Buffer Layer on the Microstructure and Dielectric Properties of Ba0.6Sr0.4TiO3 Films Prepared by Sol-gel Methods.
Songwei Han 1 , Jinrong Cheng 1 , Shengwen Yu 1
1 , Shanghai University, Shanghai China
Show AbstractIn this work, Ba0.6Sr0.4TiO3(BST) thin films were deposited on Ti substrates using conductive La0.5Sr0.5CoO3 (LCSO) as buffer layers. Both BST and LSCO films were prepared by sol-gel methods. The structure and morphology of BST and LSCO films were analyzed by X-ray diffraction (XRD) and scanning electron microscope (SEM). XRD results show that both BST and LSCO films have perovskite structure with random orientation. The dielectric properties of BST films were dependent on the thickness of LSCO buffer layers. Upon using LSCO buffer layers, the dielectric properties of BST films were significantly improved. The dielectric constant, tunability, and dielectric loss of BST thin films for LSCO of 150 nm achieved about 511, 0.03 and 36.7% respectively.
9:00 PM - F3.25
Chemical Solution Deposited High Tc xBiInO3-(1-x)PbTiO3 Piezoelectric Films.
Song Won Ko 1 , Hong Goo Yeo 1 , Susan Trolier-McKinstry 1
1 Materials Research Institute, Pennsylvania State University, State College, Pennsylvania, United States
Show AbstractNew piezoelectric thin films with high Curie temperatures (Tc) are desirable for low voltage actuators in harsh conditions. The properties of chemical solution deposited xBiInO3-(1-x)PbTiO3 (BI-PT) thin films on platinized silicon substrates were investigated because it was predicted that BI-PT should have a Tc > 500oC. Using a PbTiO3 seed layer, phase pure xBiInO3-(1-x)PbTiO3 (0.10≤x≤0.35) thin films were prepared. For a 470 nm thick 0.15BiInO3-0.85PbTiO3 film, the room temperature permittivity was 650, while the dielectric loss tangent was below 2%. The coercive field and remnant polarization were 73 kV/cm and 21.6 μC/cm2 respectively. The ferroelectric transition temperatures of the xBiInO3-(1-x)PbTiO3 (x=0.10 - 0.20) films were all in excess of 550 °C. For x = 0.15, the e31,f piezoelectric coefficient was -2.7 C/m2.
9:00 PM - F3.26
Structural, Magnetic, and Electrical Properties of BiMnxFe1-xO3 Thin Films.
Danilo Barrionuevo 1 , Surinder Singh 2 , Maharaj Tomar 3
1 Physics, University of Puerto Rico Mayaguez, Mayaguez, Puerto Rico, United States, 2 Engineering Science and Materials, University of Puerto Rico Mayaguez, Mayaguez, Puerto Rico, United States, 3 Physics, University of Puerto Rico Mayaguez, Mayaguez, Puerto Rico, United States
Show AbstractMultiferroic materials have attracted research interests for novel bifunctional devices. Bismuth ferrite (BiFeO3) related materials have shown ferromagnetic and ferroelectric properties. Room temperature ferroelectricity has been observed in many electroceramics. However, room temperature ferromagnetism is required for practical bifunctional devices. In the present study, we have synthesized BiMnxFe1-xO3 (x = 0.00, 0.025, 0.035, 0.04, 0.07, 0.1, 0.15, 0.2, 0.25, 0.30) by sol gel process and thin films were deposited by spin coating on Pt/SiO2/Si substrate. X-ray diffraction shows rhombohedrally distorted BiFeO3 structure, and Mn ion substitutes Fe site in the structure for low concentration. Magnetic saturation has been observed at room temperature with increased Mn substitution. On the other hand, leakage current measurements suggest that the resistivity of the films decreases with increasing Mn ion concentration. Raman studies suggest the dopant induced structural distortion.
9:00 PM - F3.27
Chemical Design of Multilayered Hybrid Ferroelectric-Ferromagnetic Nanostructures by Liquid Phase Deposition.
Gabriel Caruntu 1 2 , Shiva Prassad Adireddy 1 2 , Cuikun Lin 1 2 , Amin Yourdkhani 1 2
1 Chemistry, University of New Orleans, New Orleans, Louisiana, United States, 2 , Advanced Materials Research Institute, New Orleans, Louisiana, United States
Show AbstractMagnetoelectric heterostructures obtained by coupling piezoelectric and magnetostrictive layers have become extremely attractive, from both theoretical and practical viewpoint because they can mimic the functionality of “true” single-phase multiferroic materials. Owing to their assembled nature, many degrees of freedom which are not accessible in single-phase multiferroic materials are available for tailoring the response in these hybrid materials. Therefore a special focus has been put on the fabrication of nanoscale hybrid magnetoelectric composites. However, to date most of these structures are obtained either by physical methods such as the mechanical assembly of a magnetostrictive material with a ferroelectric phase or by lamination, sputtering or pulse laser deposition. We have used a simple, highly versatile chemical approach for the design of multilayered 2-D heterostructures consisting of alternate layers of ferroelectric and ferromagnetic materials. In this method, well adherent spinel-type transition metal ferrite films MFe2O4 (M=Co, Ni) were deposited on technologically relevant substrates by the hydrolysis of metal fluoride complexes at low temperatures (<90 oC) in the presence of a F- ions scavenger, such as boric acid. The resulting ferrite films were subsequently used as substrates for the deposition of a second perovskite-type ABO3 (BaTiO3, PbZrxTi1-xO3, etc.) layer by the same soft solution-based approach. By repeating this procedure ferroelectric/ferromagnetic multilayered hybrid structures with a tunable number and thickness of the constituent layers can be constructed. Because the hydrolysis yields usually generate stoichiometric mixtures of hydroxides/oxyhydroxides, a heat treatment at 600 oC in air is needed for the stabilization of the desired crystalline structures. By changing the chemical identity of the metals we were able to vary the chemical composition of the films in a wide range. The intimate mixing of the precursors at the molecular level along with the low processing temperature allows for the creation of direct junctions between the magnetostrictive phase and a ferroelectric material with fairly large relative interfacial areas. The influence of several parameters, such as the temperature, concentration of the cations/scavenger in the treatment solution and the time of deposition of the morphology of the nanoparticulate films was studied in detail. The magnetic properties of the hybrid multilayered structures have revealed that the coercivity of the magnetic phase is influenced by the number of the layers in the structure. For example, the coercivity of a single CoFe2O4 layer measured at room temperature is 1.86 kOe and increases by 28.5% (Hc=2.39 kOe) upon addition of a second BaTiO3 layer with a comparable thickness (250 nm) and decreases by 14.8% (Hc=2.05 kOe) when a third CoFe2O4 layer is added indicating the existence of a magneto-electric coupling between the spinel-type and perovskite layers.
9:00 PM - F3.28
Preparation of Ferroelectric Nanoisland Array Using Blockcopolymer Self-Assembly.
Youngsuk Kim 1 , Hee Han 2 3 , Younseok Kim 3 , Sunggi Baik 2 , Jin Kon Kim 1
1 Dept.of Chem.Eng., POSTECH, Pohang, Kyungbuk Korea (the Republic of), 2 Dept. of Mater. Sci.&Eng., POSTECH, Pohang, Kyungbuk Korea (the Republic of), 3 , Max-Planck Institute for Microstructure Physics, Halle Germany
Show AbstractPbTiO3 (PTO) nanoisland array was fabricated by a simple method based on block copolymer micelles. PTO precursor was encapsulated within poly(4-vinylpyridine) block of polystyeren-b-poly(4-vinylpyridine) copolymer micelles. The micelle solution was spin-coated on a single crystalline Nb-doped SrTiO3 to form monolayer of micelles. Block copolymer thin film was removed and PTO islands were epitaxially crystallized under atmospheric environment at 600°C. Epitaxial relationship between the substrate and PTO islands was analyzed by X-ray diffraction (XRD) and ferroelectric behavior was observed by piezoresponse force microscopy (PFM). The average diameter and height of each PTO nanoisland are ~30 nm and 6nm, respectively. Each nanoisland exhibited a distinct ferroelectric property with the polarization axis aligned normal to the substrate.AcknowledgementThis work was supported by the National Creative Research Initiative Program supported by Korea Organization of Science and Engineering Foundation (KOSEF). X-ray diffraction (3C2 and 10C1) was performed at PLS beamlines supported by POSCO and KOSEF.
9:00 PM - F3.29
Effect of Zr-doping on the Structure and Properties of Chemical Solution Deposited BiFeO3 Thin Films.
Somdutta Mukherjee 1 , Rajeev Gupta 1 2 , Ashish Garg 3
1 Department of Physics, Indian Institute of Technology Kanpur, Kanpur, U. P, India, 2 Materials Science Programme, Indian Institute of Technology Kanpur, Kanpur, U. P, India, 3 Materials and Metallurgical Engineering, Indian Institute of Technology Kanpur, Kanpur, U.P., India
Show AbstractIn this work we report the structural and electrical characterization studies of BiFeO3 thin films doped with Zr4+, an aliovalent ion, on Fe3+ site. BiFe(1-x)ZrxO3 (BFZO) films (x = 0.0 to 0.15) were deposited by chemical solution deposition on platinized Si substrates followed by post annealing in nitrogen at 650oC. X-ray diffraction patterns show pure phase of BiFeO3 is obtained on doping up to 15 at. % Zr doping followed by appearance of secondary phases suggesting the limit of doping ~15 at. %. Raman measurements were done to understand the structural modification due to Zr4+ substitution. Refinement of the XRD data suggests that the films posses a monoclinic structure than equilibrium rhombohedral structure. This was further substantiated by the increased number of modes in Raman spectra of the samples. Polarization and room temperature impedance measurements were carried out to study the effect of Zr4+ doping on ferroelectric behaviour, dielectric loss and leakage in these films.
9:00 PM - F3.3
Dielectric and Piezoelectric Properties in Mn-modified (1-x)BiFeO3-xBaTiO3 Ceramics.
Serhiy Leontsev 1 , Richard Eitel 1
1 Chemical and Materials Engineering, University of Kentucky, Lexington, Kentucky, United States
Show AbstractBismuth ferrite BiFeO3 material is known for its multiferroic properties simultaneously exhibiting ferroelectric and weak ferromagnetic behavior, and it has been extensively studied in thin film as well as in bulk forms. However, bulk perovskite BiFeO3 has been difficult to obtain due to presence of secondary phases. Additionally, low DC resistivity prevents observation of ferroelectric switching in bulk BiFeO3. Incorporation of barium titanate BaTiO3 into solid solution with BiFeO3 was proposed to stabilize the perovskite structure and improve electrical properties. Improved dielectric losses and higher DC resistivity have been also achieved in bulk BiFeO3 by doping with Mn. In the current work, the Mn-modified bulk BiFeO3-BaTiO3 system has been studied as a potential lead-free piezoelectric material.BiFeO3-BaTiO3 ceramics of various compositions were prepared via solid-state route and pure perovskite phase was confirmed by X-ray diffraction. Addition of Mn has improved DC resistivity by 1 to 5 orders of magnitude (7.6x10^12Ωm vs 2.7x10^7Ωm for 25mol% BaTiO3 at RT) and significantly decreased dielectric losses. Polarization hysteresis measurements indicated “hardening” effect with increasing BaTiO3 content. Highest strain response has been observed in samples with ~33mol% and low-field piezoelectric d33 coefficient of 116pC/N is reported for 25mol% BaTiO3 composition. Temperature dependent phase transition behavior was investigated by differential scanning calorimetry (DSC) and dielectric constant K(T) measurements revealing depolarization temperatures higher than 400°C for the above mentioned compositions (25-35mol% BaTiO3). It is expected that with continued processing improvements and composition modification the BiFeO3-BaTiO3 system will form the basis of an important family of high performance lead-free piezoelectric ceramics.
9:00 PM - F3.30
Synthesis and Size-Dependent Ferroelectric Ordering of Colloidal GeTe Nanoparticles.
Mark Polking 2 , Haimei Zheng 3 1 , Jeffrey Urban 4 , Delia Milliron 4 , Christian Kisielowski 1 , Marissa Caldwell 6 , Simone Raoux 9 , Joel Ager 5 , Ramamoorthy Ramesh 2 8 , Paul Alivisatos 3 7
2 Department of Materials Science and Engineering, University of California, Berkeley, Berkeley, California, United States, 3 Department of Chemistry, University of California, Berkeley, Berkeley, California, United States, 1 National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 4 Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 6 Department of Electrical Engineering, Stanford University, Stanford, California, United States, 9 , IBM Almaden Research Center, San Jose, California, United States, 5 Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 8 Department of Physics, University of California, Berkeley, Berkeley, California, United States, 7 , Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractWhile the ferroelectric properties of oxide materials have been widely explored in both bulk crystals and thin-film nanostructures, the ferroelectric properties of the IV-VI semiconductors are relatively poorly understood, and studies of ferroelectric ordering in colloidal nanoparticles are nearly non-existent. In this study, we examine the synthesis and size-dependent ferroelectric ordering of colloidal nanoparticles of the simplest known ferroelectric GeTe, a IV-VI semiconductor that undergoes a displacive transition from a cubic rock salt structure to a polar rhombohedral structure below 625 K. Nanoparticles with average diameters of 8, 17, 100, and 500 nm with size distributions of 10-15 percent have been prepared using colloidal chemistry techniques. Characterization of these particles with x-ray diffraction indicates that particles of all sizes are phase-pure and have the rhombohedral structure characteristic of the low-temperature ferroelectric phase. Direct analysis of single nanoparticles of the smallest size (8 nm) using exit wave-reconstructed images taken with aberration-corrected transmission electron microscopy with sub-angstrom resolution provides further evidence of this distortion. Detailed in-situ synchrotron powder x-ray diffraction studies demonstrate a reversible rhombohedral-to-cubic structural phase transition in particles as small as 8 nm in diameter and indicate a systematic decrease in the magnitude of the angular distortion as a function of particle size. Temperature-dependent Raman experiments also reveal pronounced softening of both phonon mode peaks with increasing temperature characteristic of a displacive ferroelectric phase transition.
9:00 PM - F3.31
(001), (101), (111)-Single-oriented Epitaxial Pb(Zr,Ti)O3 Films Grown on CaF2 Substrates and their Characterization.
Satoru Utsugi 1 , Takashi Fujisawa 1 , Yasutaka Ehara 1 , Tomoaki Yamada 1 , Shintaro Yasui 1 , Hitoshi Morioka 1 2 , Takashi Iijima 3 , Hiroshi Funakubo 1
1 Department of Innovative and Engineered Materials, Tokyo Institute of Technology, Yokohama, Kanagawa, Japan, 2 Application Laboratory, Bruker AXS, Yokohama, Kanagawa, Japan, 3 Research Center for Hydrogen Industrial Use and Storage, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki, Japan
Show AbstractGrowth of the Pb(Zr,Ti)O3 [PZT] single crystal have been expected due to their large piezoelectric property. However, the growth of is known to be difficult for the existence of non-180o domain. Some groups reported to growing polar-axis-oriented PZT thin films below 200 nm, but there is few report on its thick film or single crystal. We reported on the successful growth of thick epitaxial PZT films with polar-axis-orientation. PZT thick films on (100)cSrRuO3//(100)LaNiO3//(100)CaF2 substrate by metal organic chemical vapor deposition(MOCVD) and estimated the crystal structure and electric property.1 Their property was in good agreement with theoretically predicted value.1, 2 In the present study, we succeed to grow (001), (101), (111) single-oriented epitaxial PZT films about 100 nm in thick on (100)cSrRuO3//(100)CaF2, (110)cSrRuO3//(111)CaF2, and (111)cSrRuO3//(111)Pt//(111)CaF2, respectively, for the Zr/(Zr+Ti) ratio of 0.35. This was different from the mixture phase of (001)/(100), (101)/(110) and (111) on (100), (110) and (111) SrRuO3//SrTiO3 substrates.The P-E hysteresis loops of the Pb(Zr0.35,Ti0.65)O3 had square shapes and well saturated. Remanent polarization of (001), (101), (111)-oriented PZT films were 85, 55, 50 μC/cm2, respectively. The estimated Ps value taking account of the tilting angle of the polar axis along the electric field direction were 85, 80, 89 μC/cm2 for (001), (101), (111)-oriented PZT films, respectively. These values are almost in good agreement with previously reported one for (001)-single oriented PZT films. This opens the possibility to check the systematic orientation dependency of the PZT properties. Ref. 1) T. Fujisawa et al., Appl. Phys. Exp. 1 (2008) 085001. 2) T. Fujisawa et al., J. Appl. Phys. 105 (2009) 061614.
9:00 PM - F3.32
Structural Characterization Of Cu2+ Functional Centers In `Lead-Free’ (K0.5na0.5)NbO3 Piezoelectrics.
Ebru Erunal 1 , Ruediger Eichel 1 , Jerome Acker 2 , Hans Kungl 2 , Michael Hoffmann 2
1 Ins. f. Phys. Chem., University of Freiburg, Freiburg i.Br. Germany, 2 University of Karlsruhe, Institute of Ceramics in Mechanical Engineering, Karlsruhe Germany
Show AbstractThe volatile and toxic nature of PbO in PZT (Pb(ZrxTi(1-x))O3) ceramics causes not only health but also environmental problems as being disposal and even during their processing. Therefore, even though these ceramics are widely used in piezoelectric transducers, transformers, sensors and etc., lead-free alternative materials have been currently investigated. Among these alternatives, the alkali niobate ferroelectrics ((K0.5Na0.5)NbO3, KNN) have been reported as one of the most promising materials due to their high Curie Temperature and electrical properties. In order to obtain dense compounds with decent properties, doping with different elements has to be performed. Although the use of copper-containing sintering aids seems a mandatory prerequisite for the realization of KNN-based devices, the exact impact of aliovalent Cu2+-doping on the KNN defect structure has remained unclear. The aim of this study is to figure out the structure of Cu2+ doped KNN ceramics via different EPR techniques since these dopants show paramagnetic characteristics. The results show that copper is incorporated as an acceptor-type center on the perovskite B-site and for reason of charge compensation two kind of mutually compensating defect dipoles are formed.
9:00 PM - F3.33
Lead-free Piezoelectric Thin Films in KNN and BNT-based Systems.
Maryam Abazari 1 , Ahmad Safari 1
1 Glenn Howatt Electroceramics Laboratories, Dept. of Materials Science and Engineering, Rutgers University, Piscataway, New Jersey, United States
Show AbstractWe have studied the deposition, ferroelectric and piezoelectric properties of two newly-developed lead-free compositions namely KNN-LT-LS and BNT-BKT-BT using pulsed laser deposition (PLD). It was revealed that in both compositions, high oxygen pressure (PO2 > 300mTorr) and deposition temperature (>700oC) are required in order to suppress the evaporation of volatile elements, namely K and Bi, and to improve the electrical properties. In pure KNN-LT-LS thin films with 450 nm thickness, high leakage current was observed which prohibited polarization saturation in the films. Effects of several acceptor and donor dopants including Ba, Mn and Ti have been studied in order to decrease the leakage current and improve the polarization. Mn-doping showed to effectively reduce the leakage and significantly enhance remanent as well as saturated polarization. 1mol% Mn-doped KNN-LT-LS thin films show 15 and 23 μC/cm2 remanent (Pr) and saturated (Psat) polarization, respectively. Dielectric constant and loss tangent of the films were approximately 750 and 0.08 at 1 kHz. BNT-BKT-BT films, On the other hand, show a very high Pr and Psat of 30 and 50 μC/cm2 which are more than twice as high as Mn-doped KNNLTLS films. Also, dielectric constants and loss of the BNT-BKT-BT films were very much comparable to or slightly higher than those of the KNN-LTLS film. In terms of piezoelectric properties, our d33 measurements using piezoresponse force microscopy (PFM) revealed that BNT-BKT-BT films also show a similar piezoelectric coefficient to 60 pm/V in KNN-LT-LS films. However, BNT-BKT-BT films show a very high coercive field of >80 kV/cm as compared to 20 kV/cm in KNN-LT-LS films. The lower properties of the KNN-LT-LS films as compared to the BNT-BKT-BT films are associated with the loss of potassium which is substantially higher in KNN-LTLS composition.
9:00 PM - F3.34
Preparation of PLZT Thin Films by Chemical Solution Deposition and Their Characterization.
Burkan Kaplan 1 , Ahmet Ozenbas 1
1 Metallurgical and Materials Engineering, Middle East Technical University, Ankara Turkey
Show AbstractIn this study, La3+ was substituted into lead zirconate titanate (PZT) system by Pb1-xLax (ZryTi1-y)1-x/4O3 nominal stochiometry and it was processed via chemical solution deposition on (111)-Pt/Ti/SiO2/Si-(100) substrates. A systematic study was carried out in different regions of PLZT phase diagram to obtain optimized results of ferroelectric, dielectric and optical properties of the material. The effects of sintering temperature and lanthanum modifications were investigated with regard to phase development, microstructure, and ferroelectric and dielectric characteristics. The electrical and optical properties such as hysteresis curves, dielectric constant, dielectric loss and optical transmittance of the films were obtained. The dielectric constant at morphotropic boundary is large compared to the other the other phases. Relative dielectric constants of Pb(Zr0.52Ti0.48)O3 and Pb0.95La0.05(Zr0.52Ti0.48)0.9875O3 films at 1 kHz were 431 and 230, respectively, and the loss tangent values were 0.2 and 0.061, respectively. Decrease in dielectric constant upon addition of La content was also observed in rhombohedral region. For the tetragonal region, maximum dielectric constant was reached at 10 %La content as 287.Ferroelectric properties of PLZT thin films such as remanent polarization (Pr) and coercive field (Ec) were investigated as a function of sintering temperature.Remanent polarization of the thin films were 0.56 μc/cm2, 6.194 μc/cm2, 6.94 μc/cm2 and 10.49 μc/cm2 as the sintering temperatures were 600 0C, 650 0C, 700 0C and 750 0C, respectively. The compositional change of ferroelectric properties are similar to dielectric properties. Remanent polarization showed a peak value then decreased while lanthanum content was increased in the tetragonal region of the PLZT phase diagram. For the other two crystal structure rhombohedral and on the morphotrophic phase boundary, slim hysteresis loops were obtained. Optical properties of PLZT thin films on quartz substrate were obtained by using UV-VIS spectrophotometer. Many optical constants were measured by the modified envelope method. The refractive index of the 9/65/35 PLZT thin film was 1.96, the extinction coefficient was measured as 0.0093 and absorption coefficient was 1.85*10-4 (1/nm). The thickness of the film was calculated as 335 nm which was nearly the same for one layer thin film measured by cross-sectional SEM image. Band gap energy of the film was found as 3.1 eV.Fatigue behavior of PLZT thin films was also investigated at 50 kHz and ±15V. Furthermore, leakage current characteristics of the films were obtained at ±15V. It has been observed that as the La content of the film was increased, leakage current of the PLZT films decreased.
9:00 PM - F3.35
The Effect of Substrate Vicinality and Orientation on Ferroelectric Properties of Epitaxial BiFeO3 Thin Films.
Vilas Shelke 1 , V. Harshan 1 2 , Sushma Kotru 1 2 , Gunwoo Kim 1 , Arunava Gupta 1
1 Center for Materials for Information Technology, University of Alabama, Tuscaloosa, Alabama, United States, 2 Department of Electrical and Computer Engineering , University of Alabama, Tuscaloosa, Alabama, United States
Show AbstractBismuth ferrite (BiFeO3) has emerged as a new multifunctional material with concomitant presence of electric/magnetic ordering and optical response sustainable over a wide temperature range. Several studies have indicated that the ferroelectric properties of BiFeO3 thin films are intimately linked to its structure and morphology. We have systematically studied the structural and ferroelectric properties of BiFeO3 films as a function of substrate orientation, vicinality and film thickness. Epitaxial BiFeO3 thin films of variable thickness have been deposited using pulsed laser deposition on (100), (110) and (111)-oriented SrTiO3 substrates with low (0.10) and high (40) miscut angles. Using SrRuO3 as a bottom electrode and Pt top contact, all the films show saturated ferroelectric loops. However, remnant polarization, coercive field and leakage current vary depending upon the film orientation, miscut angle and film thickness. These variations have been correlated with the domain patterns for the films revealed through piezoelectric force microscopy. Detailed results on crystal structure, microstructure, and magnetic behavior will also be presented.
9:00 PM - F3.36
Effect of Strain and Multiphase Formation on the Ferroelectric Properties of Multiferroic Bi-Fe-O Thin Films.
Lourdes Salamanca-Riba 1 , Joon Hyuk Yang 1
1 Materials Science and Engineering, University of Maryland, College Park, Maryland, United States
Show AbstractIn recent years multiferroic material systems have been identified as essential materials for next generation memory and logic device applications which utilize coupling of magnetism and ferroelectricity. BiFeO3 has attracted great attention because it is an intrinsic multiferroic material which displays ferroelectricity and antiferromagnetism at room temperature. Recent studies in our group (and by others) showed that in the Bi-Fe-O system grown by PLD on STO substrates, there are several co-existing phases of different structure, composition, and electrical and magnetic properties[1]. The microstructural evolution of coexistence of BiFeO3 , α-Fe2O3 and γ-Fe2O3 nanocolumnar structure can be controlled by oxygen partial pressure and affects the relaxation of the misfit strain as well as the magnetic properties of the BFO films. The formation of second phases in the BiFeO3 films gives rise to strains that can influence the ferroelectric properties of these materials. Our previous piezoelectric force microscopy results show increased switching response in films with Fe2O3 phases compared to that in pure BiFeO3 films. In this work, we investigate the role of strain and composition variation at the boundary between the BiFeO3 domains and the Fe2O3 domains on the ferroelectric properties of these films.1. “Microstructural Characterization of Multiphase Formation in Bi-Fe-O Multiferroic Thin Films”, SH Lim, M. Murakami, S. Fujino, SQ Ren, M. Wuttig, I. Takeuchi, L. Salamanca-Riba, and W.L. Sarney, Advanced Functional Materials 17, 2594-9 (2007).
9:00 PM - F3.37
Investigation of the Pb Depletion in Single and Dual Pulsed Laser Deposited Epitaxial PZT Thin Films and Their Ferroelectric Characterization.
Devajyoti Mukherjee 1 , Tara Dhakal 1 , Robert Hyde 1 , Hariharan Srikanth 1 , Pritish Mukherjee 1 , Sarath Witanachchi 1
1 Physics, University of South Florida, Tampa, Florida, United States
Show AbstractPulsed laser deposition (PLD) technique offers unique advantages in the growth of thin films of multi-component materials such as PZT (PbZr0.52Ti0.48O3). However, due to the high volatility of Pb, ablation of stoichiometric PZT targets causes preferential evaporation of Pb from the target at low laser fluencies. In addition, Pb depletion in films were observed for typical growth temperatures of 500oC to 600oC. This Pb deficiency is responsible for the coexistence of a pyrochlore phase with the perovskite PZT phase, degrading the ferroelectric properties of the films. To compensate for the Pb loss it is a general practice to add excess PbO during the preparation of the dense ceramic PZT targets. Our investigations have shown that the preferential evaporation of Pb from target is suppressed at high laser fluencies, but with the accompanying increase in the undesirable particulate density. In this paper we present a systematic study of the PZT target-laser interaction for both single laser and dual-laser ablation methods. The study includes films deposited from a stoichiometric PZT target and a PZT target with 30 at.% excess PbO. The films were deposited on single crystal MgO[100] and SrTiO3[100] substrates at 550oC with a background oxygen pressure of 500 mT. Single laser deposited films at a laser fluence of 5J/cm2 produced the highest Pb content while dual-laser ablated films where an excimer and a CO2 pulsed lasers were synchronized for ablation produced high Pb content for a an excimer laser fluence of less than 2J/cm2 . This enabled the growth of particulate-free PZT films with high Pb content that produced enhanced ferroelectric properties. Emission spectroscopy and time-gated ICCD imaging of the plasma plume showed variations in the Pb expansion profiles at different laser fluencies that correlated well with the Pb content observed in the deposited films. A correlation between the ablation conditions and the characteristics of the P-E hysteresis loops will be presented.
9:00 PM - F3.38
Antiferroelectric and Ferroelectric Phases in Strained PbZrO3.
Liwen Wan 1 , Scott Beckman 1
1 Material Science and Engineering, Iowa State University, Ames, Iowa, United States
Show AbstractThe antiferroelectric orthorhombic (AFE-O), ferroelectric tetragonal (FE-T), and ferroelectric rhombohedral (FE-R) phases of PbZrO3 (PZO) are studied under epitaxial strain and isotropic dilatation. The AFE-O phase is found to be the ground state of the unstrained crystal, in agreement with previous observations. The lattice parameter of the AFE-O basal plane is approximated by averaging the Pb-Pb spacing, and is found to be 0.58 nm. It is determined that the FE-T phase becomes the preferred phase when the basal lattice parameter is 0.39 nm, which corresponds to an isotropic epitaxial strain of -4.8 %. The relative stability of phases is studied under an isotropic dilatation. The phase stability is mapped as a function of crystal density, ranging from 6.7 to 7.4 g/cm-3.
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Elastic Strain Evolution in Polycrystalline BaTiO3 Ceramics using Synchrotron X-ray Diffraction.
Goknur Tutuncu 1 , Mesut Varlioglu 1 , Ulrich Lienert 2 , Jon Almer 2 , Ersan Ustundag 1
1 Materials Science and Eng., Iowa State University, Ames, Iowa, United States, 2 , Advanced Photon Source, Argonne National Laboratory, Chicago, Illinois, United States
Show AbstractFerroelectric materials are elastically anisotropic and exhibit additional anisotropy after domain switching. Extensive sets of data were collected under mechanical loading to quantify response of polycrystalline ferroelectric BaTiO3. In-situ high energy X-ray diffraction experiments were conducted via a four-point bending fixture in transmission geometry and a two-dimensional detector. Lattice strain and texture evolution (domain switching) were measured in multiple sample directions simultaneously. Diffraction data analysis methods such as single peak fitting and the whole-pattern Rietveld method were used and experimental results were compared to elastically computed strain under the constant stress (Reuss) approximation and macroscopic bulk response. Lattice strains from the (002)-(200) planes showed significant anisotropy at the tensile and compressive parts of the bending sample whereas the (111) lattice strains did not. Significant texture evolution (domain switching) observed at high load levels and usually the most considerable changes were observed in twin reflections (or doublets) due to non-180° domain switching coupled with lattice strain evolution. Moreover, electrical poling effects onto the non-180° domain switching were investigated with prepoled specimens that experienced higher strain and texture compared to those in unpoled samples. This study also involved methodology development to properly measure and interpret highly anisotropic lattice strain data; its results will be described briefly.
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Microstructural and Magneto-electric Properties of Pulsed Laser Deposited Ferroelectric/Ferromagnetic Heterostructures.
Ricardo Martinez 1 , Ratnakar Palai 1 2 , Ram S. Katiyar 1 2
1 Physics, University of Puerto Rico, San Juan PR, Puerto Rico, United States, 2 Institute for Functional Nanomaterials, University of Puerto Rico, San Juan , Puerto Rico, United States
Show AbstractA series of multiferroic heterostructures using a ferromagnetic La0.7Sr0.3MnO3 (LSMO) and a ferroelectric Ba0.7Sr0.3TiO3 (BST) were grown on MgO (100) substrates with LaNiO3 (LNO) as a bottom electrode by pulsed laser deposition (PLD). The crystal structure, phase purity, and orientation of the thin films characterized by X-ray diffraction showed a high orientation of (110) phase because to arrangement of LNO cells on the MgO substrate. Surface morphology was investigated by atomic force microscopy (AFM). The dielectric properties of multilayers were studied as a function of temperature (100-400 K) and frequency (1 KHz-1 MHz). Ferroelectric Hysteresis measurements at room temperature showed that polarization from superlattices is small compared to typical polarization of single layer ferroelectric BST. The dielectric relaxation of heterostructures was studied using Maxwell-Wagner model. The observation of magnetic Hysteresis loop at room temperature implies no obvious degradation of LSMO layer after BST deposition. Keywords: superlattice, multilayer, ferroelectric, ferromagnetic, Maxwell-Wagner Model.
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Textured Sol Gel BiScO3-PbTiO3 Thin Films On LaNiO3.
Paula Vilarinho 1 , Jingzhong Xiao 1 , Aiying Wu 1
1 Dep. of Ceramics and Glass Engineering, University of Aveiro, Aveiro Portugal
Show Abstract(1-x)BiScO3-xPbTiO3 have attracted considerable attention for applications in microelectromechanical systems, ultrasonic and actuation devices in high temperature environments [1]. Compared to the Pb(Zr,Ti)O3 (PZT), morphotropic phase boundary (MPB) (1-x)BiScO3-xPbTiO3 system exhibits a high Curie temperature (Tc) of about 450 oC and comparable piezoelectric properties to those of relaxor-PbTiO3, meeting the exigent requirements for piezo/ferro-electrics with high-Tc to be used in the automotive, military and aerospace industries.In previous works of the present authors, improved dielectric/ferroelectric properties of MPB BSPT films were obtained via the use of a PbTiO3 seed-layer [2], or IrO2 oxide electrodes [3]. However these films are randomly oriented. To grow thin films with a high degree of orientation and further optimize the electrical properties of sol-gel derived MPB 0.37BiScO3-0.63PbTiO3 (BSPT) thin films, LaNiO3 (LNO) was introduced between the substrate and the ferroelectric film as a structural template, bottom electrode and buffer layer, due to its good conductivity and structural match with BSPT. BSPT films on LNO are highly (100)-texture oriented and exhibit a columnar growth. In comparison to the films on Pt electrodes, the use of LNO electrodes favours considerably the electrical properties. BSPT films on LNO exhibit a dielectric constant of 2500 and dielectric loss of 0.02, a remanent polarization of 40 μC cm-2 and a coercive field (Ec) of about 68 kV cm-1. Particularly, the use of LNO enhanced the piezoelectric coefficient to 200 pm/V. LNO improved the fatigue behaviour of BSPT films as well. BSPT films on LNO show no macroscopic fatigue till 1010 switching cycles. At the microscopic level, PiezoForce Response Microscopy indicates that BSPT thin films on LNO do not apparently show local fatigue till 109 switching cycles, while films on Pt show obvious local fatigue at 1.5×108 cycles. The role of the film / electrode interface on the film orientation and improvement of the electrical performance of BSPT thin films is presented and discussed.References[1] T. Yoshimura, Appl. Phys. Lett., 2002, 81, 2065.[2] J. Xiao, A. Wu, P. M. Vilarinho, Appl. Phys. Lett., 2008, 92, 032902.[3] J. Xiao, A. Wu, P. M. Vilarinho, J. Mater. Chem., 2009, DOI: <10.1039/B900970A>, in press.
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Liquid Injection MOCVD Growth of BiFeO3 Thin Films on GaN.
Tahir Zaidi 1 , Muhammad Jamil 1 , Andrew Melton 1 , Ian Ferguson 1
1 School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractThe multiferroic properties of BiFeO3 along with its high Curie and Neel temperatures make it a strong candidate use in magneto-electric device applications. The growth of BiFeO3 has been carried out by various techniques; however due to non-availability of a high volatility Bi precursor, there are very few reports of MOCVD growth. Similarly growth of BiFeO3 films directly on GaN has not been very successful due to the large lattice mismatch. In this paper we report successful growth of BiFeO3 thin films by liquid injection MOCVD on multiple substrates including GaN. The precursors used for liquid injection were Bi(thd)3 and Fe(thd)3 dissolved in THF. Growths were carried out at 700°C using O2 as reactive gas and N2 as process gas. Post growth annealing at 800°C was done in air to achieve poly-crystalline BiFeO3 thin films. The resulting films were characterized for their structural, optical, magnetic and electrical properties by atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray diffraction (XRD), photoluminescence (PL), optical transmission, vibrating sample magnetometry (VSM) and Hall Effect measurements.
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Planar-MIM Capacitors using Barium Strontium Titanate (BST) Thin Films for Frequency Agile Devices.
Peter Lam 1 , Zhiping Feng 2 , Michael Steer 2 , Jon-Paul Maria 1
1 Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina, United States, 2 Electrical and Computer Engineering, North Carolina State University, Raleigh, North Carolina, United States
Show AbstractThe two commonly used BST capacitor configurations are metal-insulator-metal (MIM) and planar interdigitated fingers (IDC). MIM capacitors exhibit higher capacitance density and tunability as most of the electric field is confined to the dielectric, while in IDC capacitors some of the field propagates through the air and the substrate, thus lowering the overall capacitance and tunability. In this presentation we explore the geometric limits of tuning and capacitance of small value IDC capacitors, and demonstrate a new planar capacitor configuration aimed at reducing the amount of parasitic field. These abilities are important for producing ferroelectric capacitors that access frequencies above 10 GHz.We will present a data set for of capacitance vs. gap length for a set of simple gap capacitors with a constant gap width of 3 µm and variable gap length. Capacitance scales linearly with gap length, but tunability does not. We show that when the gap length and the width become similar, the non-tunable fringe capacitance contribution predominates. Consequently for tunability, and applicability to high frequency, is geometrically limited.To overcome this situation, we propose an inverted structure where the IDC fingers are patterned on the bare substrate and the dielectric is deposited on top. Our proposed stack consists of a sapphire substrate, interdigitated platinum electrodes with a thin titanium adhesion layer, followed by an epitaxial sputtered BST film. We refer to this structure as a planar MIM (pMIM).The presentation will detail the synthesis conditions required to integrate a metal electrode layer that is compatible with the high temperature deposition of the dielectric. This includes an e-beam deposited platinum (100 nm) with a 1 nm titanium adhesion layer that can sustain a BST deposition temperature up to 750 °C without thermo mechanical failure. Ba0.7Sr0.3TiO3 films are optimized by RF magnetron sputtering on (0001) sapphire at a deposition temperature of ~ 700 °C with and without any post anneals. X-ray diffraction analysis and electrical characterization reveal heteroepitaxial BST that exhibits 60% dielectric tunability at a ~ 450KV/cm dc field in a conventional IDC.Finally we demonstrate a fully integrated BST pMIM capacitor. We will present SEM micrographs of the fully processed cross section showing structural stability of all layers. Preliminary electrical characterization of the inverted structure shows a tunability of 30% with a 175 KV/cm field, for this effective field, tunability is larger than observed for the conventional structure. Results from further optimization will be presented including the scaling of tunability with gap width and gap length.
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Enhancement in Ferroelectricity in V Doped ZnO Thin Film Grown using Laser Ablation.
Tara Dhakal 1 , Devajyoti Mukherjee 1 , Robert Hyde 1 , Srikanth Hariharan 1 , Pritish Mukherjee 1 , Sarath Witanachchi 1
1 Physics, University of South Florida, Tampa, Florida, United States
Show AbstractWe report evidence of enhancement in ferroelectricity in thin films of vanadium (V) doped ZnO. V doped ZnO thin films show ferroelectricity due to the strain in the Zn-O bond where the Zn site is replaced by the smaller size V ion. The ferroelectricity in V doped ZnO is enhanced by growing the films at higher oxygen pressure. This process reduces oxygen deficiency and the material becomes very insulating, which in turn lowers the leakage current through the ferroelectric capacitor. To fabricate a ferroelectric device, first a 300 nm thick conducting ZnO layer as the bottom electrode was grown epitaxially on c-cut sapphire (Al2O3) (0001) at a growth temperature of 600°C and at an oxygen pressure of 10mtorr by the pulsed laser ablation technique, followed by 2 at. % V doped ZnO layers, with thickness of around 1 μm. X-ray analysis showed the layers to be epitaxial where the (0002) diffraction peak had a FWHM below 1°. The epitaxial V-doped ZnO films were grown under different oxygen pressure from 100 mtorr to 500 mtorr. The films with higher oxygen pressure are more insulating than the one grown with lower oxygen pressure. The saturation polarization doubled when the growth pressure increased from 300 mtorr to 500 mtorr. To further reduce the oxygen deficiency and produce defect free crystalline film a dual laser ablation system will be used in which a CO2 laser is added to the excimer KrF laser in synchronization for the ablation of targets. In addition, results on 5 at. % and 10 at. % V doping will be presented.
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Potassium Niobate Thin Films Deposited on Metal Substrates for use as Biocompatible Ferroelectric Implants.
Jason Stoker 1 , Ashutosh Tiwari 1
1 Materials Sciance and Engineering, University of Utah, Salt Lake City , Utah, United States
Show AbstractCurrently there is a great research thrust towards finding environmentally friendly lead free replacements for PZT. One such material that is receiving attention for this purpose is potassium niobate. Presently potassium niobate (KNbO3; KN) and materials based on it are being studied due to their large nonlinear optical coefficients, electro-optic coefficients, and piezoelectric constants. The components of potassium niobate are known to be biocompatible. In this study the advent of using KN as an implantable ferroelectric was explored. In this work thin films of KN were made via pulsed laser deposition on numerous substrates, including single crystal ceramics and non noble metal substrates. The substrates examined were silicon (111), (100), lanthanum aluminum oxide (LaAlO3(100)), magnesium oxide (MgO (100)), niobium doped strontium titanate (Nb:STO (100)), copper, cobalt, nickel, titanium, niobium, tantalum, molybdenum, and single crystal molybdenum. The thin films were analyzed using XRD, SEM, FTIR, bandgap measurements, and polarization vs electric field (P-E). XRD showed high orientation of the films deposited on single crystals. The films deposited on the metal substrates lacked orientation while still maintaining good ferroelectric behavior through P-E measurements. A max polarization of 9.4 μC/cm2 was measured on the copper substrate film, with similar results for the other metal substrates. Biocompatibility tests were performed on both bulk KN and several films deposited on known biocompatible metal substrates including molybdenum, titanium, and niobium with promising results.
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Strain Relaxation and Critical Thickness in BaTiO3 Thin Films on GdScO3 Substrates.
Yi Zhang 1 , Christopher Nelson 1 , Michael Katz 1 , Tao Hang 1 , Charles Brookes 2 , Darrell Schlom 3 , Xiaoqing Pan 1
1 Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States, 2 Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania, United States, 3 Materials Science and Engineering, Cornell University, Ithaca, New York, United States
Show AbstractIt is well established that ferroelectric thin film properties can be improved by the application of global strain due to film-substrate lattice mismatch. However, the thickness of a coherent film cannot exceed a critical value (hc) beyond which the film strain begins to relax. In this work we experimentally determine the critical thickness value in ferroelectric BaTiO3 thin films compressively strained on (110) GdScO3 substrates (f = -0.476%) and compare the results to two of the predominant theoretical models. Two series of BaTiO3 films were grown with thicknesses of 8 nm, 16 nm, 32 nm, and 64 nm by reactive molecular-beam epitaxy. One series was as-grown, another was subsequently annealed at 1000°C degrees for 2 hours in an oxygen ambient. Transmission electron microscopy revealed that above the critical thickness both series are relaxed by the formation of a<100>BaTiO3 dislocation network. For the as-grown films this relaxation occurred between 32 nm and 64 nm. Relaxation in the annealed series occurred between 8-16 nm. This shows the as-grown films are not at thermodynamic equilibrium and metastable strained films above the critical thickness can be obtained. The two predominant critical thickness models use either mechanical equilibrium (Matthews and Blakeslee) or energy equilibrium (People and Bean) to calculate hc. Applied to this system the MB model estimates a critical thickness of 8 nm whereas the PB model estimates it to be 360 nm. Therefore, in this particular system the MB model appears to be a much better predictor for critical film thickness
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Effect of Epitaxial Strain on the Magnetoelectric Coupling of Lattice Mismatched YMnO3 Thin Films Grown on Sapphire (0001) Substrate with Conducting Zn0.99Ga0.01O Bottom Contact.
Anil Singh 1 , Michael Snure 2 , Ashutosh Tiwari 2 , S. Patnaik 1
1 School of Physical Sciences, Jawaharlal Nehru University, New Delhi, Delhi, India, 2 Department of Materials Science and Engineering, University of Utah, Salt Lake City, Utah, United States
Show AbstractMultiferroic materials that exhibit simultaneous magnetic, ferroelectric and ferroelastic order parameters have recently attracted renewed attention because of their coupled order parameters and their potential for cross electromagnetic functionality. We report synthesis of highly c-axis aligned thin films of multiferroic YMnO3 on Sapphire substrate with Zn0.99Ga0.01O (ZnGaO) as a conducting buffer layer. The lattice parameters for hexagonal YMnO3 and ZnO are a = 3.06 A and c = 3.25 A respectively, with a lattice mismatch of 5.8%. YMnO3 and ZnGaO films were deposited on sapphire substrate by pulsed laser deposition technique starting from high purity single phase bulk targets prepared using a low temperature sol-gel technique. The prepared films were characterized by XRD, SEM, and EDAX that confirmed highly c-axis oriented nature of the film. We have done temperature and magnetic field dependent dielectric measurements which indicate an anomaly in dielectric constant ε (T) and tand, in the vicinity of 30 K, well below the Néel temperature ~ 70 K of bulk YMnO3. This anomaly in ε (T) and tand and its magnetic field dependence is attributed to influence of strain due to lattice mismatch between the substrate and the lattice parameters of YMnO3 film. The inverse S - shape anomaly in loss factor which is the signature of antiferromagnetic transition temperature shifts to ~ 30 K as compared to bulk YMnO3 which is at ~ 70 K. SQUID measurement confirmed that the antiferromagnetic temperature of the film is ~ 30 K. The ferroelectric behavior of the YMnO3 films was confirmed by room temperature capacitance-voltage (C-V) characteristics and the butterfly nature of the C-V curves suggest ferroelectric behavior at room temperature. Our results show that it is possible to tune the multiferroic property via changes in ferroelastic route.
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Misfit Strain Relaxation by Secondary Phase Formation in Multiferroic BiFeO3 Epitaxial Thin Films.
Yinlian Zhu 1 , Xue Wang 1 , Xiuliang Ma 1
1 Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang China
Show AbstractBiFeO3 has been widely investigated due to its intrinsic multiferroic properties. It is recently shown that parasitic phases coexisting in BiFeO3 thin films influence the magnetic properties of the films and also change the misfit relaxation behavior in the thin films. By varying the deposition oxygen pressure, the main phase formed in the films changes from single phase of BiFeO3 to α-Fe2O3+BiFeO3 or a mixture of BiFeO3, α-Fe2O3 and γ-Fe2O3.In this abstract, we report the growth of BiFeO3 thin films on SrRuO3-coated SrTiO3 substrates at different oxygen pressures (1pa and 0.3pa) by laser MBE technique and the microstructures were characterized by means of transmission electron microscopy. The deposition temperature was kept at 823 K. Contrast analysis and electron diffraction patterns indicate that the as-received thin films are epitaxially grown on SrRuO3-coated SrTiO3 (100) substrates. The thin films consist of single phase BiFeO3 embedded by the secondary phase of α-Fe2O3. The secondary phase is not randomly distributed within the matrix but shows regular configurations with boundaries preferred along (102)α and (1-12)α planes. The α-Fe2O3 phase has definite orientation relationships with the BiFeO3. By lowering the oxygen pressure, the density and the size of α-Fe2O3 phase increases whereas the regularity decreases. High resolution transmission electron microscopy observation on a large view area shows that less misfit dislocations can be identified along the interfaces between the films and the substrates. The reason may lie in that the distance between adjacent misfit dislocations is large and thus the density of misfit dislocations is quite low; In other words, misfit dislocation formation in this heteroepitaxial system is not a major strain relaxation mechanism as it is usually the case in other perovskite epitaxial thin films. It is proposed that the secondary phase formation in these systems may contribute much to the relaxation procedure. Based on TEM observation, it is suggested that the density and the size of the secondary phase can be controlled through varying oxygen pressure. By controlling the ratio of BiFeO3 and Fe2O3, multiferroic nanocomposite thin films with various properties could be obtained.This work is supported by the National Natural Science Foundation of China (No.50871115).
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High-resolution X-ray Diffraction Study of PZN-PT Single Crystals.
Wei-Sea Chang 1 , Leong-Chew Lim 1 , Ping Yang 2
1 Mechanical Engineering, National University of Singapore, Singapore Singapore, 2 Singapore Synchrotron Light Source, National Univeristy of Singapore, Singapore Singapore
Show AbstractHigh-resolution synchrotron x-ray diffraction (HR-XRD) (002)pc reciprocal space mappings have been performed on both unpoled and poled relaxor ferroelectric PZN-(4.5-9)%PT single crystals, as a function of temperature and electric field. To avoid undesired surface effects produced by mechanical polishing, a fracturing technique was used to expose the relatively stress free crystal bulk for the HR-XRD study. Evidence for rhombohedral and tetragonal micro/nanotwins could be detected at room temperature for PZN-(4.5-8)%PT and PZN-9%PT, respectively. For PZN-(4.5-7)%PT, the room temperature rhombohedral phase exhibits an extremely broad diffraction in most instances, although {100}pc- and {110}pc-type R micro/nanotwin diffractions could be detected in a few cases. For PZN-9%PT, the room temperature phase consists predominantly of tetragonal {110}pc-type microtwins. The tetragonal micro/nanotwin behaves in a coordinated manner upon heating and poling. The effects of rhombohedral and tetragonal micro/nanotwins on the transformation behaviors of PZN-(4.5-9)%PT single crystals will be presented and discussed. Also discussed are the effects of temperature and applied electric field on the phase stability and phase transformation paths of this material.
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Fabrication and Characterization of Artificially Designed PZT/LSMO Multiferroics Heterostructure.
Sandra Dussan 1 , Ashok Kumar 1 , Ram Katiyar 1
1 Physics and Institute for Functional Nanomaterials, University of Puerto Rico, San Juan, Puerto Rico, United States
Show AbstractMultiferroics materials are a class of functional material that combines two or more functional properties i.e. ferromagnetism, ferroelectricity and ferroelasticity. Since there are very few single-phase magnetoelectric multiferroic materials exhibit in nature, which have simultaneously more than one ordered parameters. The recent finding of multiferroic composite and layered nanostructure with the coexistence of ferroelectric and ferromagnetic materials have attracted the attention of various researchers due to its potential applications in highly sensitive magnetic field sensors and multistate memory devices. Early experimental analysis on heterostructures comprising a ferro-or piezoelectric and a carrier-mediated magnet suggest the possibility of artificially engineered multiferroics in which the coupling is mediated through an electrostriction near interface. Synthesis and characterization of PbZr0.52Ti0.48O3/La0.67Sr0.33MnO3 (PZT/LSMO) heterostructure thin films with different periodicity were done over wide range of temperatures and frequencies. The layered structure were grown on conducting La0.5Sr0.5CoO3/LaNiO3 coated MgO (100) substrates using Pulsed laser deposition technique. The XRD patterns of PZT/LSMO multilayer films with different periodicity compared with the pure PZT and LSMO thin films grown at the same conditions evidenced that layered structure formed without any secondary phases. Phase purity was further confirmed by their respective Raman spectra. Surface topography showed well defined grain having average size less than 50 nm with surface roughness ~ 2-7 nm. Grain size and surface roughness changes with change of periodicity. Room temperature magnetization-field (M-H) exhibit well-shaped magnetization hysteresis loops, good saturation and low coercivity. Magnetic anisotropy was observed, further analyzed as function of film thickness and orientation. The electrical properties of hetrostructure will be discussed in context of film thickness and their periodicity. Magnetoelectric properties will be analyzed by magnetic force microscopy with different biased electric field.
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Interplay Between Structural and Magnetoelectric Properties and of La Substituted BiFeO3-PbTiO3.
Anupinder Singh 1 , Sanjay Mishra 2 , P. R. Krishna 2 , Ratnamala Chatterjee 1
1 Physics Department, Indian Institute of Technology Delhi, New Delhi, Delhi, India, 2 Solid State Physics Division, Bhabha Atomic Reseach Centre, Mumbai, Maharashtra, India
Show AbstractBiFeO3 (BF) is the only material known to exhibit both magnetic order (TN= 643 K) and ferroelectric order (ferroelectric transition temperature TcFE= 1103 K) at room temperature. However, the magnetoelectric coupling in BF is very weak (1, 2). Recently, detailed studies on the effect of large La substitution in (BF0.50–LF0.50 )0.50–(PT)0.50 , investigated by the authors(3) showed significantly improved polarization PS, magnetization M and magnetoelectric (M-E) coupling in this solid-solution. However, the complex mechanism of origin of PS and magnetization in (BF0.50–LF0.50 )0.50–(PT)0.50 still requires further probing. Neutron diffraction offers certain unique advantages over x-rays in the accurate determination of light elements (like oxygen atoms), subtle changes in structure and phase transitions associated with them. In this paper, we present the results of powder x-ray and neutron diffraction measurements in the range 25K≤T≤300K, in conjunction with detailed impedance spectroscopy, ac conductivity to clarify issues related to the origin of ferroelectric behavior observed in La rich (BF0.50–LF0.50 )0.50–(PT)0.50. A good fit of neutron diffraction data including the weak superlattice reflections between the observed and calculated profiles prove R3c (Sp. Gr. No. 161) structure of the sample and thus justifies ferroelectric nature(3). Impedance spectroscopy results clearly indicate the presence of both grain and grain boundary relaxation processes. The conducting grains and highly insulated grain boundaries result in a piling of charge at interfaces giving rise to large dielectric and polarization values at lower frequencies. However at higher frequencies the profile shows deviation from Maxwell-Wagner model. The calculated polarization showed a distinct change in the temperature range 150 – 200 K, suggesting the existence of a structural anomaly in this sample around this temperature. Interestingly dc magnetization (M), ac susceptibility and capacitance measurements showed changes around 170 K, suggesting M-E coupling in this temperature range, that is confirmed by Magnetocapcitance measurements.References:1C.Tabares-Munoz, J.P.Rivera, A. Monnier and H.Schmid, Japanese Journal of Applied Physics 24, 1051 (1985) 2S. V. Surynarayana, Bull. Mater. Sci. 17, 1259 (1994) 3Anupinder Singh, Arti Gupta and Ratnamala Chatterjee, Applied Physics Letters 93, 022902 (2008)
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Tunable Ferroelectric Properties of BaTiO3 Thin Films on Buffered Terfenol-D Substrates by Magnetic Field.
Junyi Zhai 1 , Jie Xiong 1 , Quanxi Jia 1
1 MPA-STC, Los Alamos National Lab, Los Alamos, New Mexico, United States
Show AbstractBaTiO3 thin films were grown on poly-crystal substrate Terfenol-D with an epitaxial buffer layer via pulsed laser deposition. Comparing to single crystal oxide substarte, Terfenol-D was cheap but had larger magnetostrictive property. Microstructural characterization showed that BaTiO3 thin films were epitaxial. The thickness of BaTiO3 thin film was about 200 nm. BaTiO3 films showed good ferroelectric feature. A large magnetoelectric response was observed in the multiferroic film-alloy composites. Besides the ferroelectric properties could be dramatically tuned by applied magnetic field.
9:00 PM - F3.55
Magnetic and Electric Properties of Rare Earth (La,Nd) Substituted BiFeO3 Nano Crystallites Multiferroic System.
Kuldeep Singh 1 , Ashish Gautam 1 , K. Sen 1 , R. Kotnala 2 , M. Singh 1
1 Deptt. Of Physics, Himachal Pradesh University, Summer hill, Himachal Pradesh, India, 2 National Physical laboratory, NPL Delhi, New Delhi, Delhi, India
Show AbstractIn recent years, more attention has been paid to multiferroic materials,which possess the combined properties of ferromagnetism, ferroelectric owing to their physical mechanism and have potential application for the design of multifunctional devices [1-3]. There is scarcity of materials exhibiting magnetoelectric behaviour at room temperature because the conditions for being simultaneously ferroelectric and ferromagnetic, empty and partially filled transition metal orbit [4, ] respectively; are in general mutually exclusive. The perovskite BiFeO3 (BFO) is one of the few known magnetoelectric multiferroic materials in which ferroelectric (Tc~830oC) and antiferromagnetic (AF) (TN~370 oC) order parameters coexist up to quite high temperature [5]. BiFeO3 is reported to have a rhombohedrally distorted perovskite structure belonging to space group R3c [6]. BiFeO3 bulk yields a six line Mössbauer spectrum at room temperature with a hyperfine field of 49.3T [7]. The major problem of BiFeO3 based material is low electrical resistivity. Recently, it has been shown that the space-modulated spin structure of BiFeO3 can be collapsed by the A-site substitution, resulting in a canted antiferromagnetic order, and A site Substitution can improve the electrical and magnetic properties. We prepared Bi1-xNdxFeO3 (x=0, 0.05, 0.1, 0.15, abbreviated as NBFO) and Bi1-xLaxFeO3 (x=0, 0.05, 0.1, 0.15, abbreviated as LBFO) nano ceramic samples by solution combustion technique [8] and investigated structural, magnetic and dielectric properties. Results indicate that the addition of Nd and La can improve significantly the ferromagnetic properties of BiFeO3 nano crystallite. Transmission electron microscope was used to confirm the particle size. Dielectric properties of samples were studied using Impedance analyser in frequency range 100 and 1MHz. The Mössbauer measurements were carried out using a standard PC-based spectrometer equipped with a Weissel velocity drive operating in the constant acceleration mode. The Mössbauer spectra are fitted with NORMOS-SITE program and the obtained hyperfine parameters are with respect to natural iron. Room temperature magnetization measurements were carried out using a Lakeshore 7400 series vibrating sample magnetometer (VSM). Results are discussed on the basis various theories and models. [1] W.Eerenstein, N.D. Mathur and J.F. Scott. Nature 442,759 (2006)[2] J. Hemberger, P. Lunkerheimer, R.Fichtl, Krug von Nidda H.A, V. Tsurkan and A.Loidl Nature 434 364 (2005)[3] T. Lottermoser T. Lonkal. U. Amann, D. Hohlweln, J Ihringer and M. Flebig Nature 430 541 (2004) [4] N. A. Spaldin and M. Figbig Science 309 391 (2005).[5] G. A. Smolankii and I. Chupis Sav. Phys-Usp. 25 475 (1982).[6] Yu.Ya Tomashpolskii, Yu.N. Venevtsev, G.S. Zhdanov, Sov.phys. Crystallogr. 12 209 (1967). [7] A. Biran, P.A. Montano, U. Shimony, J. Phys. Chem. Solids 32 327 (1971).[8] K. Singh, R. K. Kotnala and M. Singh, Appl. Phy. Lett. 93, 212902 (2008).
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Low Temperature Growth and Laser-Induced Phase Transformation of BaTiO3 Films for Uncooled IR Detector Applications.
Wendy Sarney 1 , Frank Livingston 2 , Daniel Morse 3 , John Little 1 , Krisztian Niesz 3 , Teyeb Ould-Ely 3 , Melanie Cole 4 , Mathew Ivill 4
1 Sensors & Electron Devices Directorate, U.S. Army Research Laboratory, Adelphi, Maryland, United States, 2 Micro/Nanotechnology Department, The Aerospace Corporation, El Segundo, California, United States, 3 Institute For Collaborative Biotechnologies, University of California, Santa Barbara , Santa Barbara, California, United States, 4 Weapons and Materials Research Directorate, U.S. Army Research Laboratory, Aberdeen Proving Ground, Maryland, United States
Show AbstractPyroelectric infrared (IR) detectors based on perovskite oxides are of interest in part because of their lack of need for cooling, which makes them relatively more affordable and operationally simpler than cooled photon detector systems. Using bio-inspired low-temperature nanoparticle deposition, direct-write laser phase conversion, and micro-electro-mechanical systems (MEMS) fabrication techniques, we are working towards an uncooled IR focal plane array (FPA) process compatible with monolithic integration of the detector pixels directly onto silicon readout integrated circuits (ROICs), substantially reducing the cost and increasing the yield over the currently used hybrid focal plane/readout circuit technology.Nanostructured thin film synthesis for many IR detector materials requires cost-intensive, high temperature techniques such as molecular beam epitaxy (MBE). Our more flexible and environmentally benign synthesis strategies are based on the principles of biomineralization. We use a novel vapor diffusion catalytic synthesis route from a bimetallic precursor that offers a very low temperature (16°C) pathway to BaTiO3 nanoparticles. This synthesis method is based on vapor phase delivery of water as catalyst in a temporally controlled gradient to promote the kinetically controlled growth of highly crystalline 6 nm nanoparticles. Smooth, crack-free films are deposited by spin-coating a sonicated solution of the functionalized nanoparticles onto PtTi/Si substrates.Following film deposition, the direct-write laser pulse modulation process induces site-selective and local phase transformation from the non-pyroelectric cubic phase to the pyroelectric tetragonal phase. Traditional thermal processing techniques lead to global phase transformations, where the entire deposited film undergoes structural conversion. For the laser pulse modulation process, the development of initial laser pulse scripts are based on temperature-dependent parameters, including the heat capacity, thermal diffusivity and conductivity, and optical absorption properties of the nanostructured thin-films.We will fabricate the samples into parallel plate capacitors by evaporating 100μm metal electrodes on top of the deposited pyroelectric film and measure the dielectric constant, ε, of the pre and post laser-treated films. ε is a critical component of the figure of merit FD for the use of pyroelectric materials as thermal detector elements. Our unique process of combining the low-temperature nanostructured thin-film growth and direct-write digitally-scripted laser phase transformation will allow the precision fabrication of patterned 2-D focal-plane arrays. Since our process steps do not subject the substrates to excessive temperatures or caustic chemicals, the films will be compatible with monolithic integration with ROICs.
9:00 PM - F3.57
Low-loss Multiferroic Fe3O4/BaTiO3 Core/shell Nanoparticles.
Yong Koo 1 , Byung Yun 1 , Jong Jung 1
1 Physics, Inha University, Incheon Korea (the Republic of)
Show AbstractTo overcome the hindrance of possible application of multiferroics in nano-scale, we have investigated the magnetoelectric coupling in ferroelectric and ferromagnetic composites, with a very special geometry, i.e., core/shell nanoparticles. The nanoparticles are consisted of highly-insulating ferroelectric BaTiO3 as a shell with a 50 nm thickness and semi-conducting ferrimagnetic Fe3O4 as a core with a 1 μm diameter. By combining the sonochemical and hydrothermal methods, we successfully obtained nearly mono-dispersed Fe3O4/BaTiO3 nanoparticle. Cross-section transmission electron and energy dispersive x-ray microscope measurements suggest the clear interface between core and shell. By measuring the electric polarization, dielectric constants under external magnetic field and the magnetization changes near the structural transition temperatures of BaTiO3, we confirm the strain-induced magnetoelectric couplings. Compared with BaTiO3/Fe3O4, the Fe3O4/BaTiO3 nanoparticles show very small electric loss.
9:00 PM - F3.58
Studies on the Dielectric and Ferroelectric Anisotropy of Layer-Structured Compounds Srn-3Bi4TiO3n+3 (n=5).
Shuo Jin 1 , Isabel Miranda Salvado 1 , Maria Elisabete Costa 1
1 Ceramic and Glass Engineering, CICECO, University of Aveiro, Aveiro Portugal
Show AbstractAurivillius oxides are bismuth layered perovskites (BLP) whose crystal structure comprises (Bi2O2)2+ layers interleaved by n perovskite-like slabs (An-1BnO3n+1)2- where n may vary from 2 to 8. BLP applications in modern electronics include capacitors, ferroelectric memories (non volatile (FRAMs), dynamic random access memories (DRAMs) and electromechanical systems. Since fatigue-free properties against repeated polarization switching were demonstrated in SrBi2Ta2O9 extensive literature reports were produced along the last decade for further properties improvements. Comparatively much less efforts have been put on BLP with high n, namely n≥5. Consequently their appropriate synthesis conditions and properties are not fully exploited neither their technological potential discovered. The layered structure of BLP accounts for properties anisotropy being useful for maximizing the dielectric and ferroelectric properties of BLP ceramics if a convenient orientation is selected. However such approach has been scarcely used with BLP with high n. The present study is centred on the preparation and properties of BLP with n=5. The target composition is Sr2Bi4Ti5O18 (SBTi), undoped and doped with Ca (5 molar %) prepared by conventional solid state route. The experimental conditions including uniaxial pressing pressure and heat treatment schedule for obtaining dense and single phase ceramics are reported. X-ray diffraction analysis is used to follow the crystalline phase evolution of BPL compounds as well as the dominant crystallographic orientation of BLP ceramic samples cut parallel and perpendicular to uniaxial pressing direction. It is observed that a preferential a(b) orientation is developed perpendicular to uniaxial pressing direction. The dielectric properties are measured at different frequencies and temperature on differently oriented samples. A strong dependence of the dielectric permittivity (εr) on the ceramic grain orientation is observed as it becomes twice higher if measured perpendicular to uniaxial pressing direction. Ferroelectric hysteresis loops also reflect a strong anisotropy as remanent polarization is observed to increase in a similar way. SEM microstructure observations on polished surfaces confirm different grain textures depending on the cut sample direction. Ca doping shifts Curie temperature to a higher value while decreasing εr. As a conclusion this study demonstrates that enhanced SBTi electrical properties may be accessed by a convenient choice of grain orientation and extended to higher temperature by Ca doping.
9:00 PM - F3.59
Thermodynamic Stability of Multiferroic BiFeO3. Magnetic and Dielectric Properties.
Jesus Siqueiros 1 , Carlos Ostos 1 , Alberto Sosa 2 , Nelson Almodovar 2 , X. Vendrell 3 , Maria Luisa Martinez-Sarrion 3 , Lourdes Mestres 3
1 Centro de Nanocencias y Nanotecnología, Universidad Nacional Autónoma de México, Ensenada, Baja California, Mexico, 2 Facultad de Física-IMRE, Universidad de La Habana, La Habana Cuba, 3 Facultad de Quimica, Universidad de Barcelona, Barcelona Spain
Show AbstractBiFeO3 (BFO) is a perovskite considered as multiferroic because it shows coexistence of ferroelectric (TC ≈ 1100 K) and G-type antiferromagnetic (TN ≈ 640 K) properties [1]. However, it shows a spatially modulated spin structure and a weak coupling of the order parameters at room temperature. The synthesis of this compound is not straightforward because of the formation of unwanted secondary phases of ternary oxides such as Bi25FeO39 and Bi2Fe4O9. Thermodynamic studies have shown that BFO is a metastable phase [2-3] where its stability may be understood in terms of the tolerance factor and chemical substitution, among other factors. Partial substitution of bismuth by rare-earth or alkaline-earth elements is a feasible way to stabilize the BFO phase [4]. Likewise, magnetic properties can be enhanced by a suitable ionic substitution where the result will depend strongly on the diamagnetic properties and ionic radius of the substituting ion [5]. The partial substitution of bismuth by strontium in the A-site of the perovskite structure was chosen as an alternative way to stabilize the BFO phase and to induce a net magnetic response. Bi1-xSrxFeO3 (Sr:BFO) compounds with x= 0.20, 0.25 and 0.30 were successfully obtained. The effects of calcination time (0.2 to 5 hours) and temperature (600°C to 1050°C) on the thermodynamic stability of the resulting Sr:BFO ceramics were evaluated. Rietveld refinements of XRD patterns of single-phase Sr:BFO samples with good conventional reliability factors were performed. Surface morphology of sintered samples was studied by scanning electron microscopy. The ferroelectric phase transition and dielectric loss were analyzed by impedance spectroscopy. Ferroelectric hysteresis loops (P-E) were recorded by the Sawyer-Tower method. Measurements of the field dependence of the magnetization in Bi0.75Sr0.25FeO3 showed weak ferromagnetism at room temperature. The magnetic order in a sample of this composition was corroborated by Mössbauer spectroscopy. A qualitative model developed within our group is used to explain how coupling between ferroelectric (FE) and antiferromagnetic (AFM) orders induces weak ferromagnetism. This investigation has been supported by MAT2007-63445 of CICYT, Spain; DGAPA-UNAM IN102908, IN114207 and IN109608, and CoNaCyT 82503 and 49986-F projects, Mexico.
9:00 PM - F3.6
Effect of Mechanical and Electrical Boundary Conditions on Phase Transitions in PZT Ultrathin Films.
Saad Binomran 1 , Igor Kornev 2 , Inna Ponomareva 3 , Laurent Bellaiche 4
1 Physics Department, King Saud University, Riyadh Saudi Arabia, 2 , Laboratoire SPMS, UMR 8580 du CNRS, Ecole Centrale Paris, 92295 Chatenay-Malabry France, 3 Physics Department, University of South Florida, Tampa, Florida, United States, 4 Physics Department, University of Arkansas, Fayetteville, Arkansas, United States
Show AbstractThe potential of ferroelectric thin films for many applications, such as dynamic random access memories, nonvolatile ferroelectric random access memories and integrated devices, has recently attracted a lot of research attention on these low-dimensional systems. Intense effort has been made recently to determine if (and understand how) properties of these low-dimensional systems can differ from those of the corresponding three-dimensional bulk. As a result, recent studies reveal that electrical boundary conditions and mechanical boundary conditions play a dominant role in changing the properties of ferroelectric films.In this work, first-principles-based schemes were used within the Wang-Landau algorithm to provide new insights into the phase transitions in ferroelectric ultrathin films. In particular, we investigated the character of the phase transition, as well as the associated dielectric and thermodynamic properties of PZT ultrathin films under different mechanical and electrical boundary conditions.Our results indicate that the most striking features associated with the effect of the depolarizing field on the properties of ferroelectric thin films are as follows: (i) the phase transition temperature Tc linearly decreases when decreasing the value of the screening parameter β (corresponding to an increasing of the magnitude of the depolarizing field). (ii) The maximum value of the dielectric constant (εmax) increases when decreasing the β parameter. (iii) The diffusive behavior of the phase transition is suppressed when decreasing the β parameter (i.e., when increasing the magnitude of the depolarizing field). All these three items can be understood, once realizing that the depolarizing field tends to suppress polarization and its fluctuations.Moreover, the effect of the mechanical boundary conditions on the phase transition in PZT ultrathin films was also investigated. The most three striking points that we noticed are that (i) the compressive epitaxial strain increases the ferroelectric phase transition temperature; (ii) The epitaxial strain suppresses the maximum values of the dielectric constant; (iii) The compressive strain is predicted to increase the diffuseness of the phase transition. These three items result from the fact that compressive strain fights against the depolarizing field to enhance polarization and its fluctuations, via a coupling between strain and polarization.We are confident that our results lead to a deeper understanding of phase transitions in ferroelectric thin films, in general, and will help in interpreting future experimental data, in particular.
9:00 PM - F3.60
Requirements for Ferroelectricity from A-site Size Disorder: Properties of Ba1-xCaxZrO3 Thin Films.
Hyun-Sik Kim 1 , Hans Christen 1 , David Singh 1
1 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractA-site size disorder in ABO3 perovskites has recently been proposed as a mechanism that could lead to ferroelectricity even in magnetic materials, e.g. perovskites having a B-site cation with a partially filled d-shell [D.J. Singh and C.H. Park, Phys. Rev. Lett. 100, 087601 (2008)]. Experimental verification of the limits of this mechanism is difficult in materials with a small band gap. However, highly-insulating BaZrO3 provides an ideal test case: our work shows that small Ca2+ ions (135 pm) can be substituted for the larger Ba2+ ions (160 pm) in epitaxial films, and density functional theory calculations predict a strong off-centering of the Ca2+. High-quality Ba1-xCaxZrO3 films were grown epitaxially on SrTiO3 (100) substrates using pulsed laser deposition, with the alloy remaining single-phase even at x > 0.4 and showing a nearly linear dependence of the lattice parameter on Ca concentration. The rocking curve widths (FWHM of an ω-scan through the 002 reflection) of these films were as narrow as 0.05° for x ≤ 0.28 but increasing for larger values, perhaps indicating the onset of tilt distortions. Polarization vs. field measurements show a linear P(E) dependence with no indication of ferroelectricity, and the dielectric constant (ε ≈ 50) is nearly temperature-independent. Results from Local Density Approximation (LDA) calculations explain the absence of ferroelectricity as a consequence of the strongly decreasing lattice parameter will increasing Ca concentration, but a polar behavior could be stabilized by an artificial expansion of the unit cell volume. This indicates a possible route to ferroelectricity in epitaxially-strained layers or nanocomposites. Research sponsored by the Division of Materials Science and Engineering, US Department of Energy.
9:00 PM - F3.61
Interface Magnetism in Trilayer SrTiO3/LaMnO3/La(Al0.5Sc0.5)O3 Superlattices Grown with Different Stacking Order.
Hyun-Sik Kim 1 , Michael Biegalski 2 , Jaume Gazquez 1 , Maria Varela 1 , Hans Christen 1 2
1 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractUnderstanding how the magnetization in non-magnetic or weakly-ferromagnetic systems can be enhanced by controlled epitaxial interfaces is needed to synthesize novel multiferroic composite materials. Superlattices of LaMnO3/SrTiO3 have recently been shown to exhibit enhanced magnetization resulting from interfacial effects, but macroscopic measurements cannot distinguish between the two types of interfaces present (SrO/MnO2 and LaO/TiO2). Therefore, in order to identify the role of each interface in the enhancement of the magnetization, trilayer supperlattices composed of SrTiO3/LaMnO3/La(Al0.5Sc0.5)O3 were grown on SrTiO3 (100) by pulsed laser deposition with different stacking order. The two stacking orders are denoted SLL (for SrTiO3-on-LaMnO3-on-La(Al0.5Sc0.5)O3 and LLS (La(Al0.5Sc0.5)O3-on-LaMnO3-on-SrTiO3. Note that the SLL superlattices contain the SrO/MnO2 interface while LLSs do not. The magnetization showed a strong dependence on the thickness of LaMnO3 layer (confirming its interfacial origin) and on the stacking order. In the regime of small LaMnO3 thickness (below 4 unit cells), the SLL staking order showed higher magnetism than the equivalent LLS sample. However, above the limit of ~ 4 unit cell layers, the opposite behavior is observed. This indicates that there are two mechanisms, acting at the two different interfaces, that have different relevant length scales. Z-contrast scanning transmission electron microscopy (Z-STEM) and energy electron loss spectroscopy (EELS) were used to aid in the interpretation of the macroscopic measurements. In this talk, the occurrence of two different mechanisms at the two dissimilar interfaces, with different length scales, will be proposed to understand the dependence of the enhanced magnetism in these trilayer superlattices. Research sponsored by the Division of Materials Science and Engineering (HSK, MV, and HMC) and the Division of Scientific User Facilities (MDB), US Department of Energy.
9:00 PM - F3.62
Electric Field and Strain Control of Magnetism in Multiferroic BiFeO3 Thin Films.
Mikel Holcomb 1 , A. Scholl 2 , A. Fraile-Rodriguez 3 , R. Ramesh 4
1 Physics, West Virginia University, Morgantown, West Virginia, United States, 2 , Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 3 , Swiss Light Source, Paul Scherrer Institut, Villigen PSI Switzerland, 4 , University of California, Berkeley, Berkeley, California, United States
Show AbstractIn order to understand and manipulate possible magnetoelectric coupling in multiferroics, the individual order parameters must first be fully understood. BiFeO3 (BFO), a room temperature ferroelectric and an antiferromagnet, is an excellent model system for understanding the coupling between ferroelectricity and magnetism. The ferroelectric nature of BFO was studied through a combination of in-plane and out-of-plane piezoresponse force microscopy (PFM), allowing 3D mapping of the ferroelectric polarization directions in micron-sized regions of the films. The magnetic order of BFO was obtained by using x-ray linear dichroism images using a photoelectron emission microscope (PEEM). When compared with our dichroism models, angle and temperature dependent absorption measurements allow decoupling and direction determination of the two order parameters, ferroelectric and magnetic, contributing to the photoemission signal. These studies reveal a strain-driven reduction in magnetic symmetry in thin films, leading to the formation of a preferred magnetic axis as opposed to the observed easy plane for bulk films. This reduction along with our previous proof of FE-AFM coupling allows electrical and strain control of the magnetic axis in BFO thin films. These forms of control have a strong effect on ferromagnets even at room temperature.
9:00 PM - F3.63
Octahedral Tilt Transitions in Strained PbZr1-xTixO3 Thin Films.
Daniel Tinberg 1 , Raegan Johnson 1 , Dillon Fong 2 , Timothy Fister 2 , Stephen Streiffer 2 , Yisong Han 3 , Ian Reaney 3 , Susan Trolier-McKinstry 1
1 Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania, United States, 2 Materials Science Division, Argonne National Laboratory, Argonne,, Illinois, United States, 3 Department of Engineering Materials, The University of Sheffield, Sheffield United Kingdom
Show AbstractIt has been shown for bulk materials that the transition from an untilted perovskite to a tilted perovskite can yield a significant reduction in both permittivity as well as piezoelectric coefficients. Since tilt transitions have a ferroelastic component, the strains imposed on epitaxial films are expected to change the relative stability of the tilted phases. As a model system to study this, rhombohedral compositions of PZT were investigated. Films with thicknesses greater than 350 nm were observed to have permittivities in the 400-500 range with loss tangents less than 3% at 10 kHz. At 10kHz, the films exhibited bulk Curie temperatures and bulk Curie-Weiss constants to within experimental error. At Tc the films exhibited permittivities in excess of 3000 with loss tangents less than 5%. Piezoelectric measurements were performed using the wafer flexure method and the films exhibited e31,f coefficients of -2.7 C/m^2 for PZT 80/20 films, increasing to -9.1 C/m^2 for PZT 60/40 films. X-ray diffraction was used to investigate the stability of the rhombohedral phases in the PZT phase diagram. Thick relaxed films as well as coherently (001)-oriented strained epitaxial films were investigated. The strained films exhibited Tc ~50-100°C above that seen in relaxed films. Additionally, the tilt transition temperature was shown to undergo modest increases above that in bulk. Lastly, preliminary evidence suggests that strained rhombohedral PZT with x=0.2 on (111)-oriented substrates yields films with no apparent octahedral tilt. This would suggest that the octahedral tilt transition was suppressed by at least 100°C. Ultimately, the possibility of stabilizing ferroelectric phases, which are not simultaneously tilted, may widen the range of films that have high piezoelectric coefficients at morphotropic phase boundaries.
9:00 PM - F3.64
Fabrication and Piezoelectric Properties of PbTiO3 Nanorods and Nanotubes by MOCVD.
Masaru Shimizu 1 , Ryohei Kuri 1 , Hironori Fujisawa 1 , Seiji Nakashima 1 , Yasutoshi Kotaka 2 , Koichiro Honda 2
1 , University of Hyogo, Himeji Japan, 2 , Fujitsu Lab. Ltd., Atsugi Japan
Show AbstractIn recent years, interest in the one-dimensional ferroelectrics, such as nanorods, nanowires and nanotubes has increased greatly because of their unique physical properties and potential applications. Ferroelectric nanorods, nanowires and nanotubes have been prepared using several different techniques including a hydrothermal method, a sol-gel method and a misted chemical solution deposition. In this paper, PbTiO3 nanorods and nanotubes were fabricated by MOCVD using a ZnO positive template. Their piezoelectric properties were also investigated using piezoresponse force microscopy (PFM).In the first stage of our experiments, ZnO nanorods with diameters of 140-230nm and lengths of 1-13μm as a positive template were formed on SiO2/Si at 490-550oC by MOCVD. In the next stage, PbTiO3 were deposited on ZnO template nanorods at 400-600oC by MOCVD. FE-SEM and HAADF-STEM observations revealed the uniform deposition of PbTiO3 on ZnO. No mutual diffusion between PbTiO3 and ZnO were observed by EDXA. From piezoresponse force microscopy (PFM), PbTiO3 nanorods with ZnO showed a piezoresponse of 50-100pm/V and ferroelectric domains. In the third stage, PbTiO3 nanorods covered on ZnO nanorods were mechanically scraped from the substrate and were dipped into the acid solution to etch core ZnO. Thereafter, PbTiO3 nanotubes with diameters of 100-250nm and wall thicknesses of 40-100nm were successfully obtained. PFM measurements were performed to PbTiO3 nanotubes on Pt-covered Si. Piezoresponse hysteresis loops showing ferroelectricity were observed from nanotubes. PFM measurements exhibited that PbTiO3 nanotubes showed large piezoelectric coefficients of 150-200pm/V and large strains of ~0.8% of their diameters by electric field. These strains were larger than those of PbTiO3 thin films.
9:00 PM - F3.65
Low Temperature Fabrication of Sol-Gel Derived Dielectric (Ba,Sr)TiO3 Thin Films.
Hideaki Sakurai 1 , Toshiaki Watanabe 2 1 , Nobuyuki Soyama 2
1 Central Research Institute, Mitsubishi Materials Corporation, Naka, Ibaraki, Japan, 2 Sanda Plant, Mitsubishi Materials Corporation, Sanda, Hyogo, Japan
Show AbstractWe studied the nucleation and crystallization of sol-gel derived (Ba0.7Sr0.3)TiO3 [BST(70/30)] thin films at low temperature between 500 to 600oC on Pt(111)/TiO2/SiO2/Si substrates by combination of 2-ethyl-hexanoate based solutions and modified film preparation processes. It was found that BST films could be crystallized at 500oC and that the films obtained had grainy microstructure with perovskite-single-phase and favorable electrical characteristics such as high relative permittivity (εr) of 310 at 10 kHz, and high tunability of 52% at bias electric field of 250 kV/cm. Moreover, we investigated annealing temperature dependence of BST(70/30) thin films. The results indicated εr and tunability increased with annealing temperature up to 450 and 58%, respectively.
9:00 PM - F3.8
Magnetic and Ferroelectric Properties of BiFeO3 Powders Fabricated by Hydrothermal Method.
Seung Ho Han 1 , Kyoung Sun Kim 1 , Ho Gi Kim 1 , Hyung-Won Kang 2 , Hyeung-Gyu Lee 2 , Jeong Seog Kim 3 , Chae Il Cheon 3
1 Materials Science and Engineering, KAIST, Daejeon Korea (the Republic of), 2 Electronic Materials and Device Research Center, Korea Electronics Technology Institute, Seongnam, Gyeonggi, Korea (the Republic of), 3 Semiconductor and Display Engineering, Hoseo University, Asan, Chungnam, Korea (the Republic of)
Show AbstractPerovskite BiFeO3 (BFO) is one of the few known multiferroics which shows ferroelectric, antiferromagnetic, and ferroelastic properties at room temperature. Its phase transition temperatures are high (TN=640 K, and TC=1100 K), making it very attractive not only for the fundamental physics but also from application point of view. BFO is usually fabricated by a conventional solid-state reaction at a high sintering temperature. Other fabrication methods also require high temperature heat treatment during or after the synthesis. As such, it is difficult to obtain a single phase, because the volatilization of some reactants leads to an incomplete reaction. Hydrothermal method to obtain phase pure BFO powder is worth exploring, because the synthesis of crystalline ceramic is possible by the hydrothermal reaction at a temperature of ~200 °C or lower without a further calcination step. In the case of BFO, such low processing temperatures prevent the volatilization of reactants and minimize the amount of impurities associated with calcinations and ball-milling steps.In this study, single-phase BFO powders were successively synthesized by hydrothermal method. The size and shape of BFO powders were changed by changing experimental conditions such as reaction temperature, duration time, and addition of different surfactants. The particle size and morphology were observed using scanning electron microscopy and transmission electron microscopy. Crystal structure of BFO powders was analyzed by Rietveld refinement method and Raman scattering technique at room temperature. The magnetic properties of the BFO powders were measured using VSM and SQUID. For measurement of dielectrical properties, BFO powders were pressed uniaxially into pellets and cold-isostatically pressed. The frequency-dependent dielectric constant and loss tangent were measured using an impedance analyzer, and polarization hysteresis loop was measured with an RT66A ferroelectric tester.
9:00 PM - F3.9
Microwave Synthesis of Single-crystalline Perovskite BiFeO3.
Glenda Biasotto 1 , Alexandre Simoes 2 , Maria Zaghete 1 , Jose Varela 1
1 Physical Chemistry, Unesp, Araraquara, SP, Brazil, 2 Physical Chemistry, Unifei, Itabira, MG, Brazil
Show Abstract Bismuth ferrite, one of the very few multiferroics with a simultaneous coexistence of ferroelectric and antiferromagnetic order parameters in perovskite structure, has attracted much attention for many decades since 1960. BiFeO3 (BFO) has a ferroelectric Curie temperature Tc of 850oC and an antiferromagnetic Neel temperature of 370oC [1-2]. However, potential applications of BFO in the memory devices, sensors, satellite communications, optical filters and smart devices were greatly limited due to its low insulation resistance caused by the reduction of Fe3+ species to Fe2+ and oxygen vacancies for charge compensation. A low-temperature hydrothermal synthesis route was utilized to fabricate single-phase BiFeO3 (BFO) crystallites. BFO was synthesized from an equimolar mixture of Bi(NO3)3 5H2O and Fe(NO3)39H2O in 40ml using KOH as mineralizer. The mixture was then transferred to a 125 ml Teflon reactor and placed in a microwave oven Mars-5, CEM. The microwave reaction was carried out at 160oC, 170oC and 180°C for 5 min, 30 min and 1 hour. Effects of the reaction temperature and duration time on the phase evolution, the particle size and morphologies of BFO crystallites were systematically investigated. The X-ray diffraction results indicated that perovskite BFO crystallites have been synthesized at the temperature of 180oC for 1 hour using the KOH concentration of 4M. The ferroelectric Curie temperature of our hydrothermal BFO crystallites was determined by differential thermal analysis. The hydrothermal reactions to form crystalline BFO powders were discussed based on the dissolution–crystallization process.
Symposium Organizers
Alexei Gruverman University of Nebraska-Lincoln
Craig J. Fennie Cornell University
Iwao Kunishima Toshiba Corporation
Beatriz Noheda University of Groningen
Tae Won Noh Seoul National University
F4: BiFeO3 and Other Multiferroics
Session Chairs
Craig Fennie
Ventak Gopalan
Tuesday AM, December 01, 2009
Grand Ballroom (Sheraton)
9:00 AM - **F4.1
Phase Control and Magnetoelectric Coupling in Multiferroic BiFeO3.
R. Ramesh 1
1 , University of California, Berkeley, Berkeley, California, United States
Show AbstractDepartment of Materials Science and Engineering and Department of PhysicsUniversity of California, Berkeley, CA 94720. The multiferroic BiFeO3 (BFO) system has proven to be a fertile playground for the exploration of coupled behavior, especially that between magnetism and ferroelectricity. Recent work has demonstrated the rudiments of approaches to control ferromagnetism with an electric field, using engineered heterostructures of ferromagnets coupled with BFO. The phase stability in the BFO system has also proven to be very susceptible to epitaxial constraints. In this talk, I will present to you our understanding on the interplay between heteroepitaxy and phase stability as well as the consequences of such constraints on the magnetic coupling.
9:30 AM - F4.2
Neutron Scattering Study of the Antiferromagnetic Structure of Epitaxial Multiferroic Films (BiFeO3, BiCrO3).
Hans Christen 1 , Gregory MacDougall 2 , Hyun-Sik Kim 1 , Dae Ho Kim 3 , Charlee Callender Bennett 1 , Jerel Zarestky 2 , Stephen Nagler 2
1 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Neutron Scattering Science Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 3 Department of Physics and Engineering Physics, Tulane University, New Orleans, Louisiana, United States
Show AbstractUnderstanding the antiferromagnetic spin order in multiferroic films – and how it may differ from their bulk counterparts – is important in understanding the fundamental effects of strain and other factors influencing thin films. Knowledge of a film’s spin arrangement is also required for the development of multiferroic composites in which exchange bias between a ferromagnet and an antiferromagnetic ferroelectric may be envisioned to achieve magnetic control of ferroelectricity. Such an approach is motivated by the observation that the only robust room-temperature multiferroic material (BiFeO3) is antiferromagnetic rather than ferromagnetic. BiCrO3 is an interesting but much less studied counterpart to BiFeO3, exhibiting antiferroelectricity (Tc ~ 450K) and antiferromagnetism (TN ~ 109K). For this study, we performed magnetic neutron scattering at the High Flux Isotope Reactor (HFIR) on epitaxial BiCrO3 films grown by pulsed-laser deposition. Our results indicate G-type antiferromagnetism and allow us to draw conclusions regarding the orientation of the spins with respect to the film surface. Results are compared to those obtained for BiFeO3. Research supported by the Division of Materials Science and Engineering (HMC, HSK, DHK, CJCB) and the Division of Scientific User Facilities (GJM, JLZ, SEN), U.S. Department of Energy.
9:45 AM - F4.3
Signature of Ferroelectric Dead Layer in BFO Thin Films.
A. Borisevich 1 , Hye Jung Chang 1 , S. Kalinin 2 , S. Jesse 2 , A. Morozovska 3 , M. Hujiben 4 , R. Ramesh 5 , S. Pennycook 1
1 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Center for Nanophase Materials Science, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 3 , National Academy of Sciences of Ukraine, Kiev Ukraine, 4 Science & Technology, University of Twente, Enschede Netherlands, 5 Department of Physics, University of California, Berkeley, California, United States
Show AbstractThe concept of ferroelectric “dead layer” has been extensively used for interpretation of the data on ferroelectric switching [1], equilibrium domain patterns [2], and other related properties. Possible origins of dielectric anomalies at ferroelectric interfaces were also studied theoretically [3]. To detect a spatially resolved signature of ferroelectric dead layer at the SrTiO3/(La,Sr)MnO3/BiFeO3 (STO/LSMO/BFO) interface, we used low-loss Electron Energy Loss Spectroscopy (EELS) in the aberration-corrected Scanning Transmission Electron Microscope (STEM). STEM imaging allows mapping of local ferroelectric displacements, while EELS provides spatially resolved information on elemental composition and electronic structure/dielectric properties. The images and the EELS data were acquired using a VG Microscopes HB603U operated at 300 kV equipped with a Nion® aberration corrector and a Gatan Enfina® spectrometer. The EELS compositional mapping at the interfaces was performed using principal component analysis combined with neural network interpolation. Depending on the specific energy range used for the analysis, the resulting compositional maps had a slightly different appearance. Region with low-lying core-loss edges produces a well resolved compositional map. Notably, the map for the energy range of plasmonic excitations (5 to 30 eV) shows that a region at the LSMO/BFO interface cannot be identified as any of the three phases, indicating an anomaly in dielectric properties. This feature is located on the BFO side of the interface suggesting that it is indicative of the ferroelectric dead layer. Local polarization behavior at the LSMO-BFO interfaces has also been evaluated. In an ultrathin 3.2 nm film, the polarization is approximately constant inside the film and drops off quickly at the interface. Interestingly, the first 6 layers of LSMO also show small off-center displacements of Mn, indicating induced polarization in the half-metal electrode. Atomic and electrical contributions to displacements can be deconvolved using self-consistent fitting via minimization of the free-energy functional in quazistatic approximation. Research supported by ORNL’s SHaRE Use Facility (AYB) and Center for Nanophase Materials Sciences (SVK, SJ), sponsored by the Scientific User Facilities Division; by the Division of Materials Science and Engineering (SJP), all Office of Basic Energy Sciences, U.S. Department of Energy, and by the ORNL LDRD program via a postdoctoral appointment administered jointly by ORNL and ORISE (HJC).References[1] A. K. Tagantsev, M. Landivar, E. Colla, and N. Setter, J. Appl.Phys., 78, 2623 (1995).[2] A. Kopal, P. Mokry, J. Fousek, and T. Bahnik, Ferroelectrics, 223, 127 (1999).[3] M. Stengel and N. A. Spaldin, Nature, 443, 679 (2006).
10:00 AM - F4.4
EELS Studies of Multiphase Bi-Fe-O Thin Films with Enhanced Multiferroic Behavior.
Mihaela Tanase 1 , Joon Yang 2 , Lourdes Salamanca-Riba 2
1 Physics, University of Illinois at Chicago, Chicago, Illinois, United States, 2 Materials Science and Engineering, University of Maryland, College Park, Maryland, United States
Show AbstractIn recent years multiferroic materials systems caused great interest for their possible applications in the next generation of memory and logic devices, which utilize coupling of magnetism and ferroelectricity. BiFeO3 (BFO) has received special attention because it is an intrinsic multiferroic material in the bulk that displays ferroelectricity and antiferromagnetism at room temperature. Recent studies in our lab showed that in the Bi-Fe-O system grown by PLD (Pulsed Laser Deposition) on SrTiO3 substrates there are several coexisting phases of different structure, composition, and electrical and magnetic properties. The microstructural evolution of the BiFeO3 , α-Fe2O3 and γ-Fe2O3 multiphase material is controlled by the oxygen partial pressure during growth and affects the relaxation of the misfit strain as well as the magnetic and ferroelectric properties of the BFO films. The enhanced piezoelectric character of the BFO/Fe2O3 interface observed in our previous work is correlated with a variation of Fe2+/Fe3+ across the interface, and with the variation in the Bi and O stoichiometry from the bulk of the BFO grains to the Fe2O3 interfaces, measured using EELS (Electron Energy Loss Spectroscopy) in STEM mode. The lattice distortions across the multiphase interface also plays a role in the enhancement of the ferroelectric behavior.This research is supported by the National Science Foundation under the University of Maryland MRSEC DMR 0520471.
10:15 AM - F4.5
Opto-transport Measurements at Domain Walls in Multiferroic BiFeO3.
Jan Seidel 1 2 , Seung-Yeul Yang 3 , Steven Byrnes 1 2 , Padraic Shafer 3 , Chan-Ho Yang 1 , Joel Ager III 2 , Lane Martin 2 , Gustau Catalan 4 , James Scott 4 , Ramamoorthy Ramesh 1 2 3
1 Department of Physics, UC Berkeley, Berkeley, California, United States, 2 Materials Sciences Division, Lawrence Berkeley National Lab, Berkeley, California, United States, 3 Department of Materials Sciences and Engineering, UC Berkeley, Berkeley, California, United States, 4 Department of Earth Sciences, University of Cambridge, Cambridge United Kingdom
Show AbstractWe present scanning probe based opto-transport measurements in the complex oxide material BiFeO3 under visible light illumination. We observe an anomalous photovoltaic effect arising from a previously unknown mechanism, namely structurally driven steps of the electrostatic potential that occur at ferroelectric domain walls. These potential steps - and, in turn, the photovoltaic effect - can be fully controlled through the domain structure in these films, e.g. by local switching using electric fields. This domain wall driven effect offers a new route to optimization and application of photovoltaic devices.
11:00 AM - F4.6
Multiferroicity in Manganites from First Principles.
Jun Hee Lee 1 , Karin Rabe 1
1 Physics and Astronomy, Rutgers University, Piscataway, New Jersey, United States
Show AbstractOne emerging strategy in the theoretical design of new multiferroic materials is the identification of systems where ferromagnetic spin alignment decreases the frequency of the lowest ir-active polar phonon [1]. It was recently reported that ferromagnetic spin alignment typically shifts the lowest polar phonon frequency in B-cation magnetic perovskites with a d3 electron configuration, but not in those with d5 electron occupation [2]. In this talk, we present a survey of the phonon dispersions of the ideal cubic perovskite phase of a selected set of perovskite oxides, computed from first principles. We find a very large destabilization of the lowest frequency polar phonon in CaMnO3 and SrMnO3, both with d3 cations. We analyze the theoretical phase diagram of SrMnO3 for epitaxial strain, showing that a transition to a ferromagnetic-ferroelectric state is favored as strain increases. This state has polarization comparable to BaTiO3 and a predicted Curie temperature above 100K. From analysis of this example, we develop and discuss guidelines for identifying additional promising candidates for systems with multiferroic states based on the spin-phonon-coupling mechanism. [1] C. J. Fennie and K. M. Rabe, Phys. Rev. Lett. 97, 267602 (2006) [2] N. Ray and U. V. Waghmare, Phys. Rev. B 77, 134112 (2008)
11:15 AM - F4.7
Strain-Induced Ferromagnetism and Ferroelectricity in EuTiO3 Grown by Molecular-Beam Epitaxy.
June Hyuk Lee 1 2 , Lei Fang 3 , Xianglin Ke 4 , Eftihia Vlahos 2 , Youngwoo Jung 3 , Lena Fitting Kourkoutis 5 , Philip Ryan 6 , John Freeland 7 , Tassilo Heeg 1 , Martin Roeckerath 8 , M. Bernhagen 9 , Reinhard Uecker 9 , Chris Hammel 3 , Jurgen Schubert 8 , David Muller 5 , Craig Fennie 5 , Venkatraman Gopalan 2 , Peter Schiffer 4 , Ezekiel Johnston-Halperin 3 , Darrell Schlom 1
1 Department of Materials Science and Engineering, Cornell University, Ithaca, New York, United States, 2 Department of Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania, United States, 3 Department of Physics, Ohio State University, Columbus, Ohio, United States, 4 Department of Physics, Pennsylvania State University, University Park, Pennsylvania, United States, 5 School of Applied and Engineering Physics, Cornell University, Ithaca, New York, United States, 6 , Ames Laboratory, Ames, Iowa, United States, 7 Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois, United States, 8 Institute of Bio- and Nano-Systems, IBN-1, Julich GmbH and Julich-Aachen Research Alliance, Julich Germany, 9 , Institute for Crystal Growth, Berlin Germany
Show AbstractRecently biaxial strain has been predicted to induce a multiferroic ground state in EuTiO3 and change its normally paraelectric and antiferromagnetic ground state into a state that is simultaneously ferromagnetic and ferroelectric [C.J. Fennie and K.M. Rabe, Phys. Rev. Lett. 97, 267602 (2006)]. This multiferroic state is predicted to be a strong ferromagnet (spontaneous magnetization ~7 µB/Eu) at the same time that it is a strong ferroelectric (spontaneous polarization ~10 µC/cm2). To assess these predictions that would establish EuTiO3 as the world’s strongest ferromagnetic ferroelectric, we have grown epitaxial EuTiO3 thin films on (001) SrTiO3 and (110) DyScO3 substrates by reactive molecular-beam epitaxy (MBE). EuTiO3/SrTiO3 is unstrained and EuTiO3/DyScO3 is strained in biaxial tension sufficiently that according to theory it should be in the desired multiferroic state. Europium and titanium were codeposited onto the substrates under an oxygen background partial pressure of 3×10-8 Torr at a substrate temperature of 650 °C. X-ray diffraction (XRD) revealed phase-pure, epitaxial (001)-oriented EuTiO3 thin films commensurately strained to the substrates they were grown on. The rocking curve full width at half maximum values were as narrow as 22 arc sec (0.006°). Scanning transmission electron microscopy (STEM) revealed epitaxial films with abrupt interfaces between film and substrate. Rutherford backscattering spectrometry (RBS) confirmed that the films were stoichiometric. X-ray absorption spectroscopy (XAS) and electron energy loss spectroscopy (EELS) confirmed the desired Eu2+ and Ti4+ oxidation state of the EuTiO3 films. Magneto-optic Kerr effect (MOKE) and SQUID measurements revealed that the unstrained EuTiO3 was antiferromagnetic with TN = 5.5 K in agreement with bulk unstrained EuTiO3, whereas the strained EuTiO3/DyScO3 was ferromagnetic with TC = 4.6 K. Optical second harmonic generation (SHG) revealed that the unstrained EuTiO3/SrTiO3 was not polar, as expected, but that the strained EuTiO3/DyScO3 went through a phase transition at about 225 K to polar point group mm2 in agreement with theory and in this state domain switching by electric fields was observed. Our results thus establish that strain induces a strong multiferroic state in EuTiO3 in agreement with predictions.
11:30 AM - F4.8
Strain-symmetry Induced Ferroelectricity with Weak Ferromagnetic Moments in Epitaxial BiCrO3Films.
Dae Ho Kim 1 3 , Michael Biegalski 2 , Hans Christen 3
1 Department of Physics and Engineering Physics, Tulane University, New Orleans, Louisiana, United States, 3 Materials Science and Technology Division, Oak Ridge Natioanl Laboratory, Oak Ridge, Tennessee, United States, 2 Center for Nanophase Materials Science, Oak Ridge Natioanl Laboratory, Oak Ridge, Tennessee, United States
Show AbstractThe symmetry of strain exerted on epitaxial films by crystalline substrates plays an important role in manipulating ferroelectric properties. It is often just as significant as the well-studied effect of the magnitude of strain resulting from lattice mismatch between the film and substrate. In multiferroics, where ferroicity (or antiferroicity) both in magnetism and polarization occur simultaneously, the importance of strain-symmetry becomes more significant. Here we investigate the multiferroic properties of epitaxial films of BiCrO3 under structural modifications by epitaxial strain. In contrast to structurally similar BiFeO3 with large polarization and antiferromagnetic properties, BiCrO3 exhibits antiferroelectricity and a weak ferromagnetic moment parasitic to its antiferromagnetic order when grown on (001) oriented SrTiO3 substrates. Surprisingly, we find that a small but significant modification of the structure resulting from the change in strain-symmetry stabilizes a strong remnant ferroelectric polarization in BiCrO3 films grown on (111) oriented SrTiO3 substrates. Moreover, the strain driven ferroelectricity is accompanied by a distinctive two-step switching behavior. The magnetic properties of BiCrO3 were not significantly affected by this transition. The antiferroelectric-to-ferroelectric phase transition driven by strain-symmetry modification provides very instructive insights into the multiferroic properties of bismuth-based perovskites. Research sponsored by the Division of Materials Sciences and Engineering (DHK, HMC) and the Division of Scientific User Facilities (MDB), Office of Basic Energy Sciences, U.S. Department of Energy.
11:45 AM - F4.9
Nanolamellar BaTiO3-CoFe2O4 Magnetoelectric Bi-Crystal.
Shenqiang Ren 1 , Mark Laver 2 , Manfred Wuttig 1
1 Materials and Science Engineering Department, University of Maryland at College Park, College park, Maryland, United States, 2 , NIST Center for Neutron Research, Gaithersburg, Maryland, United States
Show AbstractWe report for the first time on a spontaneously formed nanolamellar spinel-perovskite BaTiO3-CoFe2O4 bi-crystal. The crystal was synthesized by a long time (24hrs) anneal at 1473 K of a sol-gel produced powder. A (1-10) interface joins the two lattices that have a common [111] direction. Epitaxy is achieved by interlacing the two structures over the extent of one oxygen octahedron. The superlattice is magnetoelectric with a frequency dependent coupling coefficient of maximally 20mV/Oecm which is the largest currently known value for room temperature natural MEs. The BaTiO3 component is a ferroelectric relaxor with a Vogel-Fulcher temperature of 311 K. Since the material can be produced by standard ceramic processing methods, the discovery represents great potential for magnetoelectric devices.
12:00 PM - F4.10
Structural Control and Exchange Bias in Fe3O4/BiFeO3 Vertical Nanocomposites.
Emily Weal 1 , Mary Vickers 1 , Zhenxing Bi 2 , Haiyan Wang 2 , Judith MacManus Driscoll 1
1 Department of Materials Science and Metallurgy, University of Cambridge, Cambridge United Kingdom, 2 Department of Electrical and Computer Engineering, Texas A&M University, College Station, Texas, United States
Show AbstractWe have produced Fe3O4/BiFeO3 vertical nanocomposite films, achieving careful control of both the constituent phases and the microstructure of the composite. An epitaxial relationship between Fe3O4 columns and the STO substrate has been obtained, despite large (~7%) epitaxial strains. This has not been seen before in films of thickness greater than ~30 nm. Magnetic measurements show that a film consisting of 10% Fe3O4 vertical columns in a BiFeO3 matrix demonstrates exchange bias. Not only is this the first demonstration of exchange bias in vertical composites, but it has also been achieved in films significantly thicker than those displaying the effect using bi-layer structures.
12:15 PM - F4.11
Control of Magnetic and Dielectric Properties by Epitaxial Strain in Orthorhombic TbMnO3 and YMnO3.
Xavier Marti 1 , Ignasi Fina 1 , Vassil Skumryev 2 3 , Florencio Sanchez 1 , Lourdes Fabrega 1 , Josep Fontcuberta 1
1 Materials Magnètics, Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Bellaterra, Barcelona, Spain, 2 Departament de Física, Universitat Autonoma de Barcelona, Bellaterra, Barcelona, Spain, 3 , Institut de Recerca i Estudis Avançats, Barcelona, Barcelona, Spain
Show AbstractDespite all orthorhombic rare earth manganites are antiferromagnetic, the magnetic structure depends on the unit cell topology (angles and distances). Maybe one of the major recent findings is that ferroelectricity is expected either because the spins order non-colinearly (Gd – Dy) or via small atomic displacements due to exchange striction (Ho – Lu). It follows that functional properties and unit cell distortion are intimately related. Control of the epitaxial strain in thin film growth provides a new way to modify the topology and, thus, tune the magnetic and dielectric properties.We first present how the unit cell distortion can be tailored in epitaxial YMnO3 and TbMnO3 thin films by changing the deposition conditions or partial substituition of Mn by Co. In a second step, we show that although antiferromagnetic behaviour is observed for the fully relaxed thin films, an increasing ferromagnetic behaviour appears as the unit cell is more distorted. We discuss on the magnetic anisotropy measurements that support that spins are canted away from the [010] direction. As we mentioned, the modification of the magnetic structure is expected to resound in the dielectric properties: we present the temperature dependence of the electrical permittivity reproducing the anomalies early observed in bulk at TN and, moreover, showing a concomitant change of their behaviour (amplitude and location) with the unit cell distortion.
F5: Dynamic Switching Behavior
Session Chairs
Alexei Gruverman
Andrew Rappe
Tuesday PM, December 01, 2009
Grand Ballroom (Sheraton)
2:30 PM - **F5.1
Deciphering and Controlling the Mechanisms of Polarization Switching on a Single Defect Level.
Sergei Kalinin 1 , Peter Maksymovych 1 , Stephen Jesse 1 , Art Baddorf 1 , Nina Balke 1 , Oleg Ovchinnikov 1
1 , ORNL, Oak Ridge, Tennessee, United States
Show AbstractThe mechanisms of the polarization switching in ferroelectric and multiferroic materials are controlled by the atomistic and mesoscopic defects that act as nucleation centers for new phases and pinning sites for moving transformation fronts. In materials with several thermodynamically equivalent states the defects can also select the transformation pathways and determine the final state of the system. The atomic and electronic structures of defects have become accessible with the advances in electron microscopy; however, the dynamic mechanisms of phase transitions on a single defect level until recently remained an enigma.Here, I present the results of recent studies of polarization switching in ferroelectrics using Switching Spectroscopy Piezoresponse Force Microscopy. Following the demonstration of imaging capability [1] and single defect resolution [2], SS-PFM was used to study polarization switching behavior on a number of well-defined systems, including (a) 24° grain boundary in (100) rhombohedral ferroelectric, (b) 180° domain wall in uniaxial ferroelectric, and (c) ferroelastic 71° wall in (100) rhombohedral ferroelectric. The synergy between SS-PFM imaging and mesoscopic theory allows deterministic polarization reversal mechanisms to be determined on a single-defect level.Recently, the electromechanical detection was integrated with the current and resonance frequency measurements in the ultra-high vacuum environments, enabling (a) implementation of polarization-controlled tunneling [3] and (b) probing voltage-dependence of mechanical contact behavior. These potential applications of these methods for probing local bias-induced transitions in antiferroelectric materials and electrochemical reactions are discussed. 1.S. Jesse, B.J. Rodriguez, A.P. Baddorf, I. Vrejoiu, D. Hesse, M. Alexe, E.A. Eliseev, A.N. Morozovska, and S.V. Kalinin, Direct imaging of Spatial and Energy distribution of Nucleation Centers in Ferroelectric Materials, Nature Materials 7, 209 (2008).2.S.V. Kalinin, S. Jesse, B.J. Rodriguez, Y.H. Chu, R. Ramesh, E.A. Eliseev and A.N. Morozovska, Probing the role of single defects on the thermodynamics of electric-field induced phase transitions, Phys. Rev. Lett. 100, 155703 (2008).3.P. Maksymovych, S. Jesse, P. Yu, R. Ramesh, A.P. Baddorf, and S.V. Kalinin, Polarization Control of Electron Tunneling into Ferroelectric Surfaces, Science 324, 1421 (2009).
3:00 PM - F5.2
Visualization of Intriguing Polarization Switching Behaviors in Multiferroic BiFeO3 Thin Films.
Tae Won Noh 1 , Tae Heon Kim 1 , Sang Mo Yang 1 , Seung Yup Jang 1 , Daniel Ortiz 2 , Chang Bum Eom 2 , Tae Kwon Song 3 , Jin-Seok Chung 4 , Jong-Gul Yoon 5
1 ReCOE & FPRD, Department of Physics and Astronomy, Seoul National University, Seoul Korea (the Republic of), 2 Department of Materials Science and Engineering, University of Wisconsin, Madison, Wisconsin, United States, 3 School of Nano and Advanced Materials Engineering, Changwon National University, Changwon, Gyengnam, Korea (the Republic of), 4 Department of Physics and CAMDRC, Soongsil University, Seoul Korea (the Republic of), 5 Department of Physics, University of Suwon, Suwon, Kyunggi-do, Korea (the Republic of)
Show AbstractBiFeO3 (BFO) is one of remarkable multiferroic materials. It has a very high ferroelectric Curie temperature (TC) of ~1,100 K and an antiferromagentic Neel temperature (TN) of ~640 K. Its ferroelectric polarization is comparable to that of Pb(Zr,Ti)O3. Therefore, understandings on its polarization switching phenomena could be quite interesting scientifically as well as technologically. Recently, we developed a new piezoelectric force microscopy (PFM) method to obtain time-dependent global switching behavior of nanoscale domains in ferroelectric films [1]. In this presentation, we will present our efforts to visualize intriguing polarization switching behaviors in multiferroic BFO thin films using our modified PFM configuration. In our studies, we used two kinds of high-quality Pt/BFO(200 nm)/SrRuO3(100 nm) heterostructures which were epitaxially grown on 2° miscut SrTiO3(001) and (111) substrates [2]. In BFO(001) films, we found that ferroelectric domains grow along a particular direction, which is quite different from the isotropic domain growth observed in most other ferroelectric thin films. The directionality depends on the electrical polarity of applied switching pulse. While the domain grows along the downhill miscut direction under a negative bias, the domain growth direction becomes reversed under a positive bias. By applying both positive and negative pulses, we also found that the domain wall movements have some memory effects. We elucidated that such a directional domain growth should come from the strain gradient of BFO layer on terraces, which leads to a difference between the nucleation energy barriers at each unit cell. This unique domain switching behavior can be applied in a new type of memory device with the high performance and the high speed. In BFO(111) films, we observed that domain growth pattern changes from a circular-like growth to a dendritic stripe growth with an increasing negative bias. Such a change in domain growth behavior might be originated from a competition between nucleation process and domain wall motion. The domain growth under a low negative bias is dominantly governed by domain wall motion due to high nucleation-energy-barriers, resulting in a circular-like domain pattern. Under a high bias, more domain nucleation can occur, leading to a more complicated and ragged domain pattern. In addition, we found that domain growth behavior does not change for the positive bias. We believe that such a switching polarity dependence of domain dynamics might be caused by a different density of structural defects at top/bottom interface. Further experimental evidences will be discussed during the presentation.[1] D. J. Kim et al., Appl. Phys. Lett. 91, 132903 (2007)[2] R. R. Das et al., Appl. Phys. Lett. 88, 242904 (2006)
3:15 PM - F5.3
Deterministic Control of Polarization Switching in Multiferroic Materials.
Nina Balke 1 , Samrat Choudhury 2 , Lane Martin 3 , Ying-Hao Chu 4 , Mark Huijben 5 , Stephen Jesse 1 , Long-Qing Chen 2 , Ramamoorthy Ramesh 3 , Sergei Kalinin 1
1 CNMS, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 , Pennsylvania State University, University Park, Pennsylvania, United States, 3 , University of California, Berkeley, California, United States, 4 , National Chiao Tung University, Hsin Chu Taiwan, 5 , University of Twente, Enschede Netherlands
Show AbstractIn multiferroic materials, strain and magnetization states can be altered by ferroelectric switching due to order parameter coupling which opens the door to new concepts for information storage. However, realization of the next generation of magnetoelectric, strain-coupled, and domain-wall based devices necessitates the deterministic control of polarization switching in multiaxial multiferroics. In rhombohedral ferroelectrics, application of electric field in the pseudocubic (001) direction can lead to 180 degree ferroelectric switching and 71 degree and 109 degree ferroelastic switching. Depending on the switching process, the properties of the final domain structures are remarkably different. In the case of the conductive domain wall in rhombohedral BiFeO3 thin films, for example, only the 109 degree and 180 degree domain walls show increased conductivity whereas 71 degree domain walls do not show this effect. Other examples for BiFeO3 are the dependence of the exchange bias on the total lenghts of 109 degree domain walls in the as-grown domain structure and the change of the magnetic domain structure for non-180 degree ferroelectric switching. This shows that we need to know how to control the switching process in BiFeO3 in order to utilize the order parameter coupling and domain wall functionality for future devices. Here we demonstrate the control the ferroelectric domain switching in BiFeO3 thin films on differently oriented substrates by breaking the symmetry of the electric field around a biased scanning probe microscopy probe by moving the tip along defined diretions during the poling process. This method enables us to direct the ferroelectric switching process which offers a reliable pathway for magnetoelectric, domain-wall based and strain coupled devices. The fabrication of predefined domain patterns which include all possible polarization orientations and the creation of arbitrary domain walls without using high voltages in BiFeO3 are shown. The possibility to create arbitrary domain patterns is crucial to investigate the role of local strain or polarization states in the macroscopic material behavior. The control of ferroelectric switching can also be utilized to create closure domain pattern which are believed to served as preform for vortex domains which is a strongly discussed topic in the field of ferroelectrics. Phase-field modeling is used to explain the control of ferroelectric switching.
3:30 PM - F5: Dynamics
Break
3:45 PM - **F5.4
Local and Global Probes of Nonlinearity in Ferroelectric Thin Films.
Susan Trolier-McKinstry 1 , Patamas Bintachitt 1 , Ichiro Fujii 1 , Stephen Jesse 2 , Katyayani Seal 2 , Sergei Kalinin 2
1 Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania, United States, 2 Center for Nanoscale Materials Science, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractPolycrystalline PbZr0.52Ti0.48O3 films are of increasing interest in low voltage actuators for piezoelectric microelectromechanical systems. In this work, Rayleigh and Preisach approaches were used to describe the large field dielectric response measured on macroscopic electrodes (e.g. with dimensions in the mm range). The results were then compared with local measurements made using piezoforce microscopy. In SSPFM measurements on top electrodes it was found that the switching was coupled across grain boundaries on lateral length scales on the order of 1 – 2 microns, based on the patchiness of the nucleation bias maps. This suggests that hundreds to thousands of grains interact during a switching process. Reasonable agreement between the switching processes measured on local and global scales was obtained. At lower excitation levels, Band Excitation Piezoelectric Force Microscopy (BE-PFM) enabled quantitative measurements of the local piezoelectric nonlinearity. 4 μm thick films were nearly uniform in their Rayleigh coefficient, suggesting that any heterogeneities in the response developed at lateral length scales below the resolution of the PFM measurement. In contrast, thinner films showed significantly more patchiness in their response, so that fluctuations in behavior developed at a lateral length scale on the order of 0.6 to 2.5 micron. These variations did not appear to be correlated directly with the surface topology.
4:15 PM - F5.5
Direct Nanoscale and Nanosecond Investigation of the Mechanical and Ferroelectric Influence of Individual Domain Defects on Polarization Switching.
Nicholas Polomoff 1 , Sungjun Lee 1 , Ying-Hao Chu 2 , Pu Yu 3 , Ramamoorthy Ramesh 3 , Bryan Huey 1
1 Institute of Material Science, University of Connecticut, Storrs, Connecticut, United States, 2 , National Chiao Tung University, Hsin Chu Taiwan, 3 Dept. of Physics, University of California Berkeley, Berkeley, California, United States
Show AbstractIt has recently been demonstrated that ferroelectric domain switching dynamics can be directly monitored with combined nanosecond and nanoscale resolution through High Speed Piezo Force Microscopy (HSPFM). Generally, domain nucleation rates increase exponentially with the applied bias, as due growth rates, though the activation energies for each mechanism are distinctly different and highly location dependent. Leveraging recently achieved temporal resolution of just 10 nanoseconds, this investigation of the nascent stages of domain nucleation and growth also consistently reveal a higher initial growth rate during the first 100 to 500 nanoseconds of poling. This observation, reported here for the first time, is proposed to directly reveal the lowered activation energy of specific sample defects. The spatial influence of these defects extends to a size of 50 to 100 nanometers, after which the activation energy to switch polarity at the expanding domain periphery increases (slowing the growth rate itself) as it becomes essentially independent of the initial nucleation site. Accordingly, the initial and ultimate domain growth rates are quantitatively compared and mapped, as is the statistical weighting of the calculated defect (initial), and film (final), activation energies. These HSPFM results are finally correlated, and agree with, local changes in the mechanical compliance of the sample through Atomic Force Acoustic Microscopy (AFAM), revealing diminished sample stiffness at nucleation site cores. Such investigations are crucial for accurate modeling of ultimate area switching rates in ferroelectric devices as well as optimal sample processing for device performance.
4:30 PM - F5.6
Why Vinylidene Fluoride is a Special Ferroelectric Material.
Stephen Ducharme 1
1 Physics and Astronomy, University of Nebraska, Lincoln, Nebraska, United States
Show AbstractPolyvinylidene fluoride (PVDF, -CH2-CF2) stands out among macromolecular ferroelectric materials because of its large fixed dipole moment, compact structure, and the essential link be-tween intramolecular vibrations and soft phonons. Copolymerization with trifluoroethylene or tetrafluoroethylene enriches the phase diagram where the main effects are slight reduction in spontaneous polarization and the ferroelectric-paraelectric phase transition temperature. Vinylidene fluoride oligomers also readily form ferroelectric crystals. Nearly any other variation in molecular structure adversely affects chemical stability, crystallinity, or rotational mobility. For example, simple substitution of slightly larger chlorine for fluorine completely destabilizes the ideal all-trans molecular structure that constitutes the ferroelectric phase because of increased intramolecular steric hindrance. Substitution of the comparably slim CN for fluorine, on the other hand, retains the all-trans structure, and also the ferroelectric state, but makes polarization switching much more difficult due to intermolecular steric hindrance. Furthermore, changing the backbone bonding of PVDF immediately disrupts the hexagonal dihedral symmetry essential to polarization switching, and to the existence of the phase ferroelectric-paraelectric phase transi-tion. This presentation will review these and other reasons why vinylidene fluoride is special in-deed. This work was supported by the National Science Foundation (ECS-0600130), the Depart-ment of Energy (DE-FG02-08ER46498), and the Nebraska Research Initiative.
4:45 PM - F5.7
In Situ Transmission Electron Microscope Observation of Domain Behavior in Multiferroic Structures Under Applied DC Bias.
Christopher Winkler 1 , Lane Martin 2 , Craig Johnson 1 , Mitra Taheri 1
1 Materials Science & Engineering, Drexel University, Philadelphia, Pennsylvania, United States, 2 Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractSelect multiferroic materials exhibit a coupling between ferroelectric and magnetic order parameters, mediated by a quantum-mechanical exchange interaction. One of the most widely studied magneto-electric multiferroics is the perovskite BiFeO3 (BFO). The magneto-electric coupling in BFO allows for control of the ferroelectric domain structures via applied electric fields. Recent advances in synthesis techniques have enabled the growth of high quality, epitaxial thin films. Because of these unique properties, BFO and other magneto-electric multiferroics constitute a promising class of materials for incorporation into devices such as high density ferroelectric and magnetoresistive memories, spin valves, and magnetic field sensors. Before BFO can be integrated into devices, however, a full understanding of its ferroelectric and antiferromagnetic domain behavior across a range of time and length scales needs to be developed. Improved control of ferroelectric domain structures is critical for increasing the performance of ferroelectric and magnetoresistive memories, because memory switching speed and capacity are limited by domain wall mobility and domain size, respectively.We investigated the ferroelectric domains in BFO using diffraction contrast transmission electron microscopy (TEM) and high-resolution electron microscopy (HREM). Diffraction contrast was used to distinguish adjacent domains with different polarization directions, and HREM images were analyzed to determine the atomic structure of domain walls. We present in situ TEM experiments designed to probe the response of BFO thin films to an applied DC bias, thereby enabling control of ferroelectric switching in the BFO thin film. Domain wall movement will be captured using digital streaming video at 30Hz, at both low and high magnifications. We discuss the effect of dislocation sites on domain formation and propagation. Correlating the results of the biasing experiments with domain morphology will lead to improvements in quantitative models that describe and predict domain kinetics across a range of length scales from micrometers to nanometers.
5:00 PM - F5.8
Nonlinear Dynamics of Domain Walls in Epitaxial Ferroelectric Thin Film.
Sang Mo Yang 1 , Ji Young Jo 1 , Tae Heon Kim 1 , Tae Kwon Song 2 , Jong-Gul Yoon 3 , Ho Nyung Lee 4 , Seungyoung Park 5 , Younghun Jo 5 , Tae Won Noh 1
1 ReCOE & FPRD, Department of Physics & Astronomy, Seoul National University, Seoul Korea (the Republic of), 2 School of Nano and Advanced Materials Engineering, Changwon National University, Changwon, Gyeongnam Korea (the Republic of), 3 Department of Physics, University of Suwon, Suwon, Gyeonggi-do Korea (the Republic of), 4 Materials Science and Technology Division, Oak Ridge National Lab., Oak Ridge, Tennessee, United States, 5 Quantum Materials Research Team, Korea Basic Science Institute, Daejeon Korea (the Republic of)
Show AbstractFerroelectric (FE) materials have been one of the most interesting matters for last decades, due to scientific issues as well as application potentials such as non-volatile memory devices. For this reason, there have been developed many experimental methods to determine properties of the FE materials. Among them, we have been widely and easily used the measurements of switching current and hysteresis loop. However, there are little experimental works on the microscopic studies such as domain wall dynamics using them. Here, we report our recent stuides on the nonlinear dynamics of domain walls in Pb(Zr,Ti)O3 (PZT) thin films using switching current measurements and hysteresis loops.The sample studied was a high-quality epitaxial PZT thin film grown on SrRuO3/SrTiO3 (001) substrates using pulsed laser deposition [1]. We demonstrated FE domain wall velocity v has nonlinear response, which is classified with creep, depinning, and flow regimes in dependence with strength of external electric field E [2]. First, we obtained reliable values of v for various E at room temperature T using our modifed piezoresponse force microscopy (PFM) [3]. Second, to widen the accessible region of T and E, we used switching current measurements to obtain the data of v using the relation of v ~ 1/t0, where t0 is a characteristic switching time in the Kolmogorov-Avrami-Ishibashi model [4]. We revealed experimentally the v-E relation, which follows the predictions of the statistical physics on interface growth. We also obtained values of two critical exponents, μ ~ 1.0 and θ ~ 0.7, from the data in creep and the depinning regimes, respectively. Here, μ and θ are dynamic exponent relataed to disorder class and velocity exponent implied fractal dimension of domains, respectively.Furthermore, using well-define hysteresis loops, we revealed experimentally the dynamic phase diagram for FE domain walls driven by ac field [5]. We observed two regimes behavior for frequency f-dependence of coercive field EC, i.e., the slopes for log f vs. log EC changed. We found that this phenomena indicated dynamic phase transition between creep regime to flow regime. From this fact, we could obtain values of dyanmic crossover and confirm the reliabilty of the data through the fitting by threoritical formula. This work provides us new insights on relation between microscopic switching dynamics of domains and macroscopic hysteresis loops in ferroic materials.[1]H. N. Lee et al., Phys. Rev. Lett. 98, 217602 (2007).[2]J. Y. Jo et. al., Phys. Rev. Lett. 102, 045701 (2009).[3]S. M. Yang et al., Appl. Phys. Lett. 92, 252901 (2008).[4]Y. Ishibashi et al., J. Phys. Soc. Jpn. 31, 506 (1971).[5]T. Nattermann et al., Phys. Rev. Lett. 87, 197005 (2001)
5:15 PM - F5.9
Route to a Magnetoelectic Device with In-plane Electrodes.
Chad Folkman 1 , Seung-Hyub Baek 1 , Ho-Won Jang 1 , Chang-Beom Eom 1 , Jingxian Zhang 2 , Long-Qing Chen 2 , Chris Nelson 3 , Xiaoqing Pan 3
1 Material Science and Engineering, University of Wisconsin - Madison, Madison, Wisconsin, United States, 2 Material Science and Engineering, Pennsylvania State University, University Park, Pennsylvania, United States, 3 Material Science and Engineering, University of Michigan - Ann Arbor, Ann Arbor, Michigan, United States
Show AbstractThe pursuit of a room temperature device exploiting the intrinsic electronic and magnetic ordering of BiFeO3 has accentuated the importance of identifying ferroelectric domain switching paths with an applied electric field (E). A recent demonstration of coupled ferroelectricty and antiferromagnetic exchange bias utilized an in-plane electric field applied with a planar electrode to promote a desired switching path.1 However, no polarization versus electric field (P – E) was reported; consequently, the study lacked information like the amount of leakage current through the sample. This motivated us to investigate the in-plane switching characteristics using a planar electrode patterned on high crystalline quality epitaxial BiFeO3 thin films deposited by RF magnetron sputtering. In-plane P – E measurements were made both parallel and perpendicular to a preexisting (as-deposited) stripe ferroelectric domain pattern. A large non-linearity and a high remnant polarization were observed with the electric field applied perpendicular to the striped domain pattern consistent with strong ferroelectric behavior (i.e. irreversible). However, an electric field applied parallel to the striped domain walls resulted in weak ferroelectric behavior observed from a low remnant polarization and a more linear response (i.e. reversible). Thermodynamic phase field simulations were used to explain the observations in the context of domain wall motion and polarization rotation. Therefore, the as-grown domain wall configurations are vital and must be engineered to particular applications. Applications range from the novel magnetoelectric devices to more established technologies like piezoactuators and ferroelectric random access memories. 1. Chu, Y. H. et al. Electric-field control of local ferromagnetism using a magnetoelectric multiferroic. Nature Materials 7, 478-482 (2008).
5:30 PM - F5.10
Nanoscale Polarization Switching Dynamics Near 180 Degree Domain Walls in Ferroelectrics.
Vasudeva Rao Aravind 1 , Samrat Choudhury 2 , Yulan Li 1 , Katyayani Seal 3 , Stephen Jesse 3 , Anna Morozovska 4 , Eugene Eliseev 5 , Long-Qing Chen 1 , Venkatraman Gopalan 1 , Sergei Kalinin 3
1 Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania, United States, 2 , University of Wisconsin, Madison, Wisconsin, United States, 3 Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 4 Institute of Semiconductor Physics, National Academy of Sciences of Ukraine, Kiev Ukraine, 5 Institute for Problems of Materials Science, National Academy of Sciences of Ukraine, Kiev Ukraine
Show AbstractApplications of ferroelectric materials in data storage, piezoelectric and FeRAM require understanding of domain wall motion mechnisms. Domain wall motion in ferroelectric materials is strongly affected by lattice, surface and defect pinning effects. A variant of Piezoresponse Force Microscopy (PFM) called Switching Spectroscopy PFM (SSPFM) is ideally suited to probe the local domain switching near ferroelectric domain walls and study domain dynamics and polarization switching on the nanoscale. Application of a dc field to a conductive tip results in local polarization reversal, while subsequent imaging allows visualization of the switched domain. Using localized electric field of a scanning probe microscopy tip, we discover a surprisingly rich range of dynamic polarization behaviors in the vicinity of the initially flat 180 degree ferroelectric domain wall in lithium niobate. In the vicinity of the biased probe tip, the domain wall bends, attracts or repels from the probe apex, depending on the sign and value of the applied bias. The wall profoundly affects switching on length scales of the order of micrometers. Systematic SSPFM experiments with varying bias voltages are used to plot an experimental phase diagram summarizing the effect of bias voltage on nucleation in the vicinity of a 180 degree domain wall. These experimental results are compared with first principles theory to calculate the energy required for the propagation of a ferroelectric domain wall overcoming the atomistic peierl’s energy barrier. Finally the hystresis loops obtained in lithium niobate and barium titanate are compared, and the role of polar defects in lithium niobate are studied in the hysteresis loop behavior near domain walls in lithium niobate.Acknowledgements:(1) A portion of this research at Oak Ridge National Laboratory's Center for Nanophase Materials Sciences was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S.Department of Energy(2) Financial support from National Science Foundation is gratefully acknowledged.
5:45 PM - F5.11
Switching Behavior of Magnetically Induced Ferroelectric Domains in MnWO4.
Dennis Meier 1 , Naemi Leo 1 , Michael Maringer 1 , Thomas Lottermoser 1 , Petra Becker 2 , Ladislav Bohaty 2 , Manfred Fiebig 1
1 HISKP, University Bonn, Bonn, NRW, Germany, 2 Institute of Cristallography, University of Cologne, Cologne, NRW, Germany
Show AbstractMaterials with coexisting magnetic and electric order are attracting tremendous attention because these so-called multiferroics often show pronounced magnetoelectric interactions. These interactions are intrinsically strong in spin-spiral multiferroics, where ferroelectricity emerges as a consequence of complex magnetic long-range ordering. Although the related spontaneous polarization is usually small, its robust nature renders these ferroelectrics interesting for future applications. Domains and domain walls are of particular interest, because it is their physics that determine the switching of information bits in memory devices or the coercivity of permanent magnets. However, up to now nearly nothing is known about the domain topology and the switching behavior of these systems.Here we report the controlled manipulation of magnetically induced ferroelectric (FEL) domains in MnWO4. Application of a moderate electric field allows to transform the sample to an electric as well as magnetic single-domain state. In contrast to typical ionic ferroelectrics the spontaneous polarization can be switched without fatigue. This was demonstrated by applying an alternating voltage, while probing the local domain structure by optical second harmonic generation. Even after up to 106 cycles, no defects or pinning effects constrain the movement of domain walls and the ferroelectric hysteresis remains unaltered.Furthermore, a temperature-dependent study of the FEL domain structure reveals an unexpected annealing behavior, that allows to induce a FEL single-domain state by transiently inducing its high-temperature paraelectric phase.In contrast to this, the FEL domain structure is concealed in the paraelectric low-temperature state of MnWO4. The FEL domains are quenched by lowering the temperature below the multiferroic phase boundary but they reemerge with identical topology once the multiferroic phase is re-entered as function of temperature or magnetic field. The local character of this memory effect suggests the paraelectric ground state may retain a component of the spontaneous polarization and thus possess a lower symmetry than commonly assumed.
F6: Poster Session: Functional Characterization and Applications
Session Chairs
Wednesday AM, December 02, 2009
Exhibit Hall D (Hynes)
9:00 PM - F6.10
Surface Magnetostriction Effect Induced Strong Magnetoelectric Coupling in Fe20Ni80/PZN-PT Heterostructure.
Ming Liu 1 , Jing Lou 1 , Ogheneyunume Obi 1 , Kevin Winter 1 , Nay Pwint 1 , Nian Sun 1
1 Electrical and Computer engineering, Northeastern University, Bosotn, Massachusetts, United States
Show AbstractStrong magnetoelectric (ME) coupling in multiferroic composite materials with two constituent phases of ferro/ferrimagnetic and ferroelectric phases has led to electric field manipulation of magnetization [1-4]. Magnetic materials with large magnetostriction and low saturation field are desired for achieving strong ME coupling in composite multiferroic materials. Permalloy with a composition close to Fe20Ni80 is a well known soft magnetic material with near zero magnetostriction in bulk, which is expected to produce minimal ME coupling if permalloy is employed as the magnetic phase in the multiferroic composite. However, for ultra thin Permalloy films, large magnetostriction constant could be induced by surface magnetoelastic effect due to the symmetry restriction at surface and interface, which could enhance ME coupling dramatically. In this work, we will demonstrate this surface magnetostriction effect induced large electric field tuning of magnetization in Fe20Ni80/PZN-PT (lead magnesium niobate-lead titanate) heterostructure. Fe20Ni80 thin films with different thickness (10nm and 100nm) were sputtering deposited on (011) cut single crystal PZN-PT substrate, which has large anisotropic in-plane piezoelectric coefficients. The surface magnetostriction effect induced ME coupling were quantitatively determined by observing Fe20Ni80 film thickness dependence of in-plane ferromagnetic resonance (FMR) field shifts while applying various electric fields through the thickness of PZN-PT. A typical small downward shift of δHr = -20 Oe was observed in 100 nm thickness of Fe20Ni80/PZN-PT due to the near zero magnetostriction constant. However, when the thickness of Fe20Ni80 was reduced to 10 nm, a large downward shift of the ferromagnetic resonance field δHr = -150 Oe was observed, corresponding to ME coefficient of 25 Oe cm/kV. This dramatic enhancement of the ferromagnetic resonance field shift for the Fe20Ni80/PZN-PT heterostructure with 10 nm thick Fe20Ni80 was due to the large surface magnetostriction effect which becomes dominant as reduced thickness. In addition, the electric field dependence of magnetic hysteresis loops for Fe20Ni80/PZN-PT heterostructures with different Fe20Ni80 thickness is consistent with the FMR measurement. Refference:1. M. Liu, O. Obi, J. Lou, Y. Chen, Z. Cai, S. Stoute, M. Espanol, M. Lew, X. Situ, K. S. Ziemer, V. G. Harris, N. X. Sun, Advanced Functional Materials, 19, 1826-1831(2009)2. J. Lou, M. Liu, D. Reed, Y. Ren, and N. X. Sun, Advanced Materials, in press3. M. Liu, O. Obi, J. Lou, S. Stoute, Z. Cai, K. S. Ziemer, N. X. Sun, J. Physics D Applied Physics, 42, 045007 (2009).4. J. Lou, D. Reed, C. Pettiford, M. Liu, Pengdi Han, Shuxiang Dong, N. X. Sun, Appl. Phys. Lett. 92, 262502 (2008)
9:00 PM - F6.11
Electrical Properties of Cr Substituted Multiferroic BiFeO3 Thin Films and the 1T-FET Non-volatile Memory Devices based on BFCO/DSO/Si Heterostructures.
Nishit Murari 1 , Reji Thomas 1 , Ram Katiyar 1
1 Department of Physics, University of PuertoRico, San Juan, Puerto Rico, United States
Show AbstractMultiferroic BiFeO3 (BFO) is under intense investigation as a prospective material for the future memory devices. Metal-ferroelectric-Insulator-semiconductor (MFIS) is the simplest structure in the investigation of material for 1T-FET Random Access Memory application. DyScO3 buffer layer prevents the inter diffusion of ferroelectric in to the silicon and it remains amorphous up 1000°C. Recently, pure BFO in the MFIS structure with DyScO3 buffer layer (Pt/BFO/DyScO3/SiO2/Si) gave excellent results of 1.7V memory window but the retention characteristics were not very encouraging probably due to the high leakage current in BFO. It is reported that Cr substitution in BFO reduces the leakage current and improve the ferroelectric hysteresis behavior. So we fabricated Metal-Insulator-Metal (MIM) on Pt/TiO2/SiO2/Si and MFIS structure (Pt/BFCO/DyScO3/SiO2/Si) utilizing BFO with 5% Cr substitution as ferroelectric material. The chemical solution deposition (CSD) was used to deposit 300 nm BFCO thin film over DyScO3. Circular ( ) platinum dot deposited by DC sputtering was used as top electrodes for the dielectric and ferroelectric measurements. X ray diffraction showed no extra impurity phase, which was further confirmed by the Raman spectroscopy. Most of the Raman active modes of BFO were visible. Atomic force microscopy was used to analyze the surface morphology and surface roughness. Surface of the sample showed uniform grain distribution with roughness of few nano meters. Ferroelectric properties and leakage current were measured using temperature variable probe station. The result showed shift in the Capacitance voltage curve and reduction in leakage current with reducing temperature. Temperature dependent leakages current were studied to understand the conduction mechanism. The MIM structure showed improved ferroelectric loop and reduced leakage current. The behavior may be due to the charge compensation by Cr substitution. Magnetic measurements were done using Vibrational Sample Magnetometer (VSM) which showed the increase in saturation polarization with 5%Cr substitution. So the 5% Cr substitution shows promising multiferroic properties and hence may be of interest in 1T-FET non-volatile memory devices. Results on the MFIS diodes based on BFCO/DyScO3/Si heterostructures will be presented.
9:00 PM - F6.12
In-Situ Nanoscale Observation Of Fatigue In Epitaxially Grown Ferroelectric Thin Films Using Second-Harmonic Piezoresponse Force Microscopy.
Nishit Murari 1 3 , Ramesh Premnath 1 3 , Ho Nyung Lee 2 , Ram Katiyar 3 , Orlando Auciello 1 4 , Seungbum Hong 1
1 Materials Science Division , Argonne National Laboratory, Lemont, Illinois, United States, 3 Department of Physics, University of PuertoRico, San Juan, Puerto Rico, United States, 2 Materials Science & Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 4 Center for Nanoscale Materials, Argonne National Laboratory, Lemont, Illinois, United States
Show AbstractWe studied the fatigue and imprint at the nanoscale on a highly polar epitaxial 60 nm Pb(Zr0.80Ti0.20)O3 (PZT) thin film on SrRuO3 (20nm) / SrTiO3 (001) substrate using second harmonic piezoelectric force microscopy (SH-PFM). We applied 20 Vpp, a voltage greater than the coercive voltage (5 V) with the frequency of 49 kHz to the tip for observing the complete switching and fatigue behavior. We measured the amplitude and phase of 1st and 2nd harmonic responses along with the hysteresis loops at room temperature. We found that clusters of 50-100 nm size with bright and dark contrasts started to appear in 2nd harmonic PFM amplitude images after one scan of 106 cycles of polarization switching, implying local variation of remnant piezoelectric activities as the fatigue developed in the film. Such clusters were not visible in normal PFM using sub-coercive field modulation. Thus we were able to observe the initiation of local fatigue responses by SH-PFM much before the fatigue developed over the whole region and become observable by other methods including normal PFM measurements.
9:00 PM - F6.13
Deciphering Energy Transformation on the Nanoscale.
Oleg Ovchinnikov 1 , Stephen Jesse 2 , Katyayani Seal 2 , Sergei Kalinin 2
1 , University of Tennessee, Knoxville, Tennessee, United States, 2 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show Abstract We developed a system for the identification of disorder type and strength in physical systems based on the recognition analysis of hysteresis loop shape. This approach is based on the modeling of hysteresis loops for a large number of examples uniformly distributed in the parameter space of the system. The thus obtained parameter set is run through a data mining technique called principal component analysis (PCA) which breaks the data in eigenvectors, eigenvalues, and loadings. The use of the PCA on the data set decorrelates the data and helps with the training of the neural network. The PCA loading components are then used to train a feed-forward neural network using the model parameters as a target. The thus trained network is used to analyze the hysteresis loop from a realistic system. The operation of this approach is demonstrated for a 2D random bond – random field Ising model and applied for understanding of switching in polycrystalline ferroelectric capacitors, but it can be universally applied to other systems. The system dynamics are modeled using the generalized random-bond random field Ising model. To match the created hysteresis loops to that of other hysteresis loops and data from realistic systems a feed forward neural network was employed. To make the neural network faster, train and run more efficiently the family of hysteresis loops was converted into eigenvalues λ, eigenvectors w(H) and loadings α using Principle Component Analysis (PCA). This not only decorrelates the data but also allows the training of the network using only these first few which drastically reduces the time and required samples for training.Once the feed forward neural network had been fully trained using a significantly large family of loops, it was used on the data from PZT capacitor. This was done by taking data and using the eigenvectors w(H) from the PCA to project the experimental data set as PR(U)=Σσw(U) . Again, the first few σ contain most of the information about the data. When loadings are run through the neural network it gives J0, δJ, δh that are required for the 2D Ising model to produce the same hysteresis loop as the data. This can be done on large sets of data from realistic systems (e.g. SPM data sets) to produce maps of the (J0, δJ, δh ) for the system. This approach to data analysis using modeling, PCA and neural networks has shown great potential and can be easily applied to analyze many systems.Research was sponsored by the Center for Nanophase Materials Sciences, ORISE HERE program, Office of Basic Energy Sciences, U.S. Department of Energy with Oak Ridge National Laboratory, managed and operated by UT-Battelle, LLC.
9:00 PM - F6.14
Tailored Hysteresis in Ferroelectric-paraelectric Bilayer Capacitors by Tuning Depolarizing Field.
Asif Khan 1 , Pu Yu 2 , Ramamoorthy Ramesh 2 3 , Sayeef Salahuddin 1
1 EECS, UC Berkeley, Berkeley, California, United States, 2 Physics, UC Berkeley, Berkeley, California, United States, 3 Material Science and Engineering, UC Berkeley, Berkeley, California, United States
Show AbstractFerroelectric (FE) thin film heterostructures have been the focus of scientific and industrial research owing to their attractive electrical properties that could be tailored as functional components in novel devices. Fabrication of FE heterostructures together with another functional component either in a bilayer or a multilayer form on a misfitting substrate has opened the gate to new possibilities where the properties of the entire multilayer system can be tuned toward a desired application through component fractions. In FE -paraelectric (PE) bilayer capacitor structures, polarization mismatch gives rise to depolarizing field which can be tuned by varying the volumetric fraction of FE. This in turn may make it possible to controllably change coercive field, remnant polarization and the switching energy of the composite bi-layer capacitor. In this work, a detailed study of this possibility following the phenomenological Landau-Lifshitz-Gilbert formulation will be presented. The effects of domain formation and surface charges on depolarizing field and hence on the electrical properties of the capacitor will be discussed. We have also fabricated atomically smooth epitaxial SrTiO3 /PbZr0.2Ti0.8O3 /SrRuO3 /SrTiO3 heterostructures using pulsed laser deposition as a test vehicle to study and characterize a typical bi-layer system. Initial experimental results and their connections to theoretical predictions will be discussed.
9:00 PM - F6.15
Uncompensated Polarization Charge in Polycrystalline M/Pb(ZrTi)O3/M Structures.
Liubov Delimova 1 , Valentin Yuferev 1 , Igor Grekhov 1
1 Solid State Electronics Division, Ioffe Institute of the Russian Academy of Sciences, St.Petersburg Russian Federation
Show AbstractA polycrystalline Pb(ZrTi)O3 (PZT) film sandwiched between electrodes is known to be the basic element of nonvolatile ferroelectric random access memory where information is stored as a positive or negative remanent polarization P. The bound polarization charge ρ = -divP unavoidably arises at terminations of the film. If the charge is not compensated by free carriers of electrodes, it creates an internal electric field directed opposite to the polarization, which stimulates a depolarization of the film. To prevent this effect, the polarization charge should be compensated by the other shielding charges. In most researches, the screening was studied with neglecting a reciprocal effect of the depolarizing field on the polarization itself, which results in overestimated depolarising field. We deal with well-textured PZT films where columnar PZT grains are separated by ultrathin interlayers of semiconductor PbO phase, forming conducting channels between electrodes. We showed that under certain conditions the uncompensated polarization charge arises at the PZT grain boundaries near electrodes and generates an electric field both inside the PZT grain and PbO channel. This conception explains well the photovoltaic effect which we observed under illumination of short-circuited M/PZT/M capacitors [1]. Here, we study a compensation of polarization charge by free carriers and charged dopants in the PZT film. For this, the two-dimensional theory considering a reciprocal effect of the depolarizing field on the polarization as well as unsaturated hysteresis loop of the polarization in some part of the grain is developed. Using the theory, we show that the depolarizing field strongly depresses the polarization both on grain boundaries and at appreciable distance inside the grain. When polarizing bias is applied to the film, the polarization charge strongly diminishes the electric field on grain boundaries relative to the field inside the grain. As a result, although the field on grain boundary holds its polarizing direction, its value is far reduced. Thus, the grain boundaries are poor polarized just during its polarizing. In polarized and then short-circuited structure, the polarization on grain boundary is capable to change its sign relative to the sign of the polarization inside the grain. This is because the polarization on grain boundary follows minor hysteresis loops, where the coercive strength becomes lower than the electric field. We show that the polarization charge cannot be compensated completely neither by charged dopants in the film, nor by free carriers in semiconductor interlayers, both intrinsic and nonequilibrium. This result differs from the result of Batra [2], who could compensate completely the polarization charge by photoexcited carriers since in the studied single-crystal film there were no conducting channels between the electrodes.1. Appl. Phys. Lett. 91, 112907 (2007).2. P. Wufel and I. P. Batra, Phys. Rev. B8, 5126 (1973).
9:00 PM - F6.16
Towards a High Quality Factor DC Electric Field Switchable Barium Strontium Titanate Solidly Mounted Resonator.
George Saddik 1 , Junwoo Son 2 , Susanne Stemmer 2 , Robert York 1
1 Electrical and Computer Engineering, University of California Santa Barbara, Santa Barbara, California, United States, 2 Materials, University of California Santa Barbara, Santa Barbara, California, United States
Show AbstractVoltage-tunable ferroelectric materials such as barium strontium titanate (BST) have been investigated by several research groups for varactor applications such as tunable matching networks, phase shifters and tunable filters. Recently it has been shown that BST becomes piezoelectric under an applied dc bias. Several research groups have demonstrated BST bulk acoustic wave resonators using the thin film bulk acoustic wave resonator (TFBAR) and solidly mounted resonator (SMR) approaches. Although it is believed that BST thin films can achieve quality factors in excess of 500, typical quality factors for BST SMR devices are in the 40 to 50 range. There are several loss mechanisms that can contribute to low quality factors including acoustic losses in the SMR layers, surface and interface roughness associated with the top and bottom interfaces between the BST layer and the electrodes, and excitation of lateral modes.The goal of this contribution is to investigate the acoustic losses in BST SMR, due to the materials used in the acoustic Bragg reflector (ABR), which is contributing to the low quality factor of our BST SMR devices. Three BST SMRs were designed, and tested, with three different acoustic Bragg reflectors. All Three devices consist of a 4-layer ABR, platinum bottom electrode, BST thin film and a platinum top electrode. The first device had an ABR consisting of W/SiO2/W/SiO2, the second device ABR consisted of Mo/SiO2/Mo/SiO2, and the third device ABR consisted of Pt/SiO2/Pt/SiO2, which has been used in all our previous BST SMR devices. All three devices were measured using a Cascade Microtech probe station, GGB GSG probes, and an E8361A vector network analyzer. The data was collected on all samples from 0 V to 40 V in steps of 5 V. The quality factor of the device with tungsten in the ABR was 101 to 82, for the device with molybdenum in the ABR 88 to 71, and for the device with platinum in the ABR was 1 to 31. The effective electro-mechanical coupling coefficient was 4.1 % at 40 V, 3.9 % at 40 V and 3.4 % at 40 V for the device with tungsten, molybdenum, and platinum samples, respectively. This data clearly shows a significant improvement in the quality factor between the sample with platinum in the ABR and the samples with tungsten or molybdenum in the ABR.
9:00 PM - F6.17
Direct Demonstration of a Charge-driven Magnetoelectric Effect in LSMO/PZT Multiferroic Heterostructures Probed by Near Edge X-Ray Absorption Spectroscopy.
Carlos Vaz 1 2 , Jason Hoffman 1 2 , Yaron Segal 1 2 , James Reiner 1 2 , Zhan Zhang 3 , Charles Ahn 1 2 , Fred Walker 1 2
1 Department of Applied Physics, Yale University, New Haven, Connecticut, United States, 2 Center for Research on Interface Structures and Phenomena (CRISP), Yale University, New Haven, Connecticut, United States, 3 Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractWe recently demonstrated a large magnetoelectric coupling in La0.8Sr0.2MnO3Pb(Zr0.2Ti0.8)O3 (LSMO/PZT) heterostructures, suggesting a way of using the magnetic and electron transport sensitivity of complex oxides to charge in order to devise new multiferroic heterostructures with enhanced coupling between magnetic and ferroelectric order parameters [1]. Such sensitivity is a consequence of the existence of several competing ground states in the electronic phase diagram of complex oxides such as the manganite perovskites. The magnetoelectric effect reported in LSMO/PZT heterostructures has been attributed to a charge-driven change in the Mn valency induced by the ferroelectric polarization, whereby the Mn cations are modulated between a trivalent, high-spin state (S=2) and a tetravalent, low spin state (S=3/2). In this paper, we report the direct observation of the change in the Mn cation valency by means of near edge x-ray absorption spectroscopy in 11 u.c. LSMO/250 nm PZT epitaxial device structures. The epitaxial LSMO films are grown by molecular beam epitaxy and exhibit a well ordered crystalline structure as determined by in situ reflection high energy electron diffraction measurements. The PZT films are grown by off-axis rf sputtering and show good switching properties and low leakage currents. Near edge x-ray scattering measurements reveal a well defined change in the Mn absorption edge with the ferroelectric polarization, giving a direct, quantitative measure of the change in Mn valency in LSMO. The magnitude of the change in valence shows that the charge induced by the ferroelectric polarization modulates only the Mn valence. The large changes in magnetization that are the basis of the magnetoelectric effect observed in these structures are discussed in light of these results.[1] H. J. A. Molegraaf, J. Hoffman, C. A. F. Vaz, S. Gariglio, D. van der Marel, C. H. Ahn, and J.-M. Triscone, Advanced Materials, 2009, in press.
9:00 PM - F6.19
Leakage Current Reduction and Ferroelectric Property of BiFe1-xCoxO3 Thin Films Prepared by Chemical Solution Deposition Using Rapid Thermal Annealing.
TruongTho Nguyen 1 , Takeshi Kanashima 1 , Masanori Okuyama 1
1 Division of Advanced Electronics and Optical Science, Department of Systems Innovation, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka, Japan
Show AbstractMultiferoic BiFeO3 and doped BiFeO3 thin films were reported to have large remanent polarization, but the leakage current density was also quite large, especially at room temperature (RT). In order to improve ferroelectric properties such as decrease of leakage current and increase of remanent polarization at RT, BiFe1-xCoxO3 (BFCO) thin films with good insulation have been prepared on a Pt/TiOx/SiO2/Si substrate by CSD method using rapid thermal annealing (RTA). Bi1.1Fe0.9Co0.1O3 precursor solution was spin-coated and then treated by RTA for 15 minutes at 450 - 550oC in nitrogen. This process was repeated 20 times to obtain the BFCO thin film with thickness about 200 nm.The crystallization of the BFCO thin films was characterized by measurement of the XRD θ-2θ pattern. Rhombohedral BiFeO3 peaks appear in the pattern. The other small peaks are also found and their positions are closed to those of tetragonal Bi7.53Co0.47O11.92 peaks as 10 mol % Bi-excess precursor solution is used for preparation of BFCO thin films. By this procedure of the BFCO thin film preparation, the leakage current density has been decreased with increase of processing temperature. Its leakage current is below 10-6 A/cm2 under the electric field of 1 MV/cm at RT and 80 K. Polarization hystereses were obtained and enhanced in the thin films prepared at the narrow range of temperature, about from 500 oC to 530 oC. The P-E hysteresis loop of the thin film prepared at 500 oC is just saturated if it is measured at low temperature, 80 K. Meanwhile, the BFCO thin film prepared at 530 oC shows good polarization hysteresis loop both at 80 K and RT. It is reinforced that twice the remanent polarization (2Pr) is 169 μC/cm2 at RT, which is larger than that of 140 μC/cm2 at 80 K, when we applied an electric field of 2 MV/cm at 10 KHz. In addition, we also find out that the remanent polarization decreases with increasing frequency at 80 K and 2Pr measured at 0.1 KHz, 0.5 KHz and 20 KHz under 3 MV/cm are 217 μC/cm2, 200 μC/cm2 and 165 μC/cm2, respectively.
9:00 PM - F6.2
Domain Switching Dynamics of Epitaxial BiFeO3 Thin Film using Angle-resolved Piezoelectric Force Microscopy.
Moonkyu Park 1 , Seungbum Hong 2 , Jeffrey Klug 2 4 , Michael Bedzyk 4 5 , Orlando Auciello 2 3 , Kwangsoo No 1
1 Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Daejeon Korea (the Republic of), 2 Materials Science Division , Argonne National Laboratory, Argonne, Illinois, United States, 4 Physics Department, Northwestern University, Evanston, Illinois, United States, 5 Materials Science Department, Northwestern University, Evanston, Illinois, United States, 3 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractWe studied the relationship between domain configuration and polarization switching phenomena in epitaxial BiFeO3 (BFO) thin films by using angle-resolved piezoelectric force microscopy (AR-PFM). We fabricated 40 nm thick BiFeO3 thin films on 125 nm thick SrRuO3 (SRO) / (001) oriented SrTiO3 (STO) single crystal substrates using rf magnetron sputter-deposition. The out-of-plane and in-plane X-ray diffraction (XRD) measurements showed (001)c orientated epitaxial and cube on cube growth of both the BFO and the SRO layers on STO (001) substrates. We obtained the in/out-of phase and amplitude signals while rotating the sample around the film surface normal, from 0o to 180 o with an interval of 30o between each domain image. Subsequently, we measured the local hysteresis loop of the domains variants confirmed by AR-PFM method. In studying the ferroelectric domain configuration and domain switching properties of BFO thin films, we identify the role of in-plane polarization directions in the out-of plane polarization reversals.
9:00 PM - F6.20
New Mechanisms for Multiferroic Order in the Colossal Resistance Manganite PrCaMnO.
Christian Jooss 1 , Joerg Hoffmann 1 , Lijun Wu 2 , Yimei Zhu 2
1 Institute of Materials Physics, University of Goettingen, Goettingen Germany, 2 , Brookhaven National Laboratory, Upton NY 11973, New York, United States
Show AbstractPr1-xCaxMnO3 in the doping range between 0.3 < x < 0.5 represent an extremely interesting manganite system for the study of the interplay of different kinds of ordering (charge, orbital, lattice and spin) and the related colossal resistance effects in external field [1]. High-resolution Transmission Electron Microscopy (TEM) and Electron Diffraction reveal the presence of electronic and structural phase separation in the chemically homogeneous material between an orbital, polaron and charge ordered P21nm phase and an orbital and polaron disordered Pnma phase with paramagnetic insulating behaviour [2]. We establish the presence of Zener polaron (ZP) type ordering which is related to a polar distortion of the MnO6 octahedra, and a localization of oxygen p-hole charge carriers at Mn-O-Mn bonds with preferential bonding angles and lengths [2,3]. Electron holography shows strong evidence for weak ferroelectric order, however, application of sufficient electric fields for polarisation measurements result in a polaron disorder transition to the non-polar Pnma structure. We observe the “melting” of the polaron ordered state via in-situ TEM using a piezocontrolled metal tip for electric stimulation of the material. The polaron ordered phase shows antiferromagnetic order below the Neel temperature. Our study sheds light onto a new mechanism for forming a weak ferroelectric state in a doped manganite material based on softening of a mixed polar/rotational phonon mode and bond-centered ordering of hole carriers at oxygen sites. This may be interpreted as an indication that this manganite system lies on the edge between Mott-Hubbard and Charge-Transfer like behaviour. [1] W. Westhäuser, S. Schramm, J. Hoffmann and Ch. Jooss, Europ. J. Phys. B 53 (2006) 323–331[2] L. Wu, R. Klie Y. Zhu, and Ch. Jooss, Phys. Rev. B 76 (2007) 174210[3] Ch. Jooss, T. Beetz, L. Wu, M. Beleggia, R. Klie, M. Schofield, Y. Zhu, S. Schramm, J. Hoffmann, Proceedings of the National Academy of Science (PNAS) 104 (2007) 13597
9:00 PM - F6.21
Leakage Current of PLD- and CSD-BiFeO3 Thin Films Observed by Current Sensitive AFM.
Seiji Nakashima 1 , Hironori Fujisawa 1 , Jung Min Park 2 , Yukio Hiki 1 , Ryo Nagasoe 1 , Takeshi Kanashima 2 , Masanori Okuyama 2 , Masaru Shimizu 1
1 Grad. School of Engineering, Dept. of Electrical Engineering and Computer Sciences, University of Hyogo, Himeji Japan, 2 Grad. School of Engineering Science, Dept. of Systems Innovation, Osaka University, Toyonaka Japan
Show AbstractMultiferroics have attracted much attention from a viewpoint of practical applications such as memories, sensors and actuators, and perovskite BiFeO3 (BFO) is the leading candidate, which shows good ferroelectric properties in thin film form. We have reported that polycrystalline BFO thin film deposited on Pt/TiO2/SiO2/Si substrate by pulsed laser deposition (PLD) shows giant ferroelectric polarization (Pr ~ 152 μC/cm2) at 80 K1). In spite of its giant Pr, large leakage current and high coercive field (Ec) makes it difficult to realize ferroelectric devices using the lead-free BFO thin films. Especially, large leakage current is one of the most difficult problems, and it has already reported by many workers that the leakage current characteristics are improved by substitution of Ti, Mn, Nd, Cu to Bi or Fe site2). However, cause for the large leakage current has not completely been clarified yet. In this study, we have focused on relationships between leakage current and microstructure or domain structure of BFO thin films, and leakage current mappings of BFO thin films have been performed by current sensitive AFM.350-nm-thick and 250-nm-thick BFO thin films were prepared on Pt/TiO2/SiO2/Si substrate by pulsed laser deposition (PLD) and chemical solution deposition (CSD), respectively. Average grain size of PLD-BFO thin film is about 300 nm, which is the same as the film thickness. From the leakage current mapping at a bias voltage of -10 V, leakage current of the BFO thin film flows through not only grain boundary but also the grain itself. This is quite different from the local leakage current observed in PZT or SBT thin films, in which local current mainly flowed through the grain boundaries. On the other hand, CSD-BFO thin film shows rosette structure and the average grain size is about 30 nm, which is much smaller than film thickness. The rosette structure consists of regions of crystallized in BiFeO3 and amorphous, which has already been reported3). From the leakage current mapping at a bias voltage of -10 V, larger leakage current is observed in crystallized region than amorphous region. Furthermore, leakage current of PLD-BFO thin film is larger than that of CSD-BFO thin film at the same electric field. These results indicate that BFO shows large leakage current as a material characteristic, and the leakage current also flow through the grain boundaries. Reference1)K. Y. Yun, D. Ricinschi, T. Kanashima, M. Noda, and M. Okuyama, Appl. Phys. Lett. 89, 192902 (2006).2)H. Naganuma, J. Miura, S. Okamura, Appl. Phys. Lett., 93, 052901(2008).3)Y. Nakamura, S. Nakashima and M. Okuyama, Jpn. J. Appl. Phys., 47, 7250 (2008).
9:00 PM - F6.22
Magnon Sidebands and Spin-charge Coupling in Bismuth Ferrite Probed by Nonlinear Optical Spectroscopy.
Amit Kumar 1 , Mariola Ramirez 1 , Sava Denev 1 , Xiaoshan Xu 2 , John Ihlefeld 1 , Ying-hao Chu 4 , Janice Musfeldt 2 , Darrell Schlom 1 , Ramamoorthy Ramesh 3 , Venkatraman Gopalan 1
1 Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania, United States, 2 Department of Chemistry, University of Tennessee, Knoxville , Tennessee, United States, 4 Materials Science Divison, Lawrence Berkeley national Lab, Berkeley, California, United States, 3 Materials science and Engineering, University of California Berkeley, Berkeley, California, United States
Show AbstractThe interplay between spin waves (magnons) and electronic structure in materials leads to the creation of additional bands associated with electronic energy levels which are called magnon sidebands. The large difference in the energy scales between magnons (meV) and electronic levels (eV) makes this direct interaction weak and hence makes magnon sidebands difficult to probe. Linear light absorption and scattering techniques at low temperatures are traditionally used to probe these sidebands. Here we show that optical second-harmonic generation, as the lowest-order nonlinear process, can successfully probe the magnon sidebands at room temperature and up to 723 K in bismuth ferrite, associated with large wave vector multimagnon excitations which linear absorption studies are able to resolve only under high magnetic fields and low temperatures. Polarized light studies and temperature dependence of these sidebands reveal a spin-charge coupling interaction of the type PsL2 between the spontaneous polarization (Ps) and antiferromagnetic order parameter, L in bismuth ferrite, that persists with short-range correlation well into the paramagnetic phase up to high temperatures. These observations suggest a broader opportunity to probe the collective spin-charge-lattice interactions in a wide range of material systems at high temperatures and electronic energy scales using nonlinear optics.
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Magnetic Interactions at Py and Magneto-Electric Multiferroic BiFeO3 Interfaces.
John Heron 1 , Chen Wang 2 , Martin Gajek 1 , Dan Ralph 2 , Ramamoorthy Ramesh 1
1 , University of California, Berkeley, Berkeley, California, United States, 2 , Cornell University, Ithaca, New York, United States
Show AbstractBiFeO3 is a ferroelectric and antiferromagnetic multiferroic with these two orders coupled, resulting in the reorientation of the ferroelectric and magnetic domains as applied voltages switch the electric polarization. When a ferromagnet is deposited on the BiFeO3 there is an exchange interaction at the interface that causes the local spins of the ferromagnet to preferentially align with the local spins of the BiFeO3.Permalloy (Py) is the material of choice for spin transfer torque studies due to its low coercivity, low magnetic damping parameter [1], and high spin polarization. With a coefficient of magnetostriction near zero [2], Py is an ideal ferromagnet that can be used to understand the magnetic interface interactions of heterostructures involving magneto-electric multiferroic BiFeO3. Previous studies of Co.9Fe.1/BiFeO3 heterostructures have shown that the magnetic state of the ferromagnetic Co.9Fe.1 layer can be tuned by the ferroelectric domain structure of BiFeO3 [2] as well as electrically switched via the exchange interactions at the interface by switching the domain orientation of the BiFeO3 layer [3]. Controlling the Py layer electrically could lead to the electrical control of Py based spin torque devices. Here we present the magnetic properties of Py layers on BiFeO3 thin films. Exchange bias in these structures has been observed, the magnitude of which directly depends on the BiFeO3 domain structure. The mechanisms of the Py – BiFeO3 interface coupling will be discussed.Work supported by the MURI. [1] G.D. Fuchs et al., Applied Physics Letters 91, 062507 (2007)[2] R. Bonin et al., Journal of Applied Physics 98, 123904 (2005)[2] L.W. Martin et al., Nanoletters 8, 2050 (2008).[3] Y.H. Chu et al., Nature Materials 7, 678 (2008)
9:00 PM - F6.24
Impact of Poling on the Magnetoelectric Effect in P(VDF-HFP)/Metglas Laminates.
Sheng-Guo Lu 1 , Xin Zhou 1 2 , Zhao Fang 1 2 , Qiming Zhang 1 2
1 Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania, United States, 2 Department of Electrical Engineering, The Pennsylvania State University, University Park, Pennsylvania, United States
Show AbstractAs a soft magnetoelectric (ME) coupling device, electroactive polymer/Metglas laminate has been regarded a promising flexible and light ME device used as actuators, detectors, and sensors for magnetic field or electric current. However, the impact of poling on this ME device has not been paid much attention. In this work, the conventional poling and cyclic poling were employed to in-situ pole the poly(vinylidene fluoride – hexafluoropropylene) (P(VDF-HFP)) 90/10 wt% copolymer in P(VDF-HFP)/Metglas laminates. It was found that the poling field in cyclic poling could be at least two times higher than that in conventional poling due to the impact of conduction loss at high temperatures and in high d.c. electric fields for the later one, thus the polarization in cyclic poled P(VDF-HFP) was larger than that using conventional poling. Experimental results indicated that using an electric field of 225 MV/m during cyclic poling, the ME coupling coefficient of the laminates could reach 4 V/(cmOe), almost twice of that using conventional poling. The experiment also turned out that the polarization of P(VDF-HFP) could be further increased with the external electric field during cyclic poling. Therefore, it is possible to further enhance the magnetoelectric coefficient of the P(VDF-HFP)/Metglas laminates through increasing the poling electric field.
9:00 PM - F6.25
Polarization-hysteresis and Non-linear Optical Probing of Strain-enabled Ferroelectricity in CaTiO3 Thin Films.
Eftihia Vlahos 1 , Charles Brooks 1 , Carl Eklund 2 , Michael Biegalski 3 , Karin Rabe 2 , Darrell Schlom 4 , Venkatraman Gopalan 1
1 Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania, United States, 2 Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey, United States, 3 , Oak Ridge National Lab, Oak Ridge, Tennessee, United States, 4 Materials Science and Engineering, Cornell University, Ithaca, New York, United States
Show AbstractCaTiO3, under tensile strain, has been predicted by first principles to be ferroelectric with a spontaneous polarization of up to 0.5 C/m2. Optical second harmonic generation (SHG) was used to determine the transition temperature and symmetry of strained CaTiO3 thin films with strain ranging from -1.7% to 3.3%. Symmetry analysis of the polar plots confirm that for the samples under tensile strain, the polarization is along the <110>p directions, and the point group of the ferroelectric phase is mm2. SHG switching loops were also obtained for the samples under tensile strain. These results are in excellent agreement with the first principles predictions, and the low temperature dielectric measurements that were performed on the same samples. Ferroelectricity was not observed for the sample under compressive strain as predicted by theory. We show using a combination of first-principles and phase-field modeling the coupling and competition between polar distortion and rotational order modes gives rise to such strain asymmetry.
9:00 PM - F6.27
Direct Observation of Capacitor Switching Using Planar Electrodes.
Nina Balke 1 , Martin Gajek 2 , Lane Martin 2 , Ying-Hao Chu 3 , Ramamoorthy Ramesh 2 , Sergei Kalinin 1
1 CNMS, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 , University of California, Berkeley, California, United States, 3 , National Chiao Tung University, Hsin Chu Taiwan
Show AbstractIn most of the applications, the functionality is based on capacitor structures which are manufactured by etching processes. The smallest capacitor structures which are reported by Alexe et al. show capacitor structures down to 100 nm x 100 nm cell size produced by electron beam writing. Understanding the capacitor switching is crucial to determine the application limits, improve the switching process and thus expand the application limits, and make predictions about long-term operations. Typical capacitor investigations include measuring switching currents or polarization P as function of switching field and time. These curves contain information about the switching process and can be used to determine the switching rate limiting switching steps. Due to the shrinking size of capacitor structures and the fact that switching is influenced by the ferroelectric domains in the materials, Piezoresponse Force Microscopy (PFM) became an important tool to characterize ferroelectric capacitors. There are two ways to conduct capacitor experiments. The first one is to use patterned top electrodes and use the PFM tip to contact the electrode and to image domains through the top electrode. The disadvantage of this method is that thickness information are lost and the lateral resolution is reduced. A better way of conducting basic investigations of capacitors switching is a planar electrode structure and use the PFM tip to observe the switching process in-between the capacitor electrodes.Here we report the switching mechanism of capacitors using multiferroic BiFeO3 grown on (110) oriented SrTiO3 as a model system. Planar SrRuO3 electrodes were used to be able to observe the full switching process with a Scanning Probe Microscopy tip. We demonstrate the role of domain nucleation and domain wall motion in the capacitor switching process and show how they can be manipulated using charge injection with the PFM probe. This can be used to pattern large capacitors without the need of etching small capacitors.
9:00 PM - F6.28
Study of Structural, Magnetic and Dielectric Properties of Magnetoelectric TbMn(1-x)Cu(x)O(3).
Shishir Ray 1 , Larry Buroker 1 , Mark Williamsen 1 , Ying Zou 1 , Somaditya Sen 1 , Prasenjit Guptasarma 1
1 , University of Wisconsin Milwaukee, Milwaukee, Wisconsin, United States
Show AbstractTbMnO3 is a magnetoelectric multiferroic system which simultaneously exhibits antiferromagnetism below 40K and ferroelectricity below 28K in the same crystalline phase [1]. Here, we report our study of the crystal structure, magnetic and dielectric properties of TbMn1-x CuxO3, following interesting results of Cu substitution [2] in LaMn1-xCuxO3. Samples of TbMn1-x CuxO3 (0〈x〈0.15) were synthesized using a conventional solid state route. Detailed Rietveld refinement of powder x-ray diffraction data obtained at the 11BM beamline of the Advanced photon source reveals systematic changes in lattice parameters. The effect of Cu substitution on dielectric properties, as a function of frequency and temperature, is minimal. Both Mn3+ and Tb3+ exhibit antiferromagnetic order at lower temperature. An excellent overlap between Zero Field cooled (ZFC) and Field cooled (FC) plots of magnetization versus temperature suggests a less frustrated orthorhombic lattice, and hence a possibility of change in spin chirality compared to unsubstituted TbMnO3. We acknowledge support from NSF and RGI. 1. A.Pimenov et al Nature Physics 2,97-100 (2006).2. Srivastava, S. K. et al Journal of Magnetism and Magnetic Materials, Volume 307, Issue 2, p. 318-324.
9:00 PM - F6.29
Studies of Multiferroic Relaxor Properties of PbFe1/2Ta1/2O3 Thin Films.
Ricardo Martinez 1 , Ratnakar Palai 1 2 , Ram S. Katiyar 1 2
1 Physics, University of Puerto Rico, San Juan PR, Puerto Rico, United States, 2 Institute for Functional Nanomaterials, University of Puerto Rico, San Juan , Puerto Rico, United States
Show AbstractHighly oriented relaxor ferroelectric PbFe1/2Ta1/2O3 (PFT) thin films have been grown successfully on conducting LaSr0.5Co0.5O3 (LSCO) coated (100) oriented MgO by pulsed laser deposition (PLD). The crystal structure, phase purity, and orientation of the thin films were characterized by X-ray diffraction and their surface morphology was observed by Atomic Force Microscopy (AFM). The dielectric properties of PFT thin films, determined in the temperature range from 100 K to 400 K and in the frequency range 1 KHz-1 MHz, were those of typical relaxor ferroelectrics. The maximum dielectric constant was observed at ~168K and 1 KHz. It showed high frequency dispersion, low dielectric constant, shift in dielectric maximum temperature towards lower temperature side and better relaxor properties compare to their bulk counterpart. Hysteresis loop at 100K shows a remnant polarization of ~10mC/cm2 and a coercive field of ~24KV/cm, indicating its application in memory devices. The dielectric tunability of the PFT thin films was ~47% at an applied electric field of 10 V/mm and room temperature. The characteristic relaxation was studied according to Vogel–Fulcher model which indicates perfect relaxor behavior of PFT thin films. Magnetization as function of applied external magnetic field displayed weak ferromagnetic properties at room temperature.Keywords: lead iron tantalate, relaxor ferroelectric, Vogel-Fulcher model.
9:00 PM - F6.3
Resistive Switching Properties of Epitaxial PZT Thin Films on (001) Si by RF Sputtering.
Chun Wang 1
1 Department of Electrical and Computer Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States
Show AbstractEpitaxial PZT (20/80) (001) thin films with TiN bottom electrodes have been deposited on Si(001) single crystal substrates by RF sputtering. The deposited PZT films showed a very smooth surface with roughness of 0.9nm. The orientation relationship was determined to be PZT(001)[110]||TiN(001)[110]||Si(001)[110]. The microstructure and interface of the heterostructure were studied using high resolution transmission electron microscopy (HRTEM). The electron diffraction pattern confirmed the epitaxial relationship between each layer. The current-voltage (I-V) characteristics of the TiN/PZT/TiN/Si sample showed a clear resistive switching. The ratio of the high resistance state over the low resistance state is 200 with an input voltage from –5V to 5V.
9:00 PM - F6.30
Temperature Dependent Micro-Raman Study of Single Crystal Multiferroic Gallium Ferrite.
Somdutta Mukherjee 1 , Rajeev Gupta 1 2 , Ashish Garg 3
1 Department of Physics, Indian Institute of Technology Kanpur, Kanpur, U.P., India, 2 Materials Science Programme, Indian Institute of Technology Kanpur, Kanpur, U.P., India, 3 Materials and Metallurgical Engineering, Indian Institute of Technology Kanpur, Kanpur, U.P., India
Show AbstractGallium Ferrite (GaFeO3), a pyroelectric, piezoelectric and ferrimagnetic material is a promising material for many applications and fundamental studies. Previously reported results on GaFeO3 single crystals show a ferrimagnetic transition in the temperature range 205 K to 250 K depending upon synthesis technique and Fe content. In the present study, we have synthesized GaFeO3 single crystals using the flux growth method using Bi2O3-B2O3 combination flux for the growth. Room temperature X-Ray diffraction pattern of crushed single crystals shows the formation of single phase with orthorhombic structure having a space group Pc21n. Variable temperature micro-Raman measurements have been performed to investigate the behavior and role of phonons across the transitions in the system. Temperature dependent measurements have been carried out in the temperature range 80 K to 575 K. Raman spectra do not present any sudden change in the peak positions or the number of modes present, thus ruling out a structural change. However, we do observe a sudden change in intensity of the modes near 360 cm-1 and 392 cm-1 across the transition boundary. We discuss our results in the context of presence of coupling between the spin and phonon degrees of freedom.
9:00 PM - F6.31
Photoluminescence of Pb(Zr0,52Ti0,48)O3 with Addition of PVA Synthesized by Microwave Assisted Hydrothermal Method.
Maria Zaghete 1 , Guilhermina Teixeira 1 , Gisele Gasparotto 1 , Jose Varela 1
1 Tecnologia, UNESP, Araraquara, São Paulo, Brazil
Show AbstractPZT perovskite powders were synthesized by microwave hydrothermal method (M-H) at 190°C for different times (30min, 2; 4; 8 and 12h) with the presence of aqueous PVA solution 0,36gL-1. Aqueous solution of lead nitrate [Pb(NO3)2], oxyzirconium chloride [ZrOCl2.8H2O], and titanium (IV) isopropoxide C12H28O4Ti were used as starting chemicals. Stoichiometric amounts of lead nitrate and oxyzirconium chloride were mixed with alcoholic solution of titanium (IV) isopropoxide and KOH aqueous solution 1.8 mol.L-1 was used as catalyst of the hydrothermal reaction. M-H heating was done in a microwave digestion system (CEM Corporation - MARS 5 Microwave Accelerated Reaction System). After the M-H treatments the solid and solution phase were separated by centrifugation before characterization. The X-Ray diffraction, SEM-FEG as well as measurements of photoluminescence (PL) emission were used for monitoring the formation of a perovskite phase with random polycrystalline distortion in the structure. Emission spectra, Fig 2, with fixed excitation wavelength 488 nm, showed higher valor to powder obtained with 12h of treatment. A theorical model derived from previous calculations allow us to discuss the origin of the photoluminescence emission in powders can be related to the local disorder in the network of both ZrO6 and TiO6 octahedral, and dodecahedral PbO12. Initial observations of a novel morphology of the PZT perovskite crystal growth as fine plates Fig.3 is directly related to photoluminescence emissions in the lower energy than PZT with cubes morphology that emits in 600nm.
9:00 PM - F6.32
Hyper-Raman Study of Ferroelectric Relaxors.
Ali Al-Zein 1 2 , Jirka Hlinka 3 , Jerome Rouquette 2 , Bernard Hehlen 1
1 LCVN, University Montpellier 2, Montpellier France, 2 Institut Charles Gerhardt (PMOF), University Montpellier 2, Montpellier France, 3 Institute of physics, Academy of sciences of Czech republic, Praha Czechia
Show AbstractHyper-Raman scattering is a non-linear-optic spectroscopy where two incident photons scatter one photon after interaction with an excitation in the media [1]. One major interest of this technique is its high sensitivity to all polar vibrations, including soft polar modes [2], and to excitations that are inactive in both infrared absorption and Raman scattering. These specificities provide hyper-Raman with a very powerful tool for the investigation of local and average structure of ferroelectric-type materials such as relaxors or multiferroic systems. We will focus on hyper-Raman results obtained on three single crystals of the relaxor PbMg1/3Nb2/3O3 (PMN)[3,4]. The relative scattering intensities of the band near 250 cm-1 in various polarization geometries are fully compatible with the hyper-Raman tensor of the F2u ‘silent’ mode of the parent Oh cubic structure. The temperature dependence of the three F1u-symmetry polar modes was investigated between 20 K and 800 K. Some of the transverse (TO) and longitudinal (LO) components are splitted up to the highest temperatures, confirming the existence of local lattice distortions from the cubic symmetry well above the Burns temperature Td ≈ 620 K. The splitting of the LO2-mode strongly increases below Td, a behaviour which likely relates to the growth of the nano-domains. The soft TO-mode is also clearly observed, with a frequency decreasing to zero near Td. Same behaviours have been observed in another relaxor-type compound, PbMg1/3Ta2/3O3. Finally, a weak but clear transition-like anomaly in the temperature dependence of the lowest frequency LO-mode (LO1) is observed near the Curie temperature Tc = 210 K. These experimental observations will be compared to Raman and neutron scattering literature data, and confronted to the proposed scenarios for the evolution of the local structure of PMN with temperature. [1] V. N. Denisov, B. N. Marvin, and V. B. Podobedov, Phys. Rep. 151, 1 (1987). [2] H. Vogt, Coherent and Hyper-Raman Techniques, in Topics in Applied Physics Light Scattering in Solids II, Vol. 50, edited by M. Cardona and G. Güntherdot (Springer, Berlin, 1982).[3] B. Hehlen, G. Simon, and J. Hlinka, Phys. Rev. B 75, 052104 (2007)[4] A. Al-Zein, B. Hehlen, J. Rouquette, and J. Hlinka, Phys. Rev. B 78, 134113 (2008).
9:00 PM - F6.33
Process-dependent Coercive Fields in Undoped and Mn-doped BiFeO3 Films Formed on SrRuO3/Pt(111) Electrodes by rf Sputtering.
Kim Jeong Hwan 1 , Hiroshi Funakubo 1 , Yoshihiro Sugiyama 2 , Hiroshi Ishiwara 1
1 , Tokyo Institue of Technology, Yokohamasi, Kanagawa, Japan, 2 , Fujitsu Laboratories, Atsugi, Kanakawa, Japan
Show AbstractBiFeO3 (BFO) has widely been studied because of its multiferroic properties. It is also a promising candidate for fabricating ferroelectric random access-memory (FeRAM), because it has large polarization and low crystallization temperature. However, BFO has significant problems such as low resistivity and high coercive field at room temperature. In this paper, we prepare undoped BFO and Mn-doped BFO (BFMO) thin films using rf-sputtering on SrRuO3-coated Pt bottom electrodes and subsequent annealing for crystallization. It is shown that the coercive field significantly changes by changing the sputtering conditions of the films.SrRuO3 (SRO) thin films were deposited on Pt(111)/TiO2/SiO2/Si substrates using rf-sputtering in Ar:O2= 70sccm:30sccm at 510°C for 30 minutes. A typical SRO film thickness was 90 nm. Then, BFO and BFMO films were formed on SRO/Pt(111)/TiO2/SiO2/Si substrates using rf-sputtering. Two substrate temperatures of 450 and 550°C were used and in the former case the deposited films were subsequently annealed for crystallization at 650°C for 10 minutes in O2 flow. Lastly, Pt top electrodes were deposited using electron-beam evaporation. In P-E hysteresis loops of BFO thin films deposited on SRO/Pt by rf-sputtering at 550°C, the lowest coercive field is obtained in a BFO film deposited on the SRO/Pt electrode at 450°C and post-annealed at 650°C in O2 for 10 min. The shapes of the hysteresis loops are close to rectangular. The remanent polarizations (Pr) of 550°C-deposited and post-annealed BFO films on SRO/Pt(111) electrodes are approximately 90 and 68 μC/cm2, respectively. The coercive field in the post-annealed BFO film (2Ec= 489 kV/cm) is approximately 60 % smaller than that in the 550°C- deposited BFO film (2Ec= 1246 kV/cm). In 5% Mn-substituted BFO film (triangles), Pr and 2Ec are 46 μC/cm2 and 686 kV/cm, respectively, for a 185 nm-thick BFMO film on SRO/Pt(111). The coercive voltage (2Vc) of the BFMO film is 12 V for an applied voltage of 17 V. In J-E characteristics of the same samples, the current density at a certain electric field is much higher in the post-annealed BFO film than that in the 550°C-deposited BFO films. However, when the applied electric field is normalized by the coercive field, the current density values become comparable between the two samples. The leakage current density in the BFMO film is lower in the high electric field region than those in the BFO films. We conclude from these results that the coercive field in RF-sputtered BFO and BFMO films can be much reduced by optimizing the sputtering conditions as well as the target composition.
9:00 PM - F6.34
Broadband Dielectric Spectroscopy of Strained Ruddlesden-Popper Series Sr(n+1)Ti(n)O(3n+1) (n = 2, 3, 4, 5) Thin Films.
Nathan Orloff 1 2 , C. Lee 3 4 , M. Bernhagen 5 , R. Uecker 5 , C. Fennie 6 , X. Xi 4 , D. Schlom 3 , I. Takeuchi 2 , J. Booth 1
1 EEEL, NIST, Boudler, Colorado, United States, 2 Materials Science and Engineering, University of Maryland, College Park, Maryland, United States, 3 Materials Science and Engineering, Cornell University, Ithaca, Pennsylvania, United States, 4 Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania, United States, 5 , Institute for Crystal Growth, Berlin Germany, 6 School of Applied and Engineering Physics, Cornell University, Ithaca, Pennsylvania, United States
Show AbstractWe have measured the frequency dependent permittivity of 50 nm thick Ruddlesden-Popper Sr(n+1)Ti(n)O(3n+1) (n = 2, 3, 4, 5) thin films as a function of temperature and dc electric-field. The strain was achieved by growing the films on DyScO3 substrates by MBE. The on-wafer metrology of thin-films as a function of frequency is essential for the eventual integration of new materials into microwave devices and commercial products. Interdigitated capacitors and coplanar waveguides are measured to extract frequency response from 100 Hz to 40 GHz. At room temperature, the permittivities obtained for strained Sr(n+1)Ti(n)O(3n+1) (n = 3, 4, 5) were 72, 382, and 597, respectively, and were independent of frequency. These values are shown in contrast with previously obtained results for unstrained n = 1, 2, and 3 films grown on LSAT substrates with permittivities of 42, 54, 77, respectively. (Orloff et al., Appl. Phys. Lett. 94, 042908 (2009)). At low temperatures the strained n = 3, 4, and 5 films undergo paraelectric-ferroelectric phase transitions at around 60 K, 130 K, and 175 K, respectively. The films show a dramatic increase in permittivity and marked frequency dispersion near the Curie temperature. Electric-field tunability measurements at and around the Curie temperature as a function of frequency will also be reported.
9:00 PM - F6.35
Strain-induced Relaxor Behavior of Ferroelectric Thin Films.
Margarita Correa 1 , Ashok Kumar 1 , Ram Katiyar 1
1 Physics, University of Puerto Rico, San Juan, Puerto Rico, United States
Show AbstractWe have fabricated Pb(Sc0.5Nb(1-x)/2Tax/2)O3 (0 ≤ x ≤ 1) ferroelectric thin films on single crystalline (100) MgO substrate with a La0.5Sr0.5CoO3 (LSCO) layer as a bottom electrode by pulsed laser deposition technique. Films were single phase perovskite with in-plane orientation along (100) direction. Dielectric properties were measured as a function of frequency (100 Hz to 1 MHz) and temperature (100 to 650 K). The temperature evolution of dielectric constant showed broad diffuse phase transition (DPT) with frequency dispersion of these ferroelectric thin films in the full compositional range. The frequency dispersion of dielectric constant follows the Vogel-Fulcher law for relaxor which gives activation energies between 0.00388 and 0.00914 eV. Although, these films have a disordered macrostructure each of them showed striking features on their microstructure, dielectric and polarization properties depending of the concentration of Nb and Ta ions. Those films with x≤0.5 exhibited frequency dispersion at low frequencies range (100 Hz to 50 KHz) with the maximum of transition temperature (Tm) shifted towards lower frequency for about 40 degrees, while for higher frequencies Tm suffers an exaggerated shift. The polarization hysteresis loops of these films were slim in the vicinity of the DPT and become well saturated and well defined on decreasing temperature. High Resolution Transmission Electron Microscope (HRTEM) studies of these films illustrated small polar nanoregions surrounding by bigger disordered regions. In the case of films with higher x values (x>0.5), the frequency range of the frequency dispersion was high (1 to 1000 kHz) with a Tm shift of about 50 degrees. However, their polarization hysteresis loops were slim without significant change with temperature at the same time their HRTEM show mainly an ordered microstructure which may support the invariant nature of polarization hysteresis. When we compare the dielectric and microstructural properties of these films with ceramics in the same compositional range, we found that those materials with normal ferroelectric behavior in bulk form showed relaxor behavior in thin films, and those with relaxor response in bulk exhibited an enhanced relaxor behavior (more frequency dispersion) in films. We also found a systematic shifting of Tm to lower temperature side for each film respect to their bulk counterpart that is due to the compressive strain in films.
9:00 PM - F6.36
Stability and Transition Mechanisms of Polarization States in Ultra-thin PbTiO3 Controlled by Ionic Surface Compensation.
Matthew Highland 1 , Timothy Fister 1 , Marie-Ingrid Richard 1 , Dillon Fong 1 , Jeffery Eastman 1 , Stephen Streiffer 1 , Paul Fuoss 1 , G. Brian Stephenson 1 , Carol Thompson 2
1 , Argonne National Laboratory, Argonne, Illinois, United States, 2 Department of Physics, Northern Illinois University, DeKalb, Illinois, United States
Show AbstractOne of the primary size effects on polarization stability in ferroelectric films arises because of the requirement for compensation of the polarization discontinuity at the interfaces. We have found that alterations of the surface charge compensation due to changes in the chemical environment can control the polarization orientation in ultra-thin PbTiO3 films. In this talk we present measurements of the stability limits of, and transition mechanisms between, states of different polarization orientation. Synchrotron x-ray scattering is used to determine the equilibrium polarization structure and dynamics of epitaxial PbTiO3 films on conductive SrRuO3 layers coherently strained to SrTiO3 (001) substrates as a function of temperature, film thickness, and external oxygen partial pressure (pO2). For films thinner than 4 to 8 nm, depending upon temperature, we observe that polarization switching driven by pO2 changes occurs by a continuous (rather than nucleated) mechanism. This suppression of nucleation can be explained by a model taking into account the slow equilibration time for ionic surface compensation. We also observe that the ambient chemistry affects the equilibrium polarization phase diagram, suppressing TC at intermediate values of pO2. Work supported by the U.S. Department of Energy under Contract No. DE-AC02-06CH11357.
9:00 PM - F6.37
Particle Size Effect of Sinter-forged NaNbO3 Ceramics on the Frequency-dependent Dielectric Characteristics.
Reji Thomas 1 , Christian Pithan 2 , Y. Shiratori 3 , Rainer Waser 2 , Ram Katiyar 1
1 Department of Physics and Institute for Functional Nanomaterials, University of Puerto Rico, San Juan, Puerto Rico, United States, 2 Institute für Festkörperforschung (IFF) and Center of Nanoelectronic systems for Information Technology (CNI), Research Centre Jülich, Juelich, D-52425, Germany, 3 Department of Chemical System Engineering, The University of Tokyo, Tokyo, 113-8656, Japan
Show AbstractThe toxicity of lead is a serious threat to human health and environment, thus developing lead-free piezoelectrics as an alternative to most widely used lead zirconium titanate (PZT) is of great importance. Among several candidates for lead-free materials, NaNbO3-based ceramics have been considered to be promising candidates and are examined here. NaNbO3 nano-particles were prepared by micro-emulsion mediated synthesis and sinter-forged at 1000°C to make the pellet for the electrical characterization. The sinter-forged pellets were annealed at temperatures between 925 and 1000°C for one hour to systematically increase the average grain-size from a several hundred nanometer (nm) up to few micrometer (μm) in the bulk ceramics. Structural characterization including the observation by electron microscopy in combination with X-ray diffraction and temperature tuning Raman-spectroscopy revealed that the ceramic samples consisted of a phase mixture of the anti-ferroelectric polymorph of NaNbO3 (Space group: Pbcm) and a new polar modification (Space group: Pmc21), its volume content being depended on the average grain-size. For this reason detailed dielectric characterization is of great importance and form the basis of this presentation. NaNbO3 shows six structural phase transitions between ferroelectric (FE), antiferroelectric (AFE) and nonferroelectric phases in the temperature range 150K- 900K. Impedance spectroscopy (complex dielectric permittivity and dielectric modulus) on sinter-forged NaNbO3 ceramics in the frequency range of 100 Hz to 1 MHz at various temperatures (100–700 K) has been carried out to study effect the structural phase transition on the dielectric properties. Since the dielectric property depends on the grain size, these measurements were performed on pellets with average particle size 320 nm (NNO-320), 550 nm (NNO-550) and 750 nm (NNO-750). Room temperature dielectric constant and loss tangent at 1MHz were 340 and 0.008, 264 and .009, 219 and 0.01, respectively, for NNO-320, NNO-550, NNO-750 samples. AC conductivity and dielectric constant shows temperature and frequency dependence. The mechanism of conduction will be discussed based on the existing theoretical models.
9:00 PM - F6.39
ZnO-BaTiO3-ZnO: Unipolar Ferroelectric Transistor Structures with Spontaneous Interface Charge Coupling for Non-volatile Switching Applications.
R. Voora 1 , Tino Hofmann 1 , M. Brandt 2 , M. Lorenz 2 , M. Grundmann 2 , N. Ashkenov 2 , M. Schubert 1
1 , University of Nebraska-Lincoln, Lincoln, Nebraska, United States, 2 , Universität Leipzig, Leipzig Germany
Show AbstractHeterostructures composed of perovskite-structure BaTiO3 and wurtzite-structure ZnO layers reveal interface charge coupling, which can be employed for non-volatile memory architectures [1]. The ferroelectric state in triple layer structures can be used to switch the reverse current in unipolar transistor architectures, which possess asymetric spontaneous interface charge distribution. Here we report on capacitance-voltage, current-voltage, Sawyer-Tower, and transient current switching behavior of ZnO-BaTiO3-ZnO heterostructures deposited on (001) silicon by using pulsed laser deposition. The triple-layer structure reveals asymmetric capacitance- and current-voltage hysteresis and cycling-voltage dependent Sawyer-Tower polarization drift. We explain our findings by coupling of the ferroelectric (BaTiO3) and piezoelectric (ZnO) interface charges and parallel polarization orientation of the ZnO layers causing asymmetric space charge region formation under positive and negative bias. Generalized dielectric continum model calculation augmented by bias-dependent space charge depletion formation corroborates our findings. The transient current characteristics suggest use of this structure as novel non-volatile memory device.[1] R. Voora et al., Appl. Phys. Lett. 94, 142904 (2009).
9:00 PM - F6.4
Electrical Properties of BaTiO3(PZT)/SrTiO3/BaTiO3(PZT)/SrTiO3 Multilayer Films on Silicon Substrate for MEMS Devices.
Ozgul Yasar 1 , Rajini B. Konda 1 , Rajeh M. Mundle 1 , Frances Williams 1 , Aswini Pradhan 1
1 , Norfolk State University, Norfolk, Virginia, United States
Show AbstractMicroelectromechanical Systems (MEMS) devices, which are also called micromachines play an important role to get wider distribution of an easier access information, compatible life style with environment, and improve in social welfare. The ferroelectric and piezoelectric materials have attracted attention for MEMS devices especially for memory and various sensors systems. This research presents the development of properties of Barium titanate (BaTiO3) for MEMS devices. Barium titanate (BaTiO3), Strontium titanate (SrTiO3), and Lead zirconate titanate (PZT) were used for this research. Magnetron Sputtering and Pulsed Laser Deposition (PLD) techniques were used to prepare two different samples which were BaTiO3/SrTiO3/BaTiO3/SrTiO3 and SrTiO3/PZT/SrTiO3/PZT on platinized silicon substrates. Pt was deposited as a bottom and top electrode to measure the polarization of these multilayer samples. BaTiO3 and PZT are ferroelectric materials. This research investigated to ferroelectric behaviors of multilayer BaTiO3 sample to be used in MEMS devices instead of PZT. Ferroelectric properties and surface morphology were compared for BaTiO3/SrTiO3/BaTiO3/SrTiO3 and SrTiO3/PZT/SrTiO3/PZT samples with using X-Ray diffraction (XRD), Atomic Force Microscopy (AFM), Transmission Electron Microscopy (TEM) and Probe Station which was connected to Ferroelectric Tester. Our results demonstrated that all the multilayer synthesis display enhanced polarization property, which may be useful for potential applications.
9:00 PM - F6.40
Observation of Magnetoelectric Coupling in Hexagonal YMnO3 via Infield Neutron Diffraction Experiment.
Anil Singh 1 , S. Kaushik 2 , V. Siruguri 2 , S. Patnaik 1
1 School of Physical Sciences, Jawaharlal Nehru University, New Delhi, Delhi, India, 2 UGC-DAE-Consortium for Scientific Research Mumbai Centre, Bhabha Atomic Research Centre, Mumbai, 400085, India
Show AbstractMultiferroic materials, that offer the possibility of manipulating an ordered electric (magnetic) state by applying magnetic (electric) field, have attracted considerable attention in the recent past. Here we report a detailed analysis of structural, magnetic, thermodynamic and dielectric properties of polycrystalline samples of YMnO3. This material belongs to space group P63cm with hexagonal crystal structure and was synthesized by solid state reaction method. We have carried out extensive zero field and in-field neutron diffraction measurements as a function of temperature. Our study provides evidence for change in the lattice parameters, ordered magnetic moment, Mn-O bond lengths, O-Mn-O bond angles and hence the tilting of MnO5 pollyhedra as a function of temperature and magnetic field. We also study the magnetoelectric coupling in YMnO3 by field dependent dielectric measurements. A distinct anomaly near Neél temperature is observed in these measurements that vary with the application of magnetic field. The change in dielectric constant with magnetic field is attributed to reduction in tilting of MnO5 pollyhedra. In essence, we develop an understanding of microscopic origin of magnetoelectric coupling of geometrically frustrated antiferromagnetic multiferroic YMnO3 with their field dependent magnetic structure.
9:00 PM - F6.41
High Density Capacitors Based on Amorphous BaTiO3 Layers Grown Using Pulsed Laser Deposition Technique with Hydrogen as a Process Gas.
Rajini Konda 1 , Alex Lee 1
1 Materials Science, Norfolk State University, Norfolk, Virginia, United States
Show AbstractAbstract: Ferroelectric Barium Titanate (BaTiO3) amorphous films have been grown on metalized Silicon and Glass substrates at low temperatures (200oC) using Pulsed Laser deposition(PLD) technique. For the metallization standard sputtering technique was used and molybdenum and platinum were deposited as metallization layers at room temperature. The surface morphological studies of these BaTiO3 films on Pt/Si substrates reveals that the roughness increases as thickness of the film increases due to grain growth. The structural characteristics have been studied using X-ray diffractometer which shows that the films are amorphous in nature. The BaTiO3 films have been grown in the presence of hydrogen gas with the intention that hydrogen incorporates in amorphous BaTiO3, leading to a proton conducting ceramic. We expect such a material has interesting properties for super capacitors applications. In addition to these applications the present work is also expected to help in understanding hydrogen related defects such as point defects ( interstitials, vacancies) in perovskite titanates.
9:00 PM - F6.43
Phonon Anomalies at the Magnetic Phase Transitions in BiFeO3 Thin Films.
Manoj Singh 1 , S. Dussan 1 , Ram Katiyar 1
1 Physics, University of Puerto Rico, San Juan, Puerto Rico, San Juan, Puerto Rico, United States
Show AbstractRaman spectra of epitaxal BiFeO3 (BFO) thin films, grown on (111) SrTiO3 substrates, have been studied in temperature range 80K - 800K. All three prominent A1-symmetry (138, 170, and 214 cm-1) Raman modes show evolution with the temperature near the Néel temperature(TN ), which is interpreted due to spin phonon coupling and it could be also linked with the structural instability originated by octahedral tilting near Neet temperature (TN) as reported by A. Palewicz et al Acta Cryst B 63, 537(2007). The observed anomalous enhancements in Raman intensity below 200K reveals spin reorientation transition due to change in the magnetic spin ordering.
9:00 PM - F6.45
Effects of Si Surface Nitridation and Oxynitridation on Pt/SrBi2Ta2O9/HfO2/Si Ferroelectric-gate FETs.
Mitsue Takahashi 1 , Takeshi Horiuchi 1 , Shigeki Sakai 1
1 , National Institute of Advanced Industrial Science and Technology, Tsukuba Japan
Show AbstractA metal/ferroelectric/insulator/semiconductor (MFIS) field effect transistor (FET) is a kind of ferroelectric-gate (Fe) FETs which are attracting much attention by their promising applications to both nonvolatile logic and memory circuits [1,2]. A Pt/SrBi2Ta2O9(SBT)/HfO2/Si MFIS FET is one of the FeFETs with good data-retention characteristics [3], but when the MFIS FET will meet the industrial demands for low voltage operation, the present fabrication process need a modification for keeping large memory windows even by the low voltage operation. For obtaining a large memory window of the Pt/SBT/HfO2/Si FeFET, equivalent oxide thickness (EOT) of the HfO2 and an interfacial layer (IL) should be reduced in order to give a sufficiently large part of the gate voltage to the SBT. The IL consists of SiOx grown between the Si and HfO2 during an 800°C post-annealing for the SBT poly crystallization. In this study, effects of Si surface nitridation and oxynitridation on Pt/SBT/HfO2/Si FeFETs were investigated. We performed rapid thermal nitridation (RTN) of the Si substrates in NH3. SiNx/Si substrates were made only by this RTN of Si. SiON/Si substrates were prepared by rapid thermal oxidation of the Si followed by the RTN. In fabricating the SiNx/Si substrates, the RTN was performed at various temperatures ranging from 800 to 1190°C. When the RTN temperature was 1080°C, the Pt/SBT/HfO2/SiNx/Si FeFETs showed the largest memory window of 1.3V at scanning gate voltages 1±5V, which was larger than those of the conventional Pt/SBT/HfO2/Si FeFETs. Studies by transmission electron microscopy, secondary ion mass spectrometry and electrical properties indicated that the increased dielectric constant of the IL by the RTN successfully widen the memory window. However, a problem of the Pt/SBT/HfO2/SiNx/Si FeFETs was that they tended to show drain current - gate voltage (Id-Vg) curves with larger subthreshold swing (S) than the Pt/SBT/HfO2/SiNx/Si FeFETs. To solve the problem, we performed rapid thermal oxidation of the Si before the RTN and fabricated Pt/SBT/HfO2/SiON/Si FeFETs. The FeFETs showed very steep Id-Vg curves with S=90mV/decade, when the RTN temperature was about 1000°C. Moreover, their memory windows were larger than those of FeFETs with conventional Pt/SBT/HfO2/Si and the Pt/SBT/HfO2/SiNx/Si processed by the RTN only, especially at small scanning gate voltages within 1±4V. The results indicated that the oxynitridation of the Si was most effective for reducing the EOT of the IL in Pt/SBT/HfO2/Si FeFETs with keeping good interfaces on the Si substrates. [1]M. Takahashi, et al., IEICE Electronics Express, in press. [2]S. Sakai, et al., Proc. of the 2008 23rd IEEE Non-Volatile Semiconductor Memory Workshop, pp.103-105. [3] S. Sakai, et al., 2004 IEEE IEDM Technical Digest, pp.915-918, 2004/12.
9:00 PM - F6.46
Nonvolatile Logic Circuit Application of Ferroelectric Gate FETs.
Shigeki Sakai 1 , Mitsue Takahashi 1
1 , National Institute of Advanced Industrial Science and Technology, Tsukuba Japan
Show AbstractA nonvolatile logic circuit, which is a logic circuit with nonvolatile-memory function, is one of interesting applications of ferroelectric-gate field effect transistors (FeFETs). The nonvolatile logic circuits of the FeFETs are called ferroelectric complementary metal-oxide-semiconductor (FeCMOS) circuits, which are CMOS circuits composed of the FeFETs instead of conventional MOS FETs. For the FeCMOS application, the unique characters of the FeFETs were used, which are working as logic transistors by small applied voltages and as nonvolatile memory transistors by large applied voltages. Both n- and p-channel-type (n-ch and p-ch) FeFETs were constructed on a same Si substrate with double n- and p-well structures made by ion implantations. For wiring the FeFETs, an insulator and metal layers were prepared over the FeFETs and patterned by photo-lithography. As an example of the FeCMOS, a double-stage inverter circuit was fabricated for demonstrating a series of regular operations such as logic, data write, sleep without any voltage supply and nondestructive read. Supply voltages to the first and second inverters were (VH1, VL1) and (VH2, VL2), respectively. The circuit was composed of Pt/SrBi2Ta2O9/(HfO2)0.75(Al2O3)0.25/Si FeFETs. In logic operation, supply voltages were VH1=VH2=Vcc0 and VL1=VL2=Vss0, where the Vcc0 and Vss0 were -0.3±1.0V. Input signal Vin was also swung between the Vcc0 and Vss0. The n-ch and p-ch FeFETs worked as conventional logic transistors because the voltage differences between the gates and the substrates (Vg-sub) were small enough to show negligibly narrow memory windows in their drain current (Id)-Vg-sub curves. In write operation, only the VH1 and VL1 were changed. The VH1 was raised from Vcc0 to Vcc1 and the VL1 was reduced from Vss0 to Vss1. The Vcc1 and Vss1 were -0.3±3.4V. These operations expanded the Vg-subs of the n-ch and p-ch FeFETs in the second inverter. Thus the FeFETs memorized their on- and off-states. In sleep operation, no voltages were supplied, VH1=VH2=VL1=VL2=Vin=0V. In read operation, only the VH2 and VL2 were restored to Vcc0 and Vss0. The output signal Vout was nondestructively read out. The Vout retention times integrated from the write end were measured up to 30.5 hours for the high Vout and 41 hours for the low Vout. Pulse endurance corresponding to repeated logic-operations was much better than that to repeated write-operations. The results indicated that FeCMOS meets the needs of prospective nonvolatile logic circuits for saving power consumption, which will be used mostly as a conventional logic and occasionally as a nonvolatile memory on demand. The FeCMOS may enable us to realize quick-on-and-off computers or digital electronic devices with ultra-low power consumptions. This work was partially supported by the New Energy and Industrial Technology Development Organization (NEDO).
9:00 PM - F6.5
Ferroelectric Switching Behavior of (001) Mono-domain BiFeO3 Thin Films.
Seung Hyub Baek 1 , Ho-Won Jang 1 , Chad Folkman 1 , Chang-Beom Eom 1 , Yulan Li 2 , Benjamin Winchester 2 , Long-Qing Chen 2 , Jinxing Zhang 3 , Ying-Hao Chu 3 , Ramamoorthy Ramesh 3 , Christopher Nelson 4 , Xiaoqing Pan 4
1 Materials Science and Engineering, UW-Madison, Madison, Wisconsin, United States, 2 Materials Science and Engineering, Penn State University, University Park, Pennsylvania, United States, 3 Materials Science and Engineering, UC-Berkeley, Berkeley, California, United States, 4 Materials Science and Engineering, Univ. Michigan-Ann Arbor, Ann Arbor, Michigan, United States
Show Abstract BiFeO3 has drawn a great deal of attention as a room-temperature multiferroic material to control magnetic property by applying electric field for the magneto-electric device. BiFeO3 has magneto-electric coupling between [111] spontaneous polarization and (111) anti-ferromagnetic plane. Due to its rhombohedral symmetry, there exist three polarization switching paths in the (001) BiFeO3 films under vertical electric field: 180o, 109o and 71o. Among these, either 71o or 109o switching can induce magneto-electric coupled switching. Therefore, it is desirable to control selectively 71o or 109o switching while avoiding 180o switching. In order to understand switching path, we have used (001) mono-domain single crystal BiFeO3 thin films as a simple and clean model. Our experimental and theoretical results exhibit that 71o switching is kinetically favored, but transformed to 180o switching with time to reduce ferroelastic energy. This behavior hinders from realization of non-volatile magneto-electric devices. We have successfully overcome this relaxation problem by making BiFeO3 islands to remove ferroelastic interaction between the switched and unswitched region. This work provides a model and design-tools to control magneto-electric coupling in low-symmetry multiferroics.
9:00 PM - F6.6
Microscopic Observation of Suppressed Polarization Switching in Epitaxial (001) BiFeO3 Thin Films.
Jae-Wan Park 1 , Seung-Hyub Baek 1 , ChungWung Bark 1 , Chang-Beom Eom 1
1 Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States
Show AbstractA multiferroic BiFeO3 has attracted much attention because of its promising applications to nonvolatile memory and magnetoelectric devices. The rhombohedral BiFeO3 has four possible structural (ferroelastic) variants and eight possible polarization (ferroelectric) variants due to its low symmetry of unit cell structure. Recently, it was reported that the epitaxial BiFeO3 thin film grown on a vicinal substrate exhibited 2-variants domain structure and its ferroelectric and leakage properties were superior to those of BiFeO3 thin film with 4-variants domain grown on an exact substrate. In this study, we report the microscopic observation of suppressed polarization switching in the epitaxial (100) BiFeO3 thin films with 4-variants domain structures. From the polarization switching of BiFeO3 thin films by a piezoelectric force microscopy, it was found that ferroelectric domains surrounded by 109° and/or 180° domain walls were not switched. By a repetitive switching, however, these unswitched domains were completely switched and the remnant polarization finally reached to the intrinsic value of BiFeO3 thin film. These results suggest that the origin of suppressed polarization switching in BiFeO3 thin film is related to the ferroelectric domain pinning by 109° and 180° domain walls which can be dominant leakage paths.
9:00 PM - F6.7
Ferroelectric Domain Switching Dynamics at Macroscopic Geometric and Strained Defects.
Nicholas Polomoff 1 , Sungjun Lee 1 , Ying-Hao Chu 2 , Pu Yu 3 , Ramamoorthy Ramesh 3 , Bryan Huey 1
1 Institute of Material Science, University of Connecticut, Storrs, Connecticut, United States, 2 , National Chiao Tung University, Hsin Chu Taiwan, 3 Dept. of Physics, University of California Berkeley, Berkeley, California, United States
Show AbstractHigh Speed Piezo Force Microscopy (HSPFM) is employed to directly investigate polarization switching dynamics for two model macroscopic defects that are representative of practical ferroelectric device architectures and/or flaws: at the edge of a capacitive structure, and at nanoindentation sites. Specifically, polarization reversal is reported both on the capacitor and on the adjacent exposed film. This includes movies of the distinct switching mechanisms, as well as maps of spatially resolved hysteresis loops. Electrical P-E measurements are also reported for the same capacitors for comparison. Finally, domain nucleation and growth are similarly characterized at nano-indentation sites for the same film, shifting the boundary conditions for geometry and strain. Such studies are complementary to recent results elsewhere on the sometimes profound influence of capacitor geometry and macroscopic flaws, with the additional insight of simultaneous switching in the surrounding film that is available through the efficiencies afforded by HSPFM.
9:00 PM - F6.8
Increase of the Magnetoelectric Voltage Coefficients of Metglas/Polyvinylidene fluoride Laminar Composites Using the Flux Concentration Effect.
Zhao Fang 1 2 , Shengguo Lu 2 , Qiming Zhang 1 2 , Mario Tahchi 3
1 Department of Electrical Engineering, The Pennsylvania State University, University Park, Pennsylvania, United States, 2 Material Research Institute, The Pennsylvania State University, University Park, Pennsylvania, United States, 3 Department of Physics, Lebanese University, Jdeidet Lebanon
Show AbstractThe magnetic flux density inside a Metglas sheet is high due to its high magnetic permeability, which is known as the magnetic flux concentration effect. Magnetic flux concentration of Metglas as a function of its sheet aspect ratio was investigated for Metglas/Polyvinylidene fluoride (PVDF) laminar composites. Both the simulations and experimental results suggest that the magnetic flux concentration effect is markedly enhanced when the aspect ratio (cross-section width/length) of a Metglas sheet is reduced. Consequently the magnetostriction of Metglas and the magnetoelectric (ME) voltage coefficients of the laminar composites are enhanced for a small aspect ratio of the Metglas sheet. The ME voltage coefficient for a laminar composite with 1 mm wide and 30 mm long Metglas sheet (25 μm thick) is 21.46 V/cm*Oe, which is much higher than those reported earlier in similar laminar composites without making use of the flux concentration effect. To take advantage of this effect, a custom-made voltage mode read-out IC was integrated with the laminar composite to obtain the ME signals. The results demonstrate an effective means to significantly enhance the sensitivity of the magnetostrictive/piezoelectric composites, thus facilitating them as weak magnetic field sensors.
9:00 PM - F6.9
Tunneling Electroresistance Effect in Ferroelectric Tunnel Junctions with a Composite Barrier.
Mikhail Zhuravlev 1 2 , Yong Wang 1 , Sadamichi Maekawa 3 , Evgeny Tsymbal 1
1 Department of Physics and Astronomy, University of Nebraska-Lincoln, Lincoln, Nebraska, United States, 2 Kurnakov Institute for General and Inorganic Chemistry, Russian Academy of Sciences, Moscow Russian Federation, 3 Institute for Materials Research, Tohoku University, Sendai Japan
Show AbstractFerroelectric tunnel junctions have recently attracted significant interest due to the interesting physics controlling their functional behavior and their potential for applications in novel electronic and spintronic devices [1]. Contrary to ferroelectric capacitors where leakage currents are detrimental to the device performance, the conductance of a FTJ is the functional characteristic of the device. The key property is tunneling electroresistance (TER) that is the change in resistance of a FTJ with reversal of ferroelectric polarization. Based on simple models it was predicted that TER in FTJs can be sizable due to the change in the tunneling potential barrier dependent on polarization orientation [2,3]. These results were elaborated using first-principles calculations of transport properties of FTJs [4,5]. Here we propose an efficient way to enhance the TER considerably by using a layered composite barrier combining a functional ferroelectric film and a thin film of a non-polar dielectric material such as SrTiO3/BaTiO3 or MgO/BaTiO3. The proposed geometry of a FTJ does not require different electrodes [2], as a result of the structural asymmetry produced by the dielectric layer. Due to the change in the electrostatic potential with polarization reversal the non-polar dielectric barrier acts as a switch that changes its barrier height from a low to high value resulting in a dramatic change in the transmission across the FTJ. The predicted values of TER are giant and indicate that the resistance of the FTJ can be changed by many orders in magnitude at the coercive electric field of ferroelectric. This effect may be relevant to recent experimental results showing that the resistance of a FTJ can be changed by many orders of magnitude at the coercive electric field of the ferroelectric barrier [6,7]. Our work demonstrate an efficient method of enhancing TER and suggests that depositing a dielectric layer in a controllable way may provide a route to tailor TER which may be practical for device applications of FTJs.1. E. Y. Tsymbal and H. Kohlstedt, Science 313, 181 (2006).2. M. Y. Zhuravlev, R. F. Sabirianov, S. S. Jaswal, and E. Y. Tsymbal, Phys. Rev. Lett. 94, 246802 (2005).3. H. Kohlstedt, N. A. Pertsev, J. Rodríguez Contreras, and R. Waser, Phys. Rev. B 72, 125341 (2005).4. J. P. Velev, C.-G. Duan, K. D. Belashchenko, S. S. Jaswal, and E. Y. Tsymbal, Phys. Rev. Lett. 98, 137201 (2007).5. J. P. Velev, C.-G. Duan, J. D. Burton, A. Smogunov, M. K. Niranjan, E. Tosatti, S. S. Jaswal, and E. Y. Tsymbal, Nano Letters 9, 427 (2009).6. V. Garcia, S. Fusil, K. Bouzehouane, S. Enouz-Vedrenne, N. D. Mathur, A. Barthélémy, and M. Bibes, Nature, doi:10.1038/nature08128 (2009)7. A. Gruverman, D. Wu, H. Lu, Y. Wang, H. W. Jang, C. M. Folkman, M. Ye. Zhuravlev, D. Felker, M. Rzchowski, C.-B. Eom, and E. Y. Tsymbal, submitted paper.
Symposium Organizers
Alexei Gruverman University of Nebraska-Lincoln
Craig J. Fennie Cornell University
Iwao Kunishima Toshiba Corporation
Beatriz Noheda University of Groningen
Tae Won Noh Seoul National University
F7: Strain and Epitaxial Stabilization
Session Chairs
Chang-Beom Eom
Carlos Vaz
Wednesday AM, December 02, 2009
Grand Ballroom (Sheraton)
9:00 AM - **F7.1
Vertical Nanocomposites for Multiferroics and Enhanced Single Phase Functionality.
Judith Macmanus Driscoll 1 , Arnaud Fouchet 1 , Emily Weal 1 , Haiyan Wang 2 , Hao Yang 3 , Zhenxing Bi 2 , Quanxi Jia 3
1 Department of Materials Science and Metallurgy, University of Cambridge, Cambridge United Kingdom, 2 Department of Electrical Engineering, Texas A and M , College Station, Texas, United States, 3 MST-STC, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractTwo-phase nanocomposite heteroepitaxial films with vertical microstructures hold great promise for various (multi)functional electronic device applications. With the aim of creating addressable arrays, it is necessary to form spontaneously ordered structures over large areas. We show spontaneously ordered phase assemblies and find that these structures form concomitantly with two-dimensional vertical strain control, i.e. strain in the two phases is controlled along the vertical interface between them rather than being influenced by the substrate. A range of systems are explored and both novel multifunctionality and enhanced functionality are demonstrated.
9:30 AM - **F7.2
Strain Effects in Multiferroic BiFeO3 Re-visited.
Claude Ederer 0
0 School of Physics, Trinity College Dublin, Dublin, Co. Dublin, Ireland
Show AbstractBiFeO3 (BFO) is a very rare example of a material that exhibits both magnetic and ferroelectric order above room temperature, and is therefore a prime candidate for device applications based on multiferroic materials. BFO is often prepared in the form of epitaxial thin films and is thus subject to strain, induced by the lattice mismatch between BFO and the substrate material. Such strain can alter the properties of BFO compared to unstrained bulk single crystals and can in principle induce both structural and magnetic phase changes.In this talk I will give an overview over strain-induced changes in the crystal structure, ferroelectric polarization, and magnetic properties of BFO, obtained from first principles calculations using density functional theory. Calculations were performed for the unstrained bulk system as well as for epitaxially strained BFO corresponding to both (111) and (001) orientation of the substrate. The calculations corresponding to the commonly used (001) substrate-orientation indicate that moderate strain values of 1-2% give rise to only small to moderate changes in the properties of BFO, whereas for a large compressive strain around 4.5% a strain-induced iso-symmetric phase transition accompanied by a large increase in c/a ratio occurs. This is consistent with recent experimental observations of giant c/a ratio for BFO films grown on (001) LaAlO3 and YAlO3. (This work is done in collaboration with A. J. Hatt and N. A. Spaldin, University of California, Santa Barbara.)
10:00 AM - F7.3
A Strain-Driven Morphotropic Phase Boundary in BiFeO3.
R. Zeches 1 , M. Rossell 2 , J. Zhang 1 , A. Hatt 3 , C. Yang 4 , A. Kumar 5 , A. Melville 5 6 , J. Ihlefeld 5 6 , R. Erni 2 , C. Ederer 7 , V. Gopalan 5 , D. Schlom 6 , N. Spaldin 3 , L. Martin 8 , R. Ramesh 1 4 8
1 Department of Materials Science and Engineering, University of California, Berkeley, Berkeley, California, United States, 2 National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 3 Materials Department, University of California, Santa Barbara, Santa Barbara, California, United States, 4 Department of Physics, University of California, Berkeley, Berkeley, California, United States, 5 Department of Materials Science and Engineering, Pennsylvania State University, State College, Pennsylvania, United States, 6 Department of Materials Science and Engineering, Cornell University, Ithaca, New York, United States, 7 School of Physics, Trinity College Dublin, Dublin Ireland, 8 Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractWe report the coexistence of two structural phases, with an interface that is reminiscent of a classic morphotropic phase boundary, in strained single component BiFeO3 films. Epitaxial films grown on LaAlO3 and YAlO3 substrates exhibit a large tetragonal distortion (c/a ~ 1.26). As film thickness is increased, atomic force microscopy, second harmonic generation, and transmission electron microscopy reveal that this distorted tetragonal-like phase coexists with a highly distorted rhombohedral-like phase. This two-phase coexistence is consistent with first-principles density functional theory calculations. Electric field dependent atomic force microscopy studies show that the distorted tetragonal-like phase can be reversibly converted into the distorted rhombohedral-like phase, reminiscent of a classical morphotropic phase boundary in the related lead-based systems; this is accompanied by significant displacements of the surface (~1.2-2.4 nm / 100 nm of film thickness), which makes this new lead-free system of significant interest for probe-based data storage and actuator applications.
10:15 AM - F7.4
Non-linear Optical Probing of BaTiO3/SrTiO3 Superlattices and Their Enhanced Electro-optic and Piezoelectric Coefficients.
Eftihia Vlahos 1 , Che Lee 1 , Pingping Wu 1 , Sava Denev 1 , Chung Bark 2 , Ho Jang 2 , Chad Folkman 2 , Seung Baek 2 , Jae Park 2 , Michael Biegalski 3 , Darrell Schlom 4 , Chang Eom 2 , Long Chen 1 , Venkatraman Gopalan 1
1 Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania, United States, 2 Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States, 3 , Oak Ridge National Lab, Oak Ridge, Tennessee, United States, 4 Materials Science and Engineering, Cornell University, Ithaca, New York, United States
Show AbstractLayered superlattices are a very interesting class of artificial materials because they exhibit properties very different from their parent constituents. Theoretical phase-field simulations predict that certain types of superlattices consisting of alternating (BaTiO3)n/(SrTiO3)n layers have novel vortex domain wall configurations which give rise to exceptionally high polarization tunability combined with negligible polarization hysteresis. This enhances all the related odd-ranked polar properties such as electro-optic coefficients, and piezoelectric coefficients. Optical second harmonic generation (SHG) was used to probe the phase and transition temperatures of multilayer (BaTiO3)m/(SrTiO3)n superlattices, as a function of epitaxial strain, as well as their electro-optic coefficients. These results are in excellent agreement with theoretical predictions, as well as the temperature-strain phase diagram obtained experimentally from Raman studies. The ferroelectric, in-plane SHG signal, from the strained BaTiO3 layers reveals an mm2 point group symmetry, whereas the point group symmetry of the strained SrTiO3 layers, was determined to be 4mm. The piezoelectric and electro-optic coefficients of a series of superlattices are measured as a function of temperature from 300K to 5K that show significant enhancement of polar tensor properties over comparable mixed alloy phases.
11:00 AM - F7.5
Strain-induced Ferroelectricity in Simple Rocksalt Binary Oxides.
Eric Bousquet 1 2 , Nicola Spaldin 2 , Philippe Ghosez 1
1 Physics, LIEGE UNIVERSITY, Sart Tilman Belgium, 2 Materials Department, University of California, Santa Barbara, California, United States
Show AbstractRock salt binary AO oxides form an important family of compounds which was intensively studied, both experimentally and theoretically. In comparison to multifunctional ferroelectric perovskite oxides, their practical applications remain however limited and the emergence of ferroelectricity and related functional properties in simple binary oxides seems so unlikely that it was never previously considered. Here, we first show from first-principles density functional calculations that ferroelectricity can be easily induced in simple alkaline earth binary oxides such as BaO using appropriate epitaxial strains. We point out that the functional properties (polarization, dielectric constant and piezoelectric response) of such strained binary oxides are comparable in magnitude to those of typical ferroelectric perovskite oxides, so making them of direct interest for applications. Going further, we also show the possibility to induce ferroelectricity under epitaxial strain in ferromagnetic rock salt binary oxides like EuO, and so to make it multiferroic. Interestingly, the epitaxial strain is expected to increase the ferromagnetic Curie temperature together with inducing ferroelectricity suggesting a new route to achieve multiferroism at high temperature by combining ferroelectric and magnetic properties in very simple structures.
11:15 AM - F7.6
Evidence of Ferroelectricity Induced by Epitaxial Strain in Calcium Titanate Thin Films Grown by Molecular-beam Epitaxy.
Charles Brooks 1 2 , Eftihia Vlahos 1 , Michael Biegalski 3 , Nikolas Podraza 1 , Carl-Johan Eklund 4 , Craig Fennie 5 , Karin Rabe 4 , Venkatraman Gopalan 1 , Darrell Schlom 2
1 Materials Science and Engineering, Penn State University, University Park, Pennsylvania, United States, 2 Materials Science and Engineering, Cornell University, Ithaca, New York, United States, 3 Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 4 Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey, United States, 5 School of Applied and Engineering Physics, Cornell University, Ithaca, New York, United States
Show AbstractCaTiO3 has been predicted by first principles to have strain-induced ferroelectricity. With sufficient tensile strain the development of a polar instability is predicted to occur with polarization along a <110> pseudocubic direction relative to the primitive perovskite lattice vectors [1]. In accordance with these predictions, we report evidence of a ferroelectric transition in strained (100) CaTiO3 films grown by molecular-beam epitaxy (MBE). When deposited with LSAT (LaAlO3)0.3-(SrAl1/2Ta1/2O3)0.7 as the substrate, corresponding to an epitaxially-induced tensile strain of 1.3%, a 20 nm film of CaTiO3 exhibits ferroelectric characteristics in second harmonic generation (SHG) and in dielectric measurements. By x-ray diffraction, this 20 nm CaTiO3 on LSAT appears fully commensurate and has a rocking curve full-width at half max of 9 arc seconds. Both capacitance vs. temperature and SHG intensity vs. temperature results agree that the paraelectric-to-ferroelectric transition occurs around 150 K. At 20 K there is a remanent polarization of ~5µC/cm2. CaTiO3 on LSAT exhibits relaxor behavior including a frequency dispersion of the dielectric constant below the transition temperature and a slight increase in the dielectric constant vs. temperature peak with measurement frequency. SHG also confirms the predicted direction of polarization being parallel to the psuedocubic perovskite <110> direction. [1] C.-J. Eklund, C.J. Fennie, and K.M. Rabe, Phys. Rev. B 79, 220101(R) (2009)
11:30 AM - F7.7
Novel Ferroelectrics by Growth on Pseudocubic (111) Oriented Substrates.
Jeroen Blok 1 , Xin Wan 1 , Guus Rijnders 1 , Dave HA Blank 1
1 , University of Twente, Enschede Netherlands
Show AbstractA lot of research has been done on the effects of strain and symmetry on the properties of epitaxial ferroelectric perovskites (ABO3). However in most cases the systems that were studied were grown on (001) oriented substrates. Growing ferroelectrics in the (111) direction allows us to apply strain in a different way and if you grow [1:1] superlattices of two different materials it results in films where the neighbouring atoms on both A-site and B-site are always different. These materials have also been named double perovskites. We fabricated superlattices of two ferroelectric materials, by growing a [1:1] superlattice in the 111 direction. The unit cell of our ferroelectric is doubled, thereby the symmetry is altered. This allows the atoms to displace in more directions than in the simple unit cell without breaking symmetry. Therefore purely from a symmetry point of view the material has more freedom to choose it's direction of polarization. To fabricate these 111 oriented [1:1] superlattices the first objective is to achieve controlled growth on a (111) surface. We achieved (111) growth on both (111) LaAlO3 substrates and (111) SrTiO3 substrates, using the help of an appropriate buffer layer. In the case of LaAlO3 we use a thin layer of LaAlO3 and in the case of SrTiO3 we use a thin layer of SrRuO3 (<10 nm). On these buffered substrates we managed to grow CaTiO3, SrMnO3, BaTiO3, PbTiO3 and BiFeO3. All these materials are either ferroelectric or have been predicted to be ferroelectric under certain strain states. Using strain matching (that is selecting materials with equal, but opposite strain), we managed to keep the surface of the superlattice atomically smooth even after the growth of 100 monolayers. We will show this for the growth of a CaTiO3 - SrMnO3 superlattice on a (111) LaAlO3 substrate. We have used X-ray diffraction to show that the superlattice is fully strained to the (111) LaAlO3 substrate and to determine the unit cell of the superlattice. In this contribution we will focus on the growth and structural properties of the superlattices, as well as the resulting properties
11:45 AM - F7.8
Epitaxial BaTiO3 on Si and Ge.
James Reiner 1 , Fred Walker 1 , Charles Ahn 1
1 Applied Physics, Yale University, New Haven, Connecticut, United States
Show AbstractThe integration of crystalline oxides and semiconductors, which is relevant for both technological applications and fundamental scientific inquiries, has been made possible by the development of techniques that allow crystalline SrTiO3 to be grown on the silicon (001) surface. This integration allows the wide range of behavior exhibited by crystalline oxides to be combined with the technological advantages silicon exhibits over single crystal complex oxide substrates. We present results for the growth and characterization of epitaxial ferroelectric BaTiO3 films grown both on silicon using an ultra-thin SrTiO3 buffer layer and grown directly on germanium. The most successful approach to realizing these epitaxial oxide-silicon (001) heterostructures requires manipulating substrate temperature and oxygen pressure on a layer-by-layer basis during the deposition of the metal oxide layers. We recently made progress in understanding in detail the different atomic structures formed at various stages in this deposition process. We apply this knowledge to optimize the crystalline quality of the BaTiO3 and SrTiO3 in the oxide-silicon heterostructure for use in applications such as electro-optic modulators.
12:00 PM - F7.9
Tunable Microwave Dielectric Properties of Ba0.6Sr0.4TiO3 Thin Films.
Hui Du 1 , Lisa Alldredge 2 , Steve Perini 3 , Michael Lanagan 3 , Steven Kirchoefer 2 , Marek Skowronski 1 , Paul Salvador 1
1 Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States, 2 , Naval Research Laboratory, Washington, District of Columbia, United States, 3 Materials Research Institute, Pennsylvania State University, University Park, Pennsylvania, United States
Show AbstractThough single crystalline and polycrystalline Ba1-xSrxTiO3 (BST) exhibit high dielectric constants (>7,000), high tunabilities (>80%), and low dielectric losses (<2%), BST films exhibit strongly deteriorated properties with respect to those bulk values. In this work, we demonstrate the importance of dislocations and mismatch strains on the dielectric properties of BST thin films, using both experimental and theoretical approaches. Ba0.6Sr0.4TiO3 films were deposited using pulsed laser deposition on substrates having both different crystallographic qualities and different lattice mismatches to generate films having different dislocation concentrations and in-plane strain states. To ensure that dislocation contents and strain were well controlled, we studied the growth, crystalline quality, and relaxation processes for BST films. Films grew in an epitaxial 2D layer-by-layer growth mode and the films’ surface steps were similar to the original substrate steps. The highest quality films were grown on well-matched, high-quality substrates of GdScO3 and DyScO3. Unrelaxed films were coherently strained and exhibited similar quality to the substrate used; for example on GdScO3 substrates, the BST(002) rocking curve was only 23 arc seconds wide (very close to the 20 arc second value for the substrate). The temperature dependence of microwave dielectric properties— including dielectric constant, tunability, and loss— were measured in the GHz frequency range using interdigitated capacitor structures. Bulk-like dielectric properties were observed for strained Ba0.6Sr0.4TiO3 films grown on GdScO3(110), including a sharp peak at the Curie temperature in the dielectric constant. Though Ba0.6Sr0.4TiO3 films grown on GdScO3(110), including a sharp peak at the Curie temperature films grown on DyScO3(110) had similar crystalline quality, they exhibited much different dielectric properties, similar to BST films of much worse crystalline quality. Simulations were used to compare the experimentally determined properties for the highest quality films to those expected from Landau-Devonshire theory. The importance of both homogeneous strain, from lattice and thermal-expansion-coefficient mismatches, and inhomogeneous strains, associated with threading dislocations, will be emphasized.
12:15 PM - F7.10
The Effect of Biaxial Strain on the Ferroelectric Transition of SrTiO3.
Michael Biegalski 1 , Charles Brooks 2 , Susan Trolier-McKinstry 2 , Hans Christen 1 , Darrell Schlom 3
1 Center for nanophase materials science, Oak Ridge National Lab, Oak Ridge, Tennessee, United States, 2 Materials Science, Pennsylvania State University, University Park, Pennsylvania, United States, 3 Materials Science and Engineering, Cornell University, Ithica, New York, United States
Show AbstractUsing epitaxy and the misfit strain imposed by an underlying substrate, SrTiO3 thin films have been made ferroelectric near room temperature.1 Although SrTiO3 is normally not ferroelectric at any temperature, predictions based on thermodynamic analysis imply that a biaxial strain of order 1% will shift its paraelectric-to-ferroelectric transition temperature to the vicinity of room temperature.2 An unexpected surprise is that the strained SrTiO3 films exhibit several attributes that are consistent with relaxor ferroelectricity, including a frequency dependence of their dielectric constant.3 This has obscured the true effects of strain on the ferroelectric transition and it has become difficult to distinguish the effects of strain from effects of the relaxor nature of the ferroelectricity. In order to determine the effects of strain several films with different strain states were compared. Fully commensurate films of SrTiO3 were grown on four rare earth scandates, DyScO3, TbScO3, GdScO3, and EuScO3 to give strain states of 0.9%, 1.3%, 1.6% and 1.8% tensile biaxial strain. These films are all 20 nm thick and are below the critical thickness and these strained SrTiO3 films have better structural perfection (narrower rocking curve widths) than SrTiO3 single crystals. The effects of strain on the ferroelectric properties were determined by measuring the polarization-electric field hysteresis loops and dielectric permittivity as a function of temperature. The Tmax and corresponding onset of ferroelectric hysteresis loops for the films were found to range from 260 K for lowest strain state and increases with increasing strain to near 330 K for higher strain levels. The observed transition for each of these strain states compare well with thermodynamic predictions of the ferroelectric state that do not incorporate relaxor ferroelectric behavior. This clearly shows that the strain is the dominant mechanism for modifying the ferroelectric state in SrTiO3.Research sponsored by the Division of Scientific User Facilities, US Department of Energy.1 J.H. Haeni, P. Irvin, W. Chang, R. Uecker, P. Reiche, Y.L. Li, S. Choudhury, W. Tian, M.E. Hawley, B. Craigo, A.K. Tagantsev, X.Q. Pan, S.K. Streiffer, L.Q. Chen, S.W. Kirchoefer, J. Levy, and D.G. Schlom, Nature 430, 758 (2004).2. Y.L. Li, S. Choudhury, M.D. Biegalski, J.H. Haeni, A. Vasudevarao, A. Sharan, H. Z. Ma, J. Levy, V. Gopalan, S. Trolier-McKinstry, D. G. Schlom, Q. X. Jia, and L. Q. Chen Phys. Rev. B. 73, 184112 (2006).3. M. D. Biegalski, Y. Jia, V. Sherman,S. K. Streiffer, D. G. Schlom, and S. Trolier-McKinstry Appl. Phys. Lett. 88, 192907 (2006).
F8: Domains
Session Chairs
Byron Huey
Petro Maksymovych
Wednesday PM, December 02, 2009
Grand Ballroom (Sheraton)
2:30 PM - **F8.1
Phase-field Modeling of Ferroelectric Domain Switching.
Long-Qing Chen 1
1 , Penn State University, University Park, Pennsylvania, United States
Show AbstractThis presentation will discuss the phase-field method of ferroelectric switching in bulk single crystals and thin films as well as polycrystalline ceramics. In this method, ferroelectric switching is modeled by evolving the three-dimensional inhomogeneous polarization distribution under an applied electric field. It takes into account not only the actual domain structures but also the inhomogeneous electric and stress field distributions. Switching under both uniform field, simulating switching using large-area electrodes, and non-uniform field, simulating domain nucleation under a piezoresponse force microscopy (PFM), will be discussed. A number of examples will be presented, including switching of single-crystal and polycrystalline PZT, BFO, and BTO/STO superlattices under a uniform field, as well as local domain nucleation at defect-free surfaces and in the vicinity of ferroelastic twin boundaries and localized defects in PZT and BiFeO3 under PFM. It is shown that there are significant differences between local and large-area switching. The simulation results are compared to those obtained in actual switching measurements. The results to be presented result from collaborations with a number of experimental groups including S. K. Kalinin at Oak Ridge, C. B. Eom at University of Wisconsin, V. Gopalan at Penn State, D. G. Schlom at Cornell, R. Ramesh at UC Berkeley, X. Q. Pan at University of Michigan, D. Tenne at Boise State, X. X. Xi at Penn State, and Q. X. Jia at Los Alamos
3:00 PM - F8.2
Domain Control of (001) BiFeO3 Thin Films.
Christopher Nelson 1 , Yi Zhang 1 , Chad Folkman 2 , A. Melville 3 , C. Adamo 3 , Darrell Schlom 3 , Chang Beom Eom 2 , Xiaoqing Pan 1
1 Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States, 2 Materials Science and Engineering, University of Wisconsin, Madison, Wisconsin, United States, 3 Materials Science and Engineering, Cornell University, Ithaca, New York, United States
Show AbstractThe domain structure of rhombohedral ferroelectric thin films such as BiFeO3 and PZT can be manipulated by the mechanical and electronic properties of their interfaces. In this work we examine the influence of film thickness and electronic boundary properties on (001) BiFeO3 thin films in a very small strain system (<-0.2%). Two series of BFO films were grown on atomically flat (110) TbScO3 substrates. The first was a thickness series of BFO films ranging from 50-400nm was grown by rf magnetron sputtering. The second series consisted of 20nm and 100nm BFO films grown by molecular beam epitaxy both directly on the TSO surface and with conductive 20nm LaxSr1-xMnO buffer layers. Transmission electron microscopy and X-ray reciprocal space mapping indicate that the BFO films have a domain pattern of only two of the four potential ferroelastic variants. This is in contrast to BiFeO3 films on cubic substrates which possess all four variants. Thus, the reduced symmetry or the very small in-plane anisotropy of the TbScO3 substrate lowers the nucleation energy for the two observed ferroelastic variants.In the thickness series made by rf sputtering all the BiFeO3 films were to adopt one of two patterns depending upon film thickness. The thinnest film of the series, 50 nm, formed a stripe domain pattern of vertical domain walls with a 109° rotation in polarization between domains. The thicker films ranging from 100 nm to 400 nm formed a stripe pattern orthogonal to the 50 nm case with inclined domain walls separating 71° domains. This change in domain pattern with thickness is attributed to the increase in the depolarization field with decreasing film thickness as neither interface is compensated. At small thicknesses the alternating out-of-plane polarization of the 109° domains is favored as it results in no depolarization field. For thicker films the lower energy 71° domains are favored.The BFO films grown directly on TbScO3 by MBE adopt a 109° domain pattern like that observed in the 50 nm film grown by rf sputtering. The same short-period 109° domain pattern was absent in the films grown on conducting LSMO buffer layers although a small number of vertical domain walls were still present. Since the free charges in the buffer layer will damp the depolarization field, this series again illustrates the presence of the 109° domain pattern only when the depolarization field is large.
3:15 PM - F8.3
Nanoscale X-ray Scattering Investigation of Local Domain Configuration in Epitaxial BiFeO3 Thin Film Nanostructures.
Jeffrey Klug 1 2 , Ramesh Nath 2 5 , Alexandra Imre 2 3 , Martin Holt 3 , Volker Rose 4 , Seungbum Hong 2 , Ram Katiyar 5 , Michael Bedzyk 1 2 6 , Orlando Auciello 1 2
1 Department of Physics and Astronomy, Northwestern University, Evanston, Illinois, United States, 2 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States, 5 Department of Physics and Institute for Functional Nanomaterials, University of Puerto Rico, San Juan, Puerto Rico, United States, 3 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, United States, 4 Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois, United States, 6 Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois, United States
Show AbstractX-ray nanodiffraction has been used to study the local structure of epitaxial BiFeO3 (BFO) thin film nanostructures. A two-step process combining electron beam lithography and focused-ion beam (FIB) lithography with a removable metal mask was employed to fabricate capacitors with negligible ion beam damage. Nanostructures with lateral dimensions ranging from 1000 nm to 200 nm were produced from a 35 nm thick BFO film grown by magnetron sputter-deposition on a SrRuO3 -coated SrTiO3 (001) substrate. Capacitors with square and rectangular shapes were fabricated with planar orientations from 0° (orientation along one substrate edge) to 15°, 30°, 45° and 90° orientation with respect to the initial 0° orientation. Circular capacitors were fabricated to determine round edge effects vs. straight edge and corner effects in square and rectangular nanocapacitors on film strain and polarization domain structure. Utilizing a sub- 50 nm focused x-ray beam spot at the Hard X-ray Nanoprobe beamline at the Advanced Photon Source, diffraction measurements were made on nanostructures with varied size, shape (e.g. symmetry, aspect ratio) and orientation (relative to the film in-plane crystallographic axes) to map the local strain and crystal orientation. Differences between the patterned nanostructures and blanket film region will be discussed, and diffraction results will be presented alongside analysis of Piezoresponse Force Microscopy (PFM) measurements to examine the relation between local strain and lattice rotation and the ferroelectric domain structure of laterally confined nanostructures.Work in the Materials Science Division and use of the Advanced Photon Source and the Center for Nanoscale Materials were supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
3:30 PM - F8.4
Global and Local Measurements of Domain Wall Mobility in Polycrystalline Ferroelectric Thin Films.
Patamas Bintachitt 1 , Susan Trolier-McKinstry 1 , Stephen Jesse 2 , Katyayani Seal 2 , Sergei Kalinin 2
1 Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania, United States, 2 The Center for Nanophase Materials Science, Oak Ridge National Laboratory, University Park, Tennessee, United States
Show AbstractThe lead zirconate titanate (PZT) films that are most widely utilized as piezoelectric layers in MEMS are polycrystalline, with random orientation of the grains. The resulting transverse piezoelectric coefficient, e31,f, is approximately -6 to -7 C/m2 for a PZT 52/48. Higher piezoelectric coefficients, e31,f of -14 C/m2 and -10.0 C/m2 were achieved for PZT thin films of 1.0 μm and 0. 24 μm thickness, respectively. The local and global domain wall contributions in both {001}-textured and random PZT films were studied by piezoelectric nonlinearity and global dielectric nonlinearity. Band Excitation Piezoelectric Force Microscopy (BE-PFM) was shown to enable quantitative measurements of the local piezoelectric nonlinearity. It was found that films over the thickness range from 0.2 to 4.4 microns showed Rayleigh-like behavior. 4 μm thick films were nearly uniform in their Rayleigh coefficient, suggesting that any heterogeneities in the response developed at lateral length scales below the resolution of the PFM measurement. In contrast, thinner films showed significantly more patchiness in their response, so that fluctuations in behavior developed at a lateral length scale on the order of 0.6 to 2.5 micron. These variations did not appear to be correlated directly with the surface topology. The ability to detect lateral inhomogeneity in the nonlinearity of thinner films is likely to be a function of the volume probed in the measurement. Finally, based on a comparison of the averaged local and global Rayleigh coefficient ratios, it is hypothesized that the same population of domain wall contributes to the dielectric and piezoelectric responses.
4:15 PM - **F8.5
Modeling Ferroelectric Domain Wall Structure, Energetics, and Dynamics.
Tingting Qi 1 , Jacob Colbert 1 , I-Wei Chen 2 , Andrew Rappe 1 2
1 Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania, United States, 2 Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States
Show AbstractIn this talk, the properties of ferroelectric domain walls areexplored with multi-scale modeling. First-principles calculations areperformed to reveal atomic and electronic properties at the interfacecore. Molecular dynamics with a first-principles-derived bond-valencemodel will provide insight into domain formation, as well as thenucleation and growth model of domain wall motion. Results will beinterpreted and extended with Monte Carlo and continuum LandauGinzburg Devonshire ferroelectric formulations, to associate atomisticfeatures with the spatial profile of the order parameter. Comparisonsbetween walls in different materials and different domain wallorientations will be made.
4:45 PM - F8.6
Transmission Electron Microscopy Investigation of Multiferroic TbMnO3Thin Films.
Sriram Venkatesan 1 , Bart Kooi 1 , Christophe Daumont 1 , Beatriz Noheda 1 , Jeff De Hosson 1
1 , Zernike Institute for Advanced Materials,University of Groningen, Groningen Netherlands
Show AbstractPerovskite manganites with a strong coupling between spontaneous electrical and magnetic polarizations are a topic of severe current interest because of their fundamental scientific importance and potential technological applications in magnetoelectric (ME)-optic devices.The orthorhombic TbMnO3 (TMO) is receiving much attention because of its coupling of magnetic spins and electrical degrees of freedom resulting in a strong ME effect.In this work, TMO films were laser ablated from stoichiometric targets on (001) oriented SrTiO3 substrates. This film-substrate combination has been investigated scarcely. The films in orthorhombic form are effectively under a compressive strain. Our main focus here is to study, using Transmission Electron Microscopy (TEM), the domain structures and the domain walls present in TMO films as a function of film thickness, growth condition and indirectly as a function of in-plane strain. A series of films, with thickness in-between 2 and 140 nm, were grown at 0.25 and 0.9 mbar oxygen partial pressures. Different thicknesses of the films exhibit different domain structures. The microstructural analyses of the films grown at different thickness explain the growth mechanism of the TMO on STO. Based on our TEM imaging and diffraction studies we infer that TMO always grows with its c-axis perpendicular to the STO(001) surface. The domain structure of the film gradually changes when viewed in plan-view from two (nearly perpendicular) sets of twins with needle like shape to a uniform near circular shape with increasing thickness. This shape change reflects the change in film-substrate orientation relationship, where for thinner films [110] and [1-10] of the orthorhombic film are parallel to [100] and [010] of the cubic substrate and where for the thicker films [100] and [010] of the film become parallel to [110] and [1-10] of the substrate. So, below about 50 nm thickness the four domain variants giving the two sets of twins are: (i) [110]o//[100]c (ii) [-110]o//[100]c (iii) [110]o//[010]c and (iv) [-110]o//[010]c. For higher thicknesses only two orientation relations remain: (i) [100]o//[110]c = [010]o//[1-10]c (ii) [100]o//[1-10]c = [010]o//[110]c.The results show that the films grown at higher oxygen partial pressure (0.9mbar) exhibit strain relaxation at lower thickness (50nm) when compared to the films grown at lower pressure (0.25mbar). This difference is attributed to a higher concentration of oxygen vacancies at lower oxygen partial pressure and therefore a reduced strain. Strain relaxation in the film occurs by two mechanisms: 1. Misfit dislocation formation at the substrate-film interface and 2. Formation of columnar structures with increasing relaxation at the column boundaries with increasing thickness. At 0.9mbar the first mechanism dominates, whereas at 0.25mbar the second one occurs.
5:00 PM - F8.7
Coherent X-ray Diffraction from Polarized Nanoscale Domains in PbTiO3 Thin Films Grown on DyScO3.
Stephan Hruszkewycz 1 , Matthew Highland 1 , Ross Harder 2 , Alexandra Imre 3 , Paul Fuoss 1
1 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States, 2 X-ray Science Division, Argonne National Laboratory, Argonne, Illinois, United States, 3 Center for Nanomaterials, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractCoherent x-ray diffraction imaging (CDI) is an emerging lensless imaging technique in which the shape and lattice strain of sub-micron domains (or crystals) can be recovered in three dimensions at potentially sub-nanometer resolution. CDI involves measuring a three-dimensional volume of reciprocal space containing a Bragg diffraction peak, then inverting the diffraction pattern using iterative phasing algorithms to create the corresponding three-dimensional density and phase images of the diffracting volume. This technique holds intriguing promise for exploring the complex pattern of crystallographic orientations and strains that occur in nanostructured ferroelectric films. Although these issues have been studied for some time, they are still relatively poorly understood in local as opposed to average behavior, and, because of electromechanical coupling, have a strong impact on ferroelectric performance. In particular, CDI can non-destructively determine complex domain shapes and strain distributions using an uncharged probe. We have performed parallel beam hard x-ray coherent diffraction experiments on 100 nm thick PbTiO3 thin films grown on DyScO3 pseudo-cubic <100> substrates. At room temperature, the polarized tetragonal PbTiO3 film adopts a fine ~100nm scale domain microstructure of c and a axis-normal domains. To accommodate the current instrument stability, we used focused ion beam milling to isolate 0.5 to 1.5 micron sized regions of PbTiO3 film, each of which contain large numbers of c and a domains. At the Advanced Photon Source beam line 34ID-C, we used a coherent x-ray beam to fully illuminate a single region and measured three-dimensional diffraction patterns from the four different orientations of both c and a domains. Interference from the edges of individual domains as well as from the network of similarly oriented domains combine to form a complex, densely speckled diffraction pattern. Using carefully chosen algorithm constraints and experimental data corrections, we are using Fienup-like phasing algorithms to invert these diffraction data into three-dimensional images of c and a domains contained within the PbTiO3 thin film. These density and phase maps will be a powerful tool to help illuminate the morphology and strain states of these domains at the DyScO3 interface and open the door for in-situ switching imaging studies, investigating dynamic domain evolution.
5:15 PM - F8.8
Novel Large Piezoelectric Response in The Tetragonal Pb(Ti, Zr)O3 Thick Films by 90° Domain Wall Motion.
Mitsumasa Nakajima 1 , Hiroshi Nakaki 1 , Tomoaki Yamada 1 , Ken Nishida 2 , Takashi Yamamoto 2 , Minoru Osada 3 , Hiroshi Funakubo 1
1 Department of Innovative and Engineered Materials, Tokyo Institute of Technology, Yokohama, Kanagawa, Japan, 2 Department of Communications Engineering, National Defense Academy of Japan, Yokosuka-shi, Kanagawa, Japan, 3 International Center for Materials Nanoarchitectonics, National Institute for Materials Science (NIMS), Tsukuba, Ibaraki, Japan
Show AbstractFerroelectric lead zirconate titanate (Pb(Zr,Ti)O3, PZT) films are attractive for many applications, such as sensors and actuators in microelectrical-mechanical systems (MEMS) because of their high piezoelectric response. It was reported in bulk PZT systems that the motions of 90° domain walls under the electric field significantly enhance the piezoelectric response and they play a key role of large piezoelectric response [1]. However, in the case of thin film, the movement of 90° domain wall is more difficult than that in bulk PZT due to the clamping from the substrates, so that the realization of high piezoelectricity is not achieved [2]. Nevertheless, we note that optimization of the volume fraction of (001) orientation can be very efective to best utilize the contribution from 90° domain wall motion in the (001)/(100) – oriented film[3]. In this study, we report on a piezoelectric responses in the tetragonal PZT thick films in which c/a ratio and the volume fraction of (001) orientation (Vc) were controlled.Epitaxial Pb(Ti0.6Zr0.4)O3 films with a thickness of about 2 μm were grown on (100)cSrRuO3//(100)LaNiO3//(100)CaF2, (100)cSrRuO3//(100)SrTiO3, (100)cSrRuO3//(100)KTaO3 and (100)c SrRuO3//(100)LaNiO3//(100)YSZ//(100)Si substrates to conrol the Vc by MOCVD. The struatual characterizations were performed by X-ray diffraction (XRD) and Raman spectroscopy. Vc of these films was estimated to be 100, 50, 33 and 25 % respectively by XRD measurements using following equation; Vc=I001/(I100+I001). Piezoelectric response was measured using piezoelectric force microscopy (PFM). Crystal structure change under electric field was measured using Raman spectroscopy through the 10-nm thick Au top electrode.The piezoelectric constant (d33) of PZT films estimated from strain electric field (S-E) curve was 60 , 70, 300 and 390 pm/V, respectively. It was noted that the signinficant enhancement of the piezoelectric responce for the films with Vc = 25-35 %, which is around five times larger than PZT films with only 180° domain (Vc=100 %), 60 pm/V, grown on buffer layerd CaF2 substrates. From the careful analysis of Raman spectra under the electric field, it was found that observed large piezoelectric responses could be explained by the contribution of 90° domain wall motions. The reason of enhancement of piezoelectricity can be considered as increment of the density of 90° domain wall. The large piezoelectric response observed in the films with Vc = 25-35 % gives us chances to enhance the piezoresponse even in film form applicable to wide variety of applications.[1] Tsurumi et al, Jpn. J. Appl. Phys., 36 5970 (1997).[2] K. Lefki et al, Appl. Phys. Lett. 76 1764 (1994).[3] P. M. Chaplya et al, J. Appl. Phys. 90 5278 (2001)
5:30 PM - F8.9
Phase-field Simulation of Thickness Dependence on Domain Stabilities in Ferroelectric Thin Films.
Guang Sheng 1 , Jingxian Zhang 1 , Yulan Li 1 , Samrat Choudhury 1 , Quanxi Jia 2 , Zi-Kui Liu 1 , Long-Qing Chen 1
1 Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania, United States, 2 MPA-STC, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show Abstract It is well accepted that the domain/phase stability is controlled by both mechanical and electrical boundary conditions in ferroelectric thin films. There has been increased interest in understanding the size effect, i.e., the thickness dependence of domain stabilities and dielectric properties by experiment as well as theory. In this study, we employ the segregated strain model to evaluate the effective (real) misfit strain between thin film and substrate. A 3-d phase-field model was constructed to investigate the domain stability of (001) oriented epitaxial PbTiO3 thin films that takes into account both effective misfit strain as well as thickness induced depolarization field in the films. The c-type domain percentage as a function of film thickness from the phase-field simulations agrees very well with experimental measurement of PbTiO3 thin films grown on different substrates with a series of misfit strain and thickness. The corresponding “thickness-effective strain” domain stability diagram was constructed at different temperatures and it is expected that such diagrams will provide guidance for interpreting experimental measurements and observations as well as to the design of PbTiO3 films with specified thickness and domain structures.
5:45 PM - F8.10
Nanoporous Ferroelectric Thin Film Structures.
Paula Vilarinho 1 , Ru Zhong Hou 1 , Paula Ferreira 1 , Aiying Wu 1
1 Dep. of Ceramics and Glass Engineering, University of Aveiro, Aveiro Portugal
Show AbstractAfter the achievement of ferroelectrics in the bulk form, the design, synthesis and characterization of nanometric ferroelectrics structures are becoming particularly important, since “scaling of electronics” is still a key aspect for Semiconductor Industry as stated in 2008 International Technology Road Map for Semiconductors report [1]. Manipulating the morphology of ferroelectrics at nano-scale has both fundamental and practical meanings, to study the size effects and influence of free surface, as well as exploring novel features of ferroelectrics and applications. Nanoporous ferroelectrics can be seen as composites consisting of air (εr=1) and ferroelectric materials with very high relative dielectric constant εr. From the classic bulk materials approach, porosity is adverse being directly reflected in the lowering of εr. However it is known that porosity enhances piezoelectric figures of merit and modifies tunability under dc bias. Moreover nanoporosity should be regarded as a tool to engineer composite nanostructures.This study proves the concept that a low cost solution based process can be used to fabricate nanoporous lead titanate (PbTiO3) thin film structures. The films were deposited by dip-coating into lead titanate precursor solution containing poly (styrene-b-ethylene oxide) micelles. Calcination was performed to crystallize lead titanate and to remove the polymer resulting in porous structures. The 3-dimentional porous network provided the matrix for the further functionalization. A sol gel based process was then used to fabricate nanocomposite structures. The grain size and organization of the porous structure varied with experimental parameters such as precursor solution concentration, number of depositions and calcination time, among others. Atomic force microscopy provided 3-dimentional information about the nanoporous structure and square d33 loops were recorded during the piezo-response measurement on individual lead titanate grains in the porous structure. The relations between processing, nanostructure and properties are discussed for these nanocomposite thin films. References:[1]International Technology Roadmap for Semiconductors, 2008, http://www.itrs.net/Links/2008ITRS/Home2008.htm.
F9: Poster Session: Simulation and Modeling
Session Chairs
Thursday AM, December 03, 2009
Exhibit Hall D (Hynes)
9:00 PM - F9.1
Effective Energy of Perovskite Solid Solutions and Applications to Ferroelectric Phase Transitions.
Jeong Ho You 1 , K. Bhattacharya 1
1 , California Institute of Technology, Pasadena, California, United States
Show AbstractLead zirconate titanate (PbZr1-xTixO3 or PZT) solid solution has been studied intensively due to its interesting behaviors near morphotropic phase boundary (MPB). The temperature-independent MPB separates between the tetragonal phase in Ti-rich side and the rhombohedral phase in Zr-rich side at about x=0.48. Near MPB, high dielectric constants and high piezoelectric coefficients have been observed. Also, nanoscale domains are reported only near the MPB. First principles study of these disordered solid solutions is prohibitively expensive, while the empirical continuum type models do not contain sufficient detail to be predictive. A virtual crystal approximation (VCA) has been proposed that introduces a “virtual” atom with a potential averaged from parent compounds, however many of the core interactions are uniform in this approximation. In the present work, an effective energy is proposed without using the VCA. Detailed microscopic information is obtained from the density functional theory (DFT) calculations. Relative atomic displacement of Ti/Zr atom from its cubic position is defined as a key kinematic variable to describe ferroelectric phase transitions. Effective energy, which is a continuous functional form as a function of the key kinematic variable, is fitted from selective DFT calculations to represent the macroscopic energy landscape. Using the fitted effective energy, macroscopic phase transitions of PZT at various mole fractions have been studied using Monte Carlo simulations at a finite temperature. A sudden phase change between tetragonal and rhombohedral structures has been observed corresponding to MPB.
9:00 PM - F9.10
Extended System Molecular Dynamics Simulation of the Ferroelectric Materials: PT, PZ, and PZT.
Justin Haskins 1 , Tahir Cagin 1
1 Chemical Engineering, Texas A&M, College Station, Texas, United States
Show AbstractThe previously proposed polarizable charge equilibrium (PQEq) force field model [1] is parameterized for studying lead titanate (PT), lead zirconate (PZ), and their alloys: lead zirconate titanate (PZT). Several molecular dynamics (MD) simulations are performed to assess the degree of accuracy of the model. The phase transition temperatures, which are generally inaccurate in MD, are shown to be similar to experimental measurements. Also, the first-ever calculation of the ferroelectric hysteretic behavior with extended MD is shown to give a qualitatively correct comparison between PZ, PT, and PZT. The accuracy of the electronic properties in PQEq leads to direct application to a range of interesting problems such as enhanced properties of piezo- and ferro-electric nanostructures and the kinetics of domain walls in these materials.[1] Q. S. Zhang, T. Cagin, W. A. Goddard, III, Proc. Nat. Acad. Sci. USA, 103, 14695 (2006).
9:00 PM - F9.12
Vortex Polarization Instability in PbTiO3 Nanowires.
Ghanshyam Pilania 1 , Rampi Ramprasad 1
1 IMS, CMBE, University of Connecticut, Storrs, Connecticut, United States
Show AbstractThe possibility of circular, toroidal or vortex-like ordering (closure domains) of magnetic spin vectors have been considered by several including Landau, Lifshitz and Kittel, over the past 60 years. Recently, the presence of such vortex-like domains of electric polarization vectors has been anticipated in ferroelectric nanostructures based on phenomenological models of polarization and effective hamiltonian based simulations. These closure domains of electric polarization in nanostructures are of much scientific and technological interest because of their promise in making Tbyte/inch2 memory density a reality. However, a satisfactory understanding of the atomic-level origins and mechanisms that could result in such novel dielectric response and polarization states is unavailable at the present time.Here, for the first time using ab initio density functional theory (DFT) based computations, we show the existence of such a vortex polarization state in PbTiO3 (001) nanowires. Our computations involved relaxed and axially strained free-standing PbTiO3 (001) nanowires with varying sidewall terminations and diameters. While nanowires with their sidewalls terminated by PbO surfaces displayed purely axial polarization at all diameters, the TiO2-terminated nanowires, at a critical diameter of 16 Å, displayed a vortex polarization transverse to the nanowire axis corresponding to a toroidal moment directed purely along the nanowire axis. Moreover, we predict the existence of a novel stress-induced phase transition in the TiO2-terminated PbTiO3 nanowires. In the stress-free ground state, the nanowire displays a pure vortex polarization state with zero axial polarization. However, an axial tensile strain results in the progressive decrease of the the toroidal moment, with the disappearance of the vortex state at a critical strain of 3% accompanied by the abrupt appearance of an axial polarization. It thus appears that strain can be used to control the type of polarization ordering in such nanowires. To further confirm the vortex polarization instability in strain free nanowires, we carried out normal mode vibrational frequency analysis for the reference paraelectric TiO2-terminated nanowire. We found that the mode corresponding to the lowest imaginary frequency (the vortex “soft mode”) showed a clear vortex-like distortion. Charge density analysis indicated that the dominant interactions that mediate the vortex distortion are the covalent Pb-O interactions.
9:00 PM - F9.13
LaTiO3 and SmTiO3 Monolayers in SrTiO3 as a Two-Dimensional Electron Gas.
Christopher Nelson 1 , Yi Zhang 1 , Michael Katz 1 , Xiaoqing Pan 1 , Ho Jang 2 , Chad Folkman 2 , Seung Baek 2 , S. Lee 2 , Chang Beom Eom 2 , D. Su 3 , Y. Zhu 3 , D. Blom 4 , D. Felker 5 , M. Rzchowski 5 , Y. Wang 6 , M. Niranjan 6 , E. Tsymbal 6
1 Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States, 2 Materials Science and Engineering, University of Wisconsin, Madison, Wisconsin, United States, 3 Applied Science, Brookhaven National Laboratory, Upton, New York, United States, 4 EM Center, University of South Carolina, Columbia, South Carolina, United States, 5 Physics, University of Wisconsin, Madison, Wisconsin, United States, 6 Physics and Astronomy, University of Nebraska, Lincoln, Nebraska, United States
Show AbstractThe recent discovery of a two-dimensional conducting layer at the interface between the insulating perovskite oxides SrTiO3 and LaAlO3 was made possible by advances in atomic layer controlled growth that allowed creation of atomically-abrupt interfaces between novel complex oxide materials. It has been demonstrated that the carrier concentration can be altered with an electric field, and that the conducting layer can apparently be localized within a few nanometers of the interface, resulting in a two-dimensional electron gas (2DEG). In this work we examine atomic structure and electronic properties of two material systems in which single unit cells of the perovskites LaTiO3 and SmTiO3 were grown on (001) SrTiO3 substrates and capped by a 10 unit cell thick SrTiO3 overlayer by pulsed laser deposition. Although the bulk materials are insulators, the interfaces near the LaTiO3 and SmTiO3 layer are good conductors. High-angle annular dark field imaging using a spherical aberration (Cs) corrected atomic resolution scanning transmission electron microscope revealed that the thickness of LaTiO3 and SmTiO3 layers is between 1 and 3 unit cells and free of dislocations. The valence of the Ti atoms varies across the interface between LaTiO3 (or SmTiO3) and SrTiO3, determined by the electron energy-loss near edge structure of the Ti L2,3 core energy loss spectra. In the vicinity of the LaTiO3 and SmTiO3 layer, the Ti site deviates from the Ti4+ of bulk SrTiO3 toward Ti3+. The extra electron confined to the LaTiO3 and SmTiO3 layers is responsible for the measured metallic conductivity.
9:00 PM - F9.14
Phase-field Simulations of Domain Structures in Polycrystalline PZT Thin Films.
Benjamin Winchester 1 , Samrat Choudhury 2 , Long Qing Chen 1
1 Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania, United States, 2 Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States
Show AbstractWe studied the domain structures, polarization, and piezoelectric responses of polycrystalline PZT thin films using phase-field simulations. A polycrystalline grain structure was generated using a separate phase-field model for grain growth. We used the thermodynamic potential which was originally developed for bulk PZT ceramics, including strain, domain wall, electric, and Landau energy at room temperature. Based on the phase-field simulations, we will discuss the effects of grain size, orientation, and epitaxial substrate strain on the domain size, magnitude of polarization, and piezoelectric properties of PZT ferroelectric thin films near the morphotropic phase boundary.
9:00 PM - F9.15
Magnetoelectric Effect at the SrRuO3/BaTiO3 (001) Interface Mediated by the Polarization-dependent Exchange Splitting.
Manish Niranjan 1 , J. Burton 1 , J. Velev 2 , S. Jaswal 1 , E. Tsymbal 1
1 Dept. of Physics and Astronomy & Nebraska center for Materials and Nanoscience, University of Nebraska, Lincoln, 68588, Nebraska, United States, 2 Dept. of Physics, University of Puerto Rico, San Juan, 00931, Puerto Rico, United States
Show AbstractFerroelectric materials in combination with ferromagnets have emerged as structures in which strong magnetoelectric coupling may exist originating from unconventional physical mechanisms. Some recent theoretical studies deal with the magnetoelectric coupling occurring at the interfaces due to purely electronic mechanisms involving interface bonding [1,2] and charge screening [3,4]. Here we present a study of the magnetoelectric effect at the SrRuO3/BaTiO3(001) interface within the framework of density functional theory. This heterostructure is interesting since SrRuO3 is a weak ferromagnetic oxide metal and hence, when used as an electrode on BaTiO3, allows coupling between ferroelectric and ferromagnetic order parameters. Our calculations predict that the magnetization and exchange splitting of the spin-polarized band structure at the interface can be altered substantially by reversal of the ferroelectric polarization in the BaTiO3. This magnetoelectric effect originates from the spin-dependent screening of polarization charges at the SrRuO3/BaTiO3 interface, as was found previously for surfaces and interfaces not involving a ferroelectric component [3,4]. The new and important feature that follows from our calculations is the effect of ferroelectric polarization on the exchange splitting of the spin bands in SrRuO3. This phenomenon is consistent with the Stoner model for itinerant magnetism that explains the exchange splitting in terms of the density of states at the Fermi energy and the Stoner exchange parameter. The exchange-mediated mechanism for the interface magnetoelectric effect may be general for an itinerant ferromagnetic metal and a ferroelectric heterostructure. [1] C.-G. Duan, S. S. Jaswal, and E. Y. Tsymbal, Phys. Rev. Lett., 97, 047201 (2006).[2] M. K. Niranjan, J. P. Velev, C.-G. Duan, S. S. Jaswal E. Y. Tsymbal, Phys. Rev. B, 78, 104405 (2008).[3] J. M. Rondinelli, M. Stengel, and N. A. Spaldin, Nature Nanotechnology, 3, 46, (2008).[4] C.-G. Duan, J. P. Velev, R. F. Sabirianov, Z. Zhu, J. Chu, S. S. Jaswal, and E. Y. Tsymbal, Phys. Rev. Lett., 101, 137201 (2008).
9:00 PM - F9.16
Vibrational Properties of Ferroelectric β-Vinylidene Fluoride Polymers and Oligomers.
Rafal Korlacki 1 , Serge Nakhmanson 3 , J. Travis Johnson 1 , Stephen Ducharme 1 , Zhongxin Ge 2 , James Takacs 2
1 Department of Physics and Astronomy and Nebraska Center for Materials and Nanoscience, University of Nebraska-Lincoln, Lincoln, Nebraska, United States, 3 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States, 2 Department of Chemistry and Nebraska Center for Materials and Nanoscience, University of Nebraska-Lincoln, Lincoln, Nebraska, United States
Show AbstractLattice instabilities in ferroelectric materials are intimately linked to their structural and electroactive properties. The important consequences of the presence of these low-frequency modes on the material’s physical properties have been extensively studied for most prototypical perovskite oxides, but are lacking for many polymeric ferroelectrics.We applied a combined theoretical (plane-wave density functional theory [1]) and experimental (IR spectroscopy and spectroscopic ellipsometry) approach to study phonons and phonon dispersions for crystalline β-vinylidene fluoride polymers (β-PVDF) and oligomers. We have employed the most symmetric (space group Pmm2) structural model for β-PVDF as a starting point. Its conventional unit cell contains two 6-atom VDF monomers that are “polymerized” into two infinite chains by applying periodic boundary conditions along the chain axis. The cell was relaxed to small ionic forces and stresses, with resulting lattice constants being in excellent agreement with experiment. The obtained phonon dispersion curves computed for this structure appear to be unstable with lattice instabilities be-ing present at Y(0,1/2,0), S(1/2,1/2,0), and along the line connecting these two k-points. However, if the original unit cell is doubled in the chain (backbone) direction and the lowest-energy soft phonon at Y point (B1 symmetry at 32.7i cm-1) is frozen in, producing a slight dihedral distortion of VDF mono-mers along the chain, there are no instabilities present anywhere in the new Brillouin zone. This dihe-dral staggering should disorder well below room temperature. Such a softening transition has been ob-served at 160K from inelastic neutron scattering [2].The role of molecular and crystal interactions can be further explored in the case of vinylidene fluoride oligomers, which show similar ferroelectric properties to PVDF. Our recent studies of the vibrational modes through modeling and infrared ellipsometry indicate that this will be an interesting analog [3].This work was supported by the Department of Energy EPSCoR National Laboratory Partnership Program (DE-FG02-08ER46498) and the Nebraska Research Initiative.References[1] We used a DFT code Quantum Espresso (http://www.pwscf.org) and Vanderbilt ultrasoft pseudopotentials for the calculations[2] C. N. Borca, S. Adenwalla, J. Choi, P. T. Sprunger, S. Ducharme, L. Robertson, S. P. Palto, J. Liu, M. Poulsen, V. M. Fridkin, H. You, and P. A. Dowben, Phys. Rev. Lett. 83, 4562 (1999)[3] R. Korlacki, J. T. Johnson, J. Kim, S. Ducharme, D. W. Thompson, V. M. Fridkin, Z. Ge, and J. M. Takacs, J. Chem. Phys. 129, 064704 (2008)
9:00 PM - F9.17
Non-collinear Magnetization Density in Strained Mn-based Piezomagnets.
Pavel Lukashev 1 , Renat Sabirianov 1
1 Physics, University of Nebraska, Omaha, Omaha, Nebraska, United States
Show AbstractIn this work we present results of our calculations on systems with frustrated triangular magnetic structure (Mn-based antiperovskite compounds, Mn_{3}AN (A=Ga, Zn)) under bi-axial strain. Mn_{3}AN is non-magnetic in the ground state with the local magnetic moments (LMM) of Mn atoms forming a triangular curl in (111)-plane, but develops magnetization under external mechanical strain because of the change in the Mn LMMs both in magnitude and direction. The strain can be induced by forming a heterostructure with ferroelectric/piezoelectric material (magnetoelectric effect). The piezomagnetic effect is linear up to 2% of the strain. The commonly accepted approach to treat the spin dynamics for the excited states of magnetic materials is to apply quasispin approximation [1], according to which the magnetization density (MD) around each atom is taken constant within atomic sphere or polyhedron. We analyze MD distribution in (111)-plane of the unit cell as a function of the bi-axial strain and we show that MD in the Mn_{3}AN forms a domain structure around each atomic site but the density of this “spin cloud” has a more complex form than the uniform distribution of the rigid spin model, i.e. 3 Mn atoms in (111)-plane form more than 3 magnetic domains, with the shape and size of these domains being function of the strain. We show that both magnitude and orientation distribution of the spin density change under compressive and tensile strains, and the direction of the domains’ orientation directly correlated with the reversal of the strain, i.e. switching compressive to tensile strain (and vice versa) results in “reversal” of the domains. We present results of our analysis for the inter-atomic exchange interactions and the way they affect the domain structure. Finally, we analyze the appearance of the spin polarization (SP) in the system under strain and we discuss possible device applications of this effect.[1] S. H. Liu “Quasispin model of itinerant magnetism”, Phys. Rev. B. 13, 3962, 1976
9:00 PM - F9.18
Prediction of a Switchable Two-Dimensional Electron Gas at Ferroelectric KNbO3/ATiO3 (A = Sr, Ba, Pb) Interfaces.
Yong Wang 1 , Manish Niranjan 1 , Sitaram Jaswal 1 , Evgeny Tsymbal 1
1 Department of Physics and Astronomy, University of Nebraska-Lincoln, Lincoln, Nebraska, United States
Show AbstractThe demonstration of a quasi-two dimensional electron gas (2DEG) at the LaO/TiO2 interface in LaAlO3/SrTiO3 heterostructures has fuelled intense research activity in recent years [1]. The 2DEG has a high carrier mobility and electron density and is promising for applications in all-oxide electronic devices [2,3]. For such applications it is desirable to have the ability to control the properties of the 2DEG by external stimulus, e.g., by an electric field. For this purpose, in this study we employ density functional calculations to explore all-oxide heterostructures incorporating ferroelectric constituents, i.e. KNbO3/ATiO3 (A = Sr, Ba, Pb) [4]. We find that the polar discontinuity at the (NbO2)+/(AO)0 interfaces in these heterostructures is similar to that at the (LaO)+/(TiO2)0 interface in LaAlO3/SrTiO3 heterostructures. This leads to electronic reconstruction and the formation of a 2DEG at the (NbO2)+/(AO)0 interfaces. We predict that the 2DEG is switchable between two conduction states as controlled by ferroelectric polarization orientation, which can be reversed by an applied electric field. The effect occurs due to the screening charge at the interface that counteracts the depolarizing electric field and depends on polarization orientation. The magnitude of the effect depends on the contrast between polarizations of the two constituents of the heterostructure: the larger is the difference in the two polarizations, the bigger is the effect. For sufficiently large polarization divergence at the interface, we predict a metal-insulator phase transition driven by polarization reversal. We find this behavior for the KNbO3/PbTiO3 interface, where the sizable polarization divergence occurs due to the very large polarization of ferroelectric PbTiO3. Experimentally, the proposed concept of ferroelectrically controlled interface conductivity could be realized, e.g., in a KNbO3/ATiO3 device by incorporating a gate electrode to switch the ferroelectric polarization by applied bias voltage. This concept may be very interesting for memory and logic applications and we hope that our predictions will stimulate experimental studies in this field. 1. A. Ohtomo and H. Y. Hwang, Nature 427, 423 (2004).2. S. Thiel, G. Hammerl, A. Schmehl, C. W. Schneider, and J. Mannhart, Science 313, 1942 (2006).3. C. Cen, S. Thiel, J. Mannhart, and J. Levy, Science 323, 1026 (2009).4. M. K. Niranjan, Y. Wang, S. S. Jaswal, and E. Y. Tsymbal, Phys. Rev. Lett., in press.
9:00 PM - F9.19
Phase-field Modeling of Resistance Degradation of Ferroelectric Dielectrics.
Ye Cao 1 , Saswata Bhattacharya 1 , Clive A. Randall 1 , Long-Qing Chen 1
1 Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania, United States
Show AbstractA phase-field model for predicting the resistance degradation behavior of ferroelectric dielectrics is developed. It takes into account the electrostatic interactions, elastic stress effect, ferroelectric domain structures, presence of grain boundaries, as well as the transport of electronic and ionic defects including oxygen vacancies. Examples to be discussed include single crystal and polycrystalline SrTiO3 and BaTiO3. The effect of the presence of grain boundaries, domain structures, and stress will be discussed.
9:00 PM - F9.2
Phase-field Simulation of Ferroelectric Switching of SrTiO3/BaTiO3 Superlattices.
Pingping Wu 1 2 , Xingqiao Ma 2 , Yulan Li 1 , LongQing Chen 1 , Eftihia Vlahos 1 , Venkatraman Gopalan 1 , Chung Wung Bark 3 , Ho Won Jang 3 , Chad Folkman 3 , Chang-Beom Eom 3 , Xiaoxing Xi 1 4 , Dmitri Tenne 5 , Xiaoqing Pan 6 , Quanxi Jia 7 , Che-Hui Lee 1 , Mike Biegalski 1 , Darrell Schlom 1
1 Department of Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania, United States, 2 Department of Physics, University of Science and Technology Beijing, Beijing, Beijing, China, 3 Department of Materials Science and Engineering, University of Wisconsin, Madison, Wisconsin, United States, 4 Department of Physics, Pennsylvania State University, University Park, Pennsylvania, United States, 5 Department of Physics, Boise State University, Boise, Idaho, United States, 6 Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States, 7 MPA-STC, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractRecent studies have shown that the ferroelectric phase transition temperatures of SrTiO3/BaTiO3 superlattices can be tuned by hundreds of degrees using different stackings of SrTiO3 and BaTiO3 and film/substrate mechanical boundary conditions. It has been shown that the SrTiO3 layers can exhibit significant polarization either induced by the depolarization field from the BaTiO3 layers or as a result of an independent, strain-induced ferroelectric phase transition, leading rather complicated domain structures. The focus of this presentation is on the prediction of the ferroelectric switching hysteresis loops of the superlattices, i.e. P-E loops, under a uniform external electric field using phase-field simulations. The simulations results show that the shape of the hysteresis including the saturated polarization, coercive field, and remnant polarization is strongly dependent on the superlattice superlattice configurations and on the amount of substrate constraint. This work demonstrates the possibility that the shape of the P-E loop can be designed by growing specific SrTiO3/BaTiO3 superlattice configurations and using different substrates. The predicted P-E loops will be compared to experimental measurements.
9:00 PM - F9.20
First-principles Modeling of Finite-temperature Phase Stability in Alkali-based Piezoelectric Perovskites.
Samed Halilov 1 , Marco Fornari 2 , Boris Kozinsky 3 , Nicola Marzari 1
1 DMSE, MIT, Cambridge, Cambridge, Massachusetts, United States, 2 Department of Physics
Mount Pleasant, MI 48859, Central Michigan University, Mount Pleasant, Michigan, United States, 3 Research and technology Center, Robert Bosch, LLC, Cambridge, Massachusetts, United States
Show AbstractThe outstanding piezoelectric performance inalkali-based niobate perovskite alloys such as (A'A"..)NbO3has pointed to these materials as viable and environmentally friendly lead-free substitutes to PZT. We investigate lead-free niobates and titanates using density-functional theory and density-functional perturbationtheory to determine the vibrational free energy of the stable phases and characterize thermal trends. Calculations are performed within the quasiharmonic approximation and include the additional entropic contribution caused by substitutional disorder in all ferroelectric phases. It is shown that there is only relatively small change of entropy related to the transitions between any adjacent structural phases, which gives support to the ferri-electrical natureof polarization in accord with octahedral face-type cation displacement as the main polarization mechanism. The analysis indicates also only a marginal distinctionbetween polymorphic phase (PP) and morphotropic phase (MP)realizations in alkali-based perovskites due to theirclose entropies. Finally, piezolectric coefficients are determined for selected systems using both the Berry-phase calculation of strain-induced polarization and the electric-entalpy approach.
9:00 PM - F9.3
The Role of Defects in BaTiO3.
Hung-Ru Chen 1 , Ben Lui Bin 1 , Colin Freeman 1 , John Harding 1 , Derek Sinclair 1
1 Engineering Materials, University of Sheffield, Sheffield United Kingdom
Show AbstractThe electrical properties of BaTiO3 are very sensitive to chemical dopants and additives. For example, 0.3 at% La on the Ba-site induces semiconductivity at room temperature whereas 0.5 – 2 mol% of Ca on the Ti-site creates ferroelectric ageing with a double P-E hysteresis loop and recoverable electrostrain at room temperature. Furthermore, segregation of transition metal cations such as Mn to the grain boundaries is also known to have a dramatic effect on the electrical properties of the grain boundary regions in BaTiO3 ceramics. Partial phase diagram studies have revealed the extent of solid solubility of Rare Earth (RE) ions in ferroelectric BaTiO3. Large rare earth ions, such as La, dope exclusively on the Ba-site with a large solid solution limit, according to the general formula, Ba1-xLaxTi1-x/4O3 with 0 ≤x≤ 0.25. Intermediate-sized cations such as Gd, show very limited Ba- or Ti-site solubility according to the general formulae, Ba1-xGdxTi1-x/4O3, 0 ≤ x ≤ 0.05 and BaTi1-yGdyO3-y/2 , 0 ≤ y ≤ 0.05, respectively yet show extensive solid solutions according to a self-compensation mechanism, i.e. Ba1-xGd2xTi1-xO3 with 0 ≤ x ≤ 0.20. Small dopants such as Yb, doped exclusively on the Ti-site with a general formula, BaTi1-yYbyO3-y/2, 0 ≤ y ≤ 0.05. Interestingly, the hexagonal polymorph is initially formed as a metastable product for such small RE ions and extended reaction periods at high temperatures, eg 5 days at 1550 oC are required to obtain the thermodynamically stable cubic polymorph. Where the hexagonal polymorph is stabilised, oxygen vacancies are located within the face-sharing dimers. In all cases, the ferroelectric-paraelectric phase transition temperature decreases with RE-doping and the properties range from classic, first-order-type sharp permittivity maxima to broadened ferroelectric-relaxor behaviour. We present a series of simulations using a combination of atomistic and ab initio methods to analyse the behaviour of the defects in the BaTiO3 system. A number of interatomic forcefields were used, including one calibrated against the ab initio simulations. Both cubic and hexagonal phases were considered. The calculations obtain the correct energy different between the phases and demonstrate that that the oxygen vacancies are on the dimers as opposed to corner sharing octahedra. The formation energies of a wide range of possible defects were calculated both in the bulk and at interfaces to investigate the segregation behaviour. The results of calculations on rare-earth dopants are consistent with simple ion size arguments. We discuss the various dopant compensation mechanisms proposed in the cubic and hexagonal phases and their consequences for the electrical properties of the material.
9:00 PM - F9.4
First-principles DFT Study of Grain Boundaries in Ferroelectric PbTiO3.
Pavel Marton 1 , Christian Elsaesser 1
1 , Fraunhofer-Institut fuer Werkstoffmechanik IWM, Freiburg Germany
Show AbstractFunctional devices like electromechanical sensors or actuators are typically made of ferroelectric ceramics of perovskite-type oxides like PbTiO3 or Pb(Zr,Ti)O3. Because of the ceramic polycrystallinity, influences of grain boundaries on the ferroelectric polarisation fields in the grains are important to be considered for the macroscopic performance of devices, but they originate on the microscopic scale and therefore are accessible only by atomic-scale experiments, e.g., transmission electron microscopy (TEM) or atomic force microscopy (AFM), which are very difficult, or by atomic-scale simulation approaches like first-principles density functional theory (DFT). The latter is capable to provide very detailed insight into interfacial atomic arrangements, energetic stabilities, and electronic states at least for model interfaces like symmetrical tilt grain boundaries (STGB) with short coincidence-site-lattice periodicities. In this work, motivated by studies of Sigma=3 STGB in the cubic phase of the dielectric perovskite SrTiO3 [1], first-principles DFT supercell calculations are used to investigate interface effects on the ferroelectricity for several Sigma=3 STGB in the tetragonal phase of the ferroelectric perovskite PbTiO3.[1] S. Hutt et al., J. Phys.: Condens. Matter 13 (2001) 3949[2] N. Benedek et al., Phys. Rev. B 78 (2008) 064110
9:00 PM - F9.5
Ab initio and Atomistic Simulation of the Lead–free Ferroelectric Perovskite Potassium Sodium Niobate Doped with Copper.
Sabine Koerbel 1 , Christian Elsaesser 1
1 , Fraunhofer-Institut fuer Werkstoffmechanik IWM, Freiburg Germany
Show AbstractCurrently lead–free ferroelectric ceramics, one of them the perovskite potassium sodium niobate (KNN), are attracting strong interest in science and technology for being environmentally friendly materials suitable for piezoelectric devices in applications like actuators and sensors.Various doping elements, for instance copper, have been found to improve the ceramic processing conditions and the piezoelectric properties of KNN significantly.Therefore a theoretical understanding of the effects of these impurities is important. Ab-initio density functional theory in the local density approximation and atomistic simulations with empirical interatomic potentials are used in this work to determine the thermodynamically preferred lattice site for copper impurities in KNN as function of processing conditions, and to analyse the influence of the impurities on the energy barriers associated with switching the ferroelectric polarization.
9:00 PM - F9.6
First-principles DFT Study of Ferroelectric Capacitors of Ultrathin PbTiO3 Films Between Symmetric or Asymmetric Electrodes.
Yoshitaka Umeno 1 3 , Jan-Michael Albina 2 , Bernd Meyer 4 , Christian Elsaesser 2 3 , Peter Gumbsch 2 3
1 Institute of Industrial Science, The University of Tokyo, Tokyo Japan, 3 IZBS, University of Karlsruhe, Karlsruhe Germany, 2 , Fraunhofer-Institut fuer Werkstoffmechanik IWM, Freiburg Germany, 4 ICMM and CCC, University of Erlangen-Nuernberg, Erlangen Germany
Show AbstractUltrathin capacitors of ferroelectric perovskite films between conducting electrodes, which can be grown epitaxially on perovskite substrates with thickness down to only few unit cells and nearly perfect interfaces, have very attractive perspectives, for instance as non-volatile ferroelectric random access memory components. Two important issues for such nano-sized ferroelectric components are the critical film thickness, below which ferroelectricity is unstable. and Schottky barriers at the film/electrode interfaces, which must be sufficiently high to prevent the loss of ferroelectric polarisation by leakage currents. As a model study, in this work (001)-oriented and 2-6 unit cells thick PbTiO3 films sandwiched between two equal or unequal (001)-oriented electrodes are investigated by first-principles density-functional-theory (DFT) in the local density approximation (LDA) using a mixed-basis pseudopotential supercell approach. The two considered electrode materials are the transition metal Pt and the conducting perovskite-type oxide SrRuO3, both having a small lattice mismatch to PbTiO3. Related a previous DFT investigation for symmetric Pt/PbTiO3/Pt capacitors [1] the stability of ferroelectricity as function of the thickness and the lateral elastic strain is calculated and analyzed for symmetric SrRuO3/PbTiO3/SrRuO3 and asymmetric Pt/PbTiO3/SrRuO3 capacitors. Following another recent DFT investigation for dielectric metal/SrTiO3/metal [2] and oxide/SrTiO3/oxide [3] capacitors, Schottky barriers at the interfaces and electrostatic potential profiles are calculated and the influence of the ferroelectric polarisation on the Schottky barriers is discussed.[1] Y. Umeno et al., Phys. Rev. B 74 (2006) 060101[2] M. Mrovec et al., Phys. Rev. B 79 (2009) 245121[3] J.-M. Albina et al., Phys. Rev. B 76 (2007) 165103
9:00 PM - F9.7
Vortex Structure Transformation of BaTiO3 Nanoparticles Through the Gradient Function by Phase Field Method.
Liang Hong 1 , Ai Kah Soh 1
1 Mechanical Engineering, The University of Hong Kong, Hong Kong China
Show AbstractTransformation of the vortex structures (VS) in a single BTO nanoparticle has been found to be related with the variation of the coefficients of the domain wall energy at room temperature. Note that the tetragonal VS is defined as one with its vortex direction pointing along the tetragonal direction; and the other types of VSs, i.e., orthorhombic, monoclinic and rhombohedral are also defined in similar manner.The phase field method is employed to devise a three-dimensional BTO nanoparticle model under open-circuit condition, where the ferroelectric core part is embedded in a non-polarization medium to represent an individual nanostructure. An eighth-order polynomial for the Landau-Devonshire potential has been considered as the bulk energy in this model to produce the monoclinic polarization dipoles.Through the modulation of the gradient coefficients, vortices of the BTO nanoparticle are found to transform in a path of monoclinic MA → orthorhombic → monoclinic MC → tetragonal. The total net polarization is null regardless of the type of vortex structures considered and, therefore, it is not suitable for differentiating between VSs. But the ratio between the three toroidal moment components, Gx, Gy and Gz, can be used to determine the vortex direction and, thus, classifies the VSs into different categories.It has been found that the rotation and magnitude reduction of polarization dipoles would increase the bulk energy, hence, inducing the vortex transformation process in BTO nanoparticles. Since vortex exists in the whole transformation, the electrostatic energy is minimized to close to zero for all VSs. The change of gradient energy is remarkably small compared with the variation of the gradient coefficients due to the competitive increase of the bulk energy, which arises from the rotation as well as magnitude reduction of polarization dipoles. The obvious increase of bulk energy dominates the change of the total energy throughout this nanoparticle's transformation process. The larger the gradient coefficient is, the smaller is the bulk energy in magnitude, and the lesser is the averaged magnitude of polarization dipoles.Moreover, the existence of monoclinic phase is a necessity to start the vortex transformation process. When the eighth-order bulk energy polynomial is replaced with a sixth-order one in the BTO nanoparticle model, no clear VS transformation is found. This is probably due to the fact that the sixth-order bulk energy cannot support a monoclinic phase in BTO.
9:00 PM - F9.8
Geometric Phase Analysis of Nano-Scale Strain Fields Around 90° Domains in PbTiO3/SrTiO3 Epitaxial Thin Film.
Takanori Kiguchi 1 2 , Kenta Aoyagi 3 , Toyohiko Konno 1 2 , Satoru Utsugi 4 , Tomoaki Yamada 4 , Hiroshi Funakubo 4
1 Institute for Materials Research, Tohoku University, Sendai, Miyagi, Japan, 2 Center for Integrated NanoTechnology Support, Tohoku University, Sendai, Miyagi, Japan, 3 Department of Materials Science, Tohoku University, Sendai, Miyagi, Japan, 4 Department of Innovative and Engineered Materials, Tokyo Institute of Technology, Yokohama, Kanagawa, Japan
Show AbstractPbTiO3 is a representative ferroelectric material with large tetragonality and polarization. The 90° domain configuration is important for its ferroelectric and piezoelectric properties, and is affected from the film thickness through the residual strain. Recently, Nakaki et al. have found, using an XRD technique, that the 90° domain configurations of PbTiO3 films on SrTiO3 substrates can be classified to three types (types I, II, and III) according to the thickness of the PbTiO3 layer [1]. The XRD study have elucidated that the type I is the complete c-domain configuration, the type II the a-c mixed one, and the type III the complex one. These configurations depend strongly on the film thickness through the residual strain. However, an XRD technique is not able to detect the real space information, e.g. the interaction of the 90° domain with the film/substrate interface or misfit dislocations. In particular, it is important for the type II and III configuration to understand the interaction.The purpose of the present study is to elucidate the domain structure of type II PbTiO3 film epitaxially grown on SrTiO3 (001) substrate by pulsed-MOCVD in the atomic resolution by HAADF-STEM (TITAN80-300, 300kV, FEI), and to visualize the two-dimensional strain field in the film with nm resolution by using the geometric phase analysis (GPA, HREM Research Inc.) [2]. Our results show that the films typically possess a-c mixed domain configuration with misfit and threading dislocations. Most of the a-domains are penetrating the film to the surface, while some of them are terminated within the film and are short in length. On the other hand, the bottom of the a-domain does not penetrate the film across the film/substrate interface. It keeps away from the interface. There is completely c-domain layer under the a-domain. This result shows that the domain configuration regarded as the type II by an XRD measurement is composed from two layered configurations, the type II layer of about 300nm on the type I layer of 5nm. The GPA shows that the c-axis in the type I layer is longer than that in the upper region. In contrast, a-axis in both layer have only little difference. Thus, the type I domain configuration remains just above the interface with larger tetragonality. Furthermore, two misfit dislocations with burgers vector b=〈100〉 locate at the bottom of the a-domain. The lattice tilt of a-domain originates from the dislocation.These results reveal that the complex strain field between the type I and II configuration layers makes it possible to leave the type I configuration, and infers that the misfit dislocation would be the starting point for a-domain formation through the lattice tilt around the dislocation core.[1] H. Nakaki, Y.-K. Kim, S. Yokoyama, R. Ikariyama, H. Funakubo, K. Nishida, and K. Saito, Appl. Phys. Lett. 91, 112904 (2007)[2] M.J. Hÿtch, E. Snoeck, and R. Kilaas, Ultramicroscopy, 74, 131-146 (1998)
9:00 PM - F9.9
First-principles Investigation of Edged Ferroelectric PbTiO3 Nanowires and the Role of Axial Strain.
Takahiro Shimada 1 , Shogo Tomoda 1 , Takayuki Kitamura 1
1 Department of Mechanical Engineering and Science, Materials Science Laboratory, Kyoto University, Kyoto Japan
Show AbstractWe have investigated the atomistic and electronic structures of PbTiO3 nanowires with characteristic edges consisting of (100) and (010) perovskite surfaces and the crucial role of axial tensile strain on ferroelectricity using first-principles density-functional theory (DFT) calculations. Ferroelectricity is highly enhanced at the edge of the PbO-terminated nanowire because the Pb-O covalent bond that governs the ferroelectric distortions is locally strengthened. On the other hand, a significant suppression is found in the TiO2-terminated nanowire, which is caused by the charge transfer from the Pb-O site to the Ti-O site. Surprisingly, the smallest PbO-terminated nanowire with a cross section of only one-unit-cell can maintain ferroelectricity, while ferroelectricity disappears in the TiO2-terminated nanowires with a cross section smaller than four-by-four cells (diameter of about 17 Å). However, ferroelectricity is recovered by axial tension, where the thinner nanowire requires the higher critical strain.
Symposium Organizers
Alexei Gruverman University of Nebraska-Lincoln
Craig J. Fennie Cornell University
Iwao Kunishima Toshiba Corporation
Beatriz Noheda University of Groningen
Tae Won Noh Seoul National University
F10: Applications and Nanostructures
Session Chairs
Marty Gregg
Iwao Kunishima
Thursday AM, December 03, 2009
Grand Ballroom (Sheraton)
9:00 AM - **F10.1
The Effects of Size and Shape on the Properties of Single Crystal Nanoscale Ferroelectrics
A. Schilling 1 , G. Catalan 2 , J. Scott 2 , J. Gregg 1
1 School of Maths and Physics, Queen's University Belfast, Belfast United Kingdom, 2 Department of Earth Sciences, University of Cambridge, Cambridge United Kingdom
Show AbstractIn theory, the performance of many electronic devices could be dramatically enhanced by incorporating ferroelectric materials into their structures. Ferroelectrics have a lot to offer: the reversible remanent polarization, which defines the ferroelectric, can be used for both non-volatile binary data storage and for altering local electric fields in field-effect transistors; high permittivities can be used for efficient dynamic charge storage in DRAM; and the degree to which the permittivity can be altered using bias electric fields (tunability) makes ferroelectrics extremely useful for smart antennae, as well as for photonic and plasmonic devices where field-controlled variations in refractive index are needed. In practice, it is a frustrating irony that the key functional properties that make ferroelectric materials so attractive in the first place are almost universally observed to be degraded when at the nanoscale, often needed in high-tech devices. In general, coercive fields increase, tunability decreases and permittivities are severely suppressed, often by several orders of magnitude. Despite decades of research, fundamental reasons as to why property changes occur have remained unclear. Much of the confusion and debate stems from a paucity of clean, clear-cut experiments. Recently, research teams mainly in Queen’s University Belfast and the University of Cambridge have attempted to gain clearer insight into the manner in which nanoscale size and changes in morphology affect ferroelectric behaviour, by mapping the properties of single crystal ferroelectric nanoshapes cut from bulk using a Focused Ion Beam Microscope (FIB). Permittivity characteristics, static domain configurations and the dynamics of switching have been examined in thin film plates, nanorods and nanodots, and a summary of the findings will be presented. In general the research has allowed for the following statements:(i)in contrast to observations made on conventional thin films systems, the permittivity characteristics of thin single crystal BaTiO3 with both gold and platinum electrodes behave almost exactly as seen in bulk; this immunity to reduced size is not universal, however, as the same experiments performed with SrTiO3 and platinum electrodes reveal dramatic permittivity suppression consistent with dielectric ‘dead-layers’ at electrode-dielectric interfaces. Remarkably these observations have been successfully rationalized using atomistic simulations by Stengel, Spaldin and Vanderbi<(ii)the domain states present in ferroelectric nanoshapes satisfy the simultaneous desire to preserve shape on cooling through the Curie temperature, and minimize the energy associated with depolarizing fields.(iii)switching in nanorods appears easier than in thin film plates, and the kinds of morphological pinning centres seen to be effective in ferromagnetic research (such as notches in nanowires) appear to have little impact.
9:30 AM - **F10.2
Characterization of Polar-axis-oriented Epitaxial Pb(Zr, Ti)O3 Thick Films.
Hiroshi Funakubo 1 , Takashi Fujisawa 1 , Hiroshi Nakaki 1 , Satoru Utsugi 1 , Hitoshi Morioka 2 1 , Takashi Iijima 3 , Osami Sakata 4 , Mutsuo Ishikawa 1 , Tomoaki Yamada 1
1 , Tokyo Institute of Technology, Yokohama, Kanagawa, Japan, 2 , Bruker AXS, Yokohama Japan, 3 , AIST, Tsukuba Japan, 4 , JASRI, Saya Japan
Show AbstractCharacterization of polar-axis oriented PZT is important in view of the fundamental and real applications because of the difficulty for making single crystal. Only thin films below 200 nm has been successfully grown for polar-axis orientation, but thicker films are highly required from the view points of piezoelectric and optoelectric properties. We reported on the successful growth of plar-axis-oriented tetragonal Pb(Zr0.35Ti0.65)O3 films above 2 μm in thickness on (100)CaF2 substrates with SrRuO3 buffer layer by metal organic chemical vapor deposition. Volume fraction of (001) orientation in the mixture orientation of (100) and (001) was linearly increased with increasing the thermal expansion coefficient of the substrate and perfectly (001)-oriented films were grown on (100)CaF2 substrates with large thermal expansion coefficient. The lattice parameters of the obtained films were almost independent of the film thickness and was almost the same with the reported data for Pb(Zr0.35Ti0.65)O3 powder, suggesting the small residual strain in the films. Estimated relative dielectric constant at room temperature and 4.2 K taking account of the dead layer was 150 and 88, respectively, in good agreement with the expected one from the theory. Well saturated polarization-electric-field hysteresis loops with a good square shape were observed at room temperature and the spontaneous polarization was 71 μC/cm2. In addition, the d33 value was estimated to be about 70 pm/V by the PFM and the Synchrotron XRD measurement almost agreed with the theoretical prediction based on the clamping model. Ref. 1) T. Fujisawa et al., Appl. Phys. Exp. 1 (2008) 085001. 2) T. Fujisawa et al., J. Appl. Phys. 105 (2009) 061614.3) T.Fujisawa et al., Mater.Res.Soc.Proc., 1129 (2009) 1129-V11-02.
10:00 AM - F10.3
Piezoelectric Thin Films for a High Frequency Ultrasound Transducer with Integrated Electronics.
Flavio Griggio 1 , Hyunsoo Kim 2 , Insoo Kim 3 , Thomas Jackson 2 , Kyusun Choi 3 , Richard Tutwiler 4 , Susan Trolier-McKinstry 1
1 Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania, United States, 2 Center for Thin Film Devices and Department of Electrical Engineering, The Pennsylvania State University, University Park, Pennsylvania, United States, 3 Department of Computer Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania, United States, 4 Applied Research Laboratory, The Pennsylvania State University, University Park, Pennsylvania, United States
Show AbstractFerroelectric films possess high piezoelectric response and so they are suitable for high sensitivity sensors and low voltage actuators. The object of this research is to explore thin film piezoelectrics on larger resonating structures as a means to realize high frequency array transducers. PZT (PbZr1-xTixO3) and PNN-PZT (PbZr1-xTixO3 – PbNi1/3Nb2/3O3) thin films were utilized as the piezoelectric material. The thin films were obtained via chemical solution deposition using 2-methoxyethanol (2-MOE) as a solvent. This paper will compare the properties of PNN-PZT films prepared under a variety of temperature treatment conditions and compositions. The best properties were achieved with {100}-textured films. It was found that for films under a micron in thickness, the dielectric constant varied between 1400 and 1900 while the remanent polarization ranged between 21 and 25 μC/cm2 and e31,f from –5 to –10.6 C/m2. The Curie temperature for the 30PNN-70PZT composition is 260 oC.These films were then integrated into one dimensional array transducers. The geometry used for transducer arrays is a xylophone-bar type with a length:width aspect ratio greater than 5:1 in order to isolate the length and width extensional modes. For this purpose, the PZT and remaining films in the stack were patterned using ion-beam etching and partially released from the underlying silicon substrate by XeF2 etching. Impedance measurements on the fabricated structures showed resonance frequencies between 3 and 70 MHz for fully and partially released structures depending on the transducer dimensions and vibration modes. In-water transmit and receive functionalities have been demonstrated. A bandwidth of receive of 60 % has been determined for partially released structures at 60 MHz center frequency.A CMOS ASIC control chip was designed and prototyped for the ultrasound transducer. It contains 16 receive and transmit channels with preamplifiers, time-gain compensation amplifiers, a multiplexed analog/digital converter with 3 Kbyte of non-chip SRAM, and 50 MHz resolution time delayed excitation pulse generators.
10:15 AM - F10.4
Pulse Excimer Laser Annealing of Ferroelectric Thin Films for MEMs Applications.
Bharadwaja Srowthi 1 , J. Kulik 1 , R. Akarapu 2 , H. Beratan 3 , S. Trolier-McKinstry 1
1 Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania, United States, 2 , The Pennsylvania State University, University Park, Pennsylvania, United States, 3 , L-3 Communications IP, Dallas, Texas, United States
Show AbstractFerroelectric thin films have received wide attention because of their growing use in nonvolatile memories, pyroelectric detectors, miniaturized piezoelectric transducers and tunable microwave devices. However, Pb based ferroelectric thin films are often crystallized at temperatures ≥ 600 oC in order to maximize the functional properties. Such high crystallization temperatures preclude the processing of pyroelectric detectors directly on CMOS, as the underlying read-out-integrated-circuitry (ROIC) cannot withstand such high temperatures. Therefore, there is a considerable interest in lowering the crystallization temperatures of ferroelectric thin films to enable direct integration with CMOS technology. More generally, an annealing process which enables low substrate temperatures would be useful for deposition of dielectric, piezoelectric, and electro-optic films on polymeric, or other temperature-sensitive substrates. In this presentation, an alternative way to crystallize ferroelectric layers below substrate temperatures of 400 oC using pulsed excimer lasers will be discussed. The influence of laser operating parameters, the ambient gas, and the substrate temperature on the crystallization of Pb- based ferroelectric thin films were investigated. The dielectric, loss tangent and pyroelectric properties of laser annealed PZT 30/70 films are 475, < 5%, and 21 nC/cm2K respectively. All of these are comparable with those of films rapid thermal annealed at 650 oC. In addition, finite element simulations of heat propagation and the associated temperature distribution across the film stacks, along with the rate dependent and non-isothermal crystallization kinetics during pulse excimer laser annealing will be presented. These simulation results, along with transmission microscopy studies, suggest that crystallization is limited by nucleation, rather than growth. Further, the possibility of integrating the Pb-based ferroelectric thin films onto polymer substrates (polyimides) will be discussed.
10:30 AM - F10.5
Hybrid Multiferroic Ferroelectric/Semiconductor System: Towards a Low-voltage Non-volatile Ferroelectric Transistor.
Sebastian Riester 1 , Igor Stolichnov 1 , H. Trodahl 1 2 , Nava Setter 1 , Andrew Rushforth 3 , Kevin Edmonds 3 , Richard Campion 3 , C. Foxon 3 , Bryan Gallagher 3 , Tomas Jungwirth 4 3
1 Ceramics Laboratory, EPFL- Swiss Federal Institute of Technology, Lausanne Switzerland, 2 MacDiarmid Institute for Advanced Materials and Nanotechnology, Victoria University, Wellington New Zealand, 3 School of Physics and Astronomy, University of Nottingham, Nottingham United Kingdom, 4 Institute of Physics, ASCR v.v.i., Cukrovarnická 10 , Prague Czechia
Show AbstractIn the ferromagnetic semiconductor (Ga,Mn)As, the magnetic interaction between the substitutional Mn2+ ions is mediated by the strongly spin-orbit coupled valence band holes. This results in a strong dependence on the Curie temperature (Tc) upon changes in the carrier density, which opens wide opportunities for the field effect control of ferromagnetism[1]. The ferroelectric gate field effect transistor (FET) with a ferromagnetic (Ga,Mn)As conducting channel gated by a ferroelectric co-polymer polyvinylidene fluoride with trifluoroethylene P(VDF-TrFE) reported earlier2 adds to the system a new functionality of non-volatile control of ferromagnetism producing a persistent change of Curie temperature Tc in the magnetic channel. Conventional FET structures on dilute magnetic semiconductors require a rather high poling voltage[2] due to a high concentration of charge carriers required for the ferromagnetic coupling. The advantages of PVDF ferroelectric gates include the relatively easy scalability of the thickness and hence poling voltage, which is important for compatibility with low-voltage TTL circuitry[3]. Additionally the persistent control of ferromagnetism in the ferroelectric/semiconductor sandwich opens opportunities for engineering ferromagnetic patterns by rewritable nanoscale control of ferroelectric domains in the gate.Here, we report the latest progress in maximizing the gate effect and thus functionality of the multiferroic device, aiming at a stronger degree of control over the ferromagnetism by ferroelectricity. Various techniques for treating the ferroelectric interface including electrical and mechanical stress, in combination with different temperature profiles, resulted in a considerable improvement of the gate effect as probed by magnetotransport measurements. References:[1] Chiba, D., Matsukura, F. & Ohno, H. Electric-field control of ferromagnetism in (Ga,Mn)As. Applied Physics Letters 89, 162505 (2006).[2] Stolichnov, I., Riester, S.W.E., Trodahl, H.J., Setter, N., Rushforth, A.W., Edmonds, K.W., Campion, R.P., Foxon, C.T., Gallagher, B.L. & Jungwirth, T. Non-volatile ferroelectric control of ferromagnetism in (Ga, Mn)As. Nature Materials 7, 464-467 (2008).[3] Riester, S.W.E., Stolichnov, I., Trodahl, H.J., Setter, N., Rushforth, A.W., Edmonds, K.W., Campion, R.P., Foxon, C.T., Gallagher, B.L. & Jungwirth, T. Toward a low-voltage multiferroic transistor: Magnetic (Ga,Mn)As under ferroelectric control. Applied Physics Letters 94, 063504 (2009).
10:45 AM - F10.6
Fe-NAND Flash-memory Application of Ferroelectric Gate FETs.
Mitsue Takahashi 1 , Shouyu Wang 1 , Ken Takeuchi 2 , Shigeki Sakai 1
1 , National Institute of Advanced Industrial Science and Technology, Tsukuba Japan, 2 Dept. of Electrical Engineering and Information Systems, University of Tokyo, Tokyo Japan
Show AbstractVery recently a novel NAND flash memory using ferroelectric-gate FET (FeFET) memory cells has been introduced and called ferroelectric (Fe-) NAND [1]. The Fe-NAND flash memory has two significant advantages over the conventional floating-gate (FG) type NAND. One is a good scalability. The Fe-NAND flash memory has a potential for downsizing below 20nm because the capacitance-coupling noise will not be significant. The other is having very good electric properties. The Fe-NAND memory cell has the program-and-erase (P/E) endurance over 10^8 times by 6V and 10μs-wide P/E pulse application [1]. The memory cells and select-gate transistors were all n-channel-type Pt/SrBi2Ta2O9 (SBT)/Hf-Al-O/Si FeFETs. The film thicknesses of Pt, SBT, and Hf-Al-O were typically 200nm, 400 - 600nm, and 7nm, respectively. The gate length and width were 7µm and 50µm. In this study, we demonstrated the Fe-NAND operations of erase, program and read operations of arrayed Fe-NAND flash memory cell were demonstrated for the first time, as well as a single cell performance. The memory array included 8 cells on the cross-points of 4 word-lines by 2 NAND strings. There were 256 programmed patterns in the 4 × 2 miniature Fe-NAND cell array which gave us good information to know read-data distribution of an assumed large-scale Fe-NAND. The erase was performed by applying 10µs-wide 7V pulses to p- and n-wells. The program was performed by applying 10µs-wide 7V pulses to selected word-lines. Bit-line-current distribution was obtained by reading 51 programmed patterns out of 256 in all. The accumulated read currents successfully made a distribution of the two distinguishable “0” and “1” states. The margin between the two states became wider by applying a verification technique on a cell. Retention times of bit-line currents were obtained over 33 hours for both the “0” and “1” states in a randomly chosen program pattern. The 4 × 2 cell array was also a useful model for investigating disturb problems of unselected cells. There were two significant program disturbs in an Fe-NAND flash memory as well as in an FG-NAND. One is called Vpgm disturb which affects unselected cells sharing a word-line with the selected cell. The other is called Vpass disturb which affects unselected cells sharing a NAND string with the selected cell. The influence of disturbs on an Fe-NAND flash-memory performance were estimated by measuring electrical properties of a single Fe-NAND memory cell or an FeFET with assumed voltage conditions. This work was partially supported by the New Energy and Industrial Technology Development Organization (NEDO). [1]S. Sakai, et al., Proc. of the 2008 23rd IEEE Non-Volatile Semiconductor Memory Workshop, pp.103-105.
11:30 AM - F10.7
High Performance of Single-crystal-like Ferroelectric Thin Films on Flexible, Low-cost, Metal Templates for Ferroelectric Applications.
Junsoo Shin 1 , Amit Goyal 1
1 Materials Science & Technology Division, Oak Ridge National Laboratory, Oak Ridge , Tennessee, United States
Show AbstractIn most ferroelectric applications, high quality thin films are required for fabrication of electronic devices such as nonvolatile random access memories, but conventional, epitaxial films have been deposited on various single crystal substrates. These substrates have disadvantages of expensive cost, rigidity and availability in only very limited sizes. For this reason, a few groups recently reported the deposition of polycrystalline lead-based compounds on copper foils. However, randomly oriented polycrystalline films have a large suppression of ferroelectric properties. We report fabrication of single-crystal-like, epitaxial lead-free ferroelectric thin films (BaTiO3 and BiFeO3) on metallic Ni-alloy via pulsed laser deposition. The textures, the microstructure of ferroelectric domains and switching of the local polarization, and the macroscopic polarization hysteresis of the samples were characterized using a 4-circle X-ray diffractometer, piezoresponse force microscopy and spectroscopy and a ferroelectric tester. The performance values obtained are comparable to that reported for ferroelectric films on single crystal substrates.
11:45 AM - F10.8
Exploration of All-Thin-Film Non-Volatile ME RAM Devices.
Arun Luykx 1 , Samuel Lofland 2 , Daisuke Kan 1 , Dwight Hunter 1 , Fransiska Kartawidjaja 4 , Anbusathaiah Varatharajan 3 , John Wang 4 , Valanoor Nagarajan 3 , John Cumings 1 , Ichiro Takeuchi 1
1 Materials Engineering, University of Maryland, College Park, Maryland, United States, 2 Department of Physics, Rowan University, Glassboro, New Jersey, United States, 4 Deptartment of Materials Science and Engineering, National University of Singapore, Singapore Singapore, 3 Deptartment of Materials Science and Engineering, University of New South Wales, Sydney, New South Wales, Australia
Show AbstractWe are exploring various geometry multiferroic thin-film heterostructures in order to investigate the feasibility of fabricating electric-field tuneable non-volatile multiferroic magnetic RAM devices. Our multiferroic structures consist of a patterned magnetostrictive FeGa film (100 nm) sputtered on top of a sol-gel derived PbZr0.3Ti0.7O3/PbZr0.7Ti0.3O3 (70 nm/70 nm) bilayer grown on Pt/Ti/SiO2/Si substrates. We have previously demonstrated that the PZT bilayer displays electric-field reversible non-volatile ferroelastic domains (Anbusathaiah et al., Advanced Materials (2009)). The present devices exploit direct elastic coupling of these domains with the magnetostrictive layer. The electric-field tuned elastic states in the bilayer are transferred to the FeGa layer resulting in modified magnetic anisotropy. For the initial feasibility investigation, we have patterned the FeGa layer into 20 x 20 (μm)2 pads, which also serve as electrodes for applying electric-field to the PZT bilayer. We probe the change in magnetic properties of the magnetostrictive layer as a function of applied electric field using ferromagnetic resonance (FMR) at 9.3 GHz. Following application of 170 kV/cm for 5 sec, a shift in the magnetic field position of the main FMR peak by up to 34% (440 Oe) is observed indicating induced change in magnetic anisotropy due to the motion of ferroelastic domains in the PZT layer. Subsequent applications of alternating pulses of + and – 170 kV/cm result in reversible changes in the FMR peak position. We will also report on the magnetoresistance devices based on the FeGa/PZT bilayers.This work is supported by NSF MRSEC at UMD (DMR 0520471), ARO W911NF-07-1-0410, and ONR N000140610530.
12:00 PM - F10.9
Development of Ferroelectric Data Storage Test System for High-Density and High-Speed Read/Write.
Yoshiomi Hiranaga 1 , Kenkou Tanaka 1 , Tomoya Uda 1 , Yuichi Kurihashi 1 , Yasuhiro Kimoto 1 , Hikari Tochishita 2 , Michio Kadota 2 , Yasuo Cho 1
1 , Research Institute of Electrical Communication, Tohoku University, Sendai Japan, 2 , Murata Manufacturing Co., Ltd., Yasu, Shiga, Japan
Show AbstractFerroelectric probe data storage is one of the promising candidates for next generation high density data storage devices. In this study, we have developed ferroelectric data storage test systems based on scanning nonlinear dielectric microscopy (SNDM) to conduct various experiments concerning read/write capability.[1,2] Additionally, ultra-thin (< 50 nm) LiTaO3 single crystal recording media were prepared in order to realize high-density and high-speed read/write. Epitaxial LiTaO3 thin film recording media were also prepared by metal organic chemical vapor deposition aiming at low-cost mass-production.At first, we have conducted several fundamental experiments using a linear-scanner-type data storage test system equipped with a triaxial piezo actuator. Using this system, real information data was successfully recorded on the LiTaO3 single crystal medium with areal density of 3.9 Tbit/inch2. The bit size was as small as 12.8 nm. Additionally, close-packed domain dot array formation on the epitaxial LiTaO3 film with areal density of 1.6 Tbit/inch2 was also succeeded. It suggests that nanoscopic crystallinity of the thin film was excellent, although not to the extent of that of single crystals.Subsequently, we have developed a hard-disk-drive-type ferroelectric data storage test system equipped with a high-accuracy spindle motor for conducting read/write tests under conditions close to those of actual operation. For readout tests using the developed system, a periodically inverted signal, which was corresponding to artificial domain stripes formed on the LiTaO3 single crystal, was observed. The readout signal was correctly demodulated with a bit rate of up to 2 Mbps. Writing tests were also conducted using the epitaxial thin film recording media, and a bit data array was successfully recorded on the film with a bit rate of up to 20 Mbps. These results revealed that the read/write method based on SNDM can achieve high-speed data transfer compared with other probe data storage methods proposed to date, and has a large potential for realization of applicative bit rates using single-probe heads.In addition, a non-contact probe-height control technique was adopted to solve the problem of tip abrasion using higher-order nonlinear dielectric response detection method.[3] The gap distance between the probe and the medium surface was controlled to be 1.7 nm under readout operations. Inverted domain dot with a diameter of less than 100 nm could be formed under the non-contact state. The achievement of nanoscale gap control is considered to have potential in providing a breakthrough in the field of probe data storage by solving the problem of tip abrasion.[1] Y. Hiranaga et.al.: IEEE Trans. Ultrason., Ferroelect., Freq. Contr. 54 (2007) 2523.[2] K. Tanaka et.al.: Jpn. J. Appl. Phys. 47 (2008) 3311.[3] R. Hirose, K. Ohara and Y. Cho: Nanotechnology 18 (2007) 084014.
12:15 PM - F10.10
3-D Reconstruction of Ferroelectric Domain Structures in PbTiO3 Nanotubes.
Sunmi Moon 1 , Yunseok Kim 2 , Changdeuck Bae 3 , Hyunjun Yoo 1 , Youngjin Yoon 1 , Jooho Moon 3 , Jang-Sik Lee 4 , Seungbum Hong 5 , Kwangsoo No 6 , Hyunjung Shin 1
1 National Research Laboratory for Nanotubular Structures of Oxides, Center for Materials and Processes of Self-Assembly, and School of Advanced Materials Engineering, Kookmin University, Seoul Korea (the Republic of), 2 , Max Planck Institute of Microstructure Physics, Halle Germany, 3 Materials Science and Engineering, Yonsei University, Seoul Korea (the Republic of), 4 Center for Materials and Processes of Self-Assembly, and School of Advanced Materials Engineering, Kookmin University, Seoul Korea (the Republic of), 5 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States, 6 Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Daejeon Korea (the Republic of)
Show Abstract One-dimensional (1-D) ferroelectric nanostructures have been recently attracting much interest because they offer promising routes to the realization of high-efficient, miniaturized sensors, and transducers for the applications of energy generators and memory devices. Up to now, several synthesis techniques of ferroelectric nanowires (NWs) and nanotubes (NTs) have been proposed including infiltration, molten salt technique, and sol–gel coatings on the inside of porous templates. Here, we fabricated controlled ferroelectric PbTiO3 (PTO) NTs by the direct reaction of crystalline anatase TiO2 NTs with gas-phase of PbO powder. TiO2 NTs served as starting materials were fabricated by template-directed atomic layer deposition (ALD) process onto porous alumina membranes. With the ALD process, all of the physical dimensions of TiO2 NTs are readily adjustable and then these directly determine the final dimensions of the resulting PTO NTs. Domain analysis of the ferroelectric NTs becomes extremely important to understand their characteristic complex domain structures distinguished from 2-D as well as bulk materials. Visualization of the detailed domain structures and manipulation of polarization states on 1-D ferroelectric nanostructures have not been reported yet. In this presentation, we’ve been focused on the 3-D polarization distribution of complex ferroelectric domain structures in the PTO NTs using piezoresponse force microscopy (PFM). Using vector PFM, the domain arrangement in PTO NTs was obtained along all three components of the x-, y- and z-axes from the lateral and vertical PFM images at in-plane angles of 0° and 90°. Since the typical piezoresponse mapping has information of only the polarization components of Px and Pz, its LPFM images should be recorded twice with/without physical rotation by 90° in order to obtain Py polarization component on our PTO NTs, thus allowing the complete in-plane information on the polarization vector in NTs. The information of Px, Py, and Pz enables us to reconstruct the 3-D domain configuration. Interestingly, we found a region where a grain in NT has a seemingly single domain in terms of out-of-plane polarization information, but in fact a polydomains divided by 90° domain wall as evidenced by x- and y- axes in-plane polarization information. In addition, we found a single domain consisted of multiple grains, which demonstrates an example of decoupling of the domain boundary with the grain boundary in polycrystalline PTO NTs.
F11: Structural Properties and Size Effects
Session Chairs
Claude Ederer
Beatriz Noheda
Thursday PM, December 03, 2009
Grand Ballroom (Sheraton)
2:30 PM - **F11.1
Physics of Multiferroic Hexagonal (Y,Lu)MnO3.
Seongsu Lee 1 2 , Jung-Hyun Lee 1 , Kwang-Hyun Jang 1 , Junghwan Park 1 3 , Sang-Wook Cheong 4 , Je-Geun Park 1 3
1 Department of Physics , SungKyunKwan University, Suwon Korea (the Republic of), 2 Neutron Science Division, Korea Atomic Energy Research Institute, Daejeon Korea (the Republic of), 3 Department of Energy Science, SungKyunKwan University, Suwon Korea (the Republic of), 4 Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey, United States
Show AbstractWe are living in the world, of which modern life is crucially dependent on materials having either ferroelectricity or magnetism one way or another. Despite numerous examples exhibiting one of the two ground states, therefore it is surprising to learn that in nature there are relatively very few materials having both properties in a single compound. These so-called multiferroic systems with both ferroelectricity and magnetic states have recently been the focus of extensive researches worldwide due to their unique physical properties as well as immense technical potentials.Hexagonal RMnO3 shows a ferroelectric transition at relatively high temperatures around 800 ~ 900 K and becomes antiferromagnetically ordered below 100 K. What makes the magnetic ground state of RMnO3 unique is that it occurs in the natural two dimensional triangular networks of Mn moments. This geometrical aspect of the magnetic order together with the multiferroic behavior renders hexagonal RMnO3 all the more interesting. In order to understand the unusual physical properties of RMnO3, in particular a possible coupling between the magnetic and ferroelectric order parameters, we have undertaken various experimental and theoretical approaches. In this talk, we will present some of key results and explain how we have investigated the hexagonal manganites using bulk measurements as well as microscopic tools such as neutrons. We will also present results on other multiferroic materials apparently sharing similar features and discuss their common physics.
3:00 PM - **F11.2
PDF Studies of Size and Substitution Effects in BaTiO3.
Ram Seshadri 1 , Katharine Page 2
1 Materials, UC Santa Barbara, Santa Barbara, California, United States, 2 LANSCE, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractIn the first part of this talk, we explore the effects of size in nanoparticulate BaTiO3 studied using synchrotron X-ray and neutron pair distribution functions. We find with high quality nanoparticles that despite the smaller particles (including 4.7 nm particles) appearing to be more cubic, local polar distortions persist even at the smallest sizes. In the second part, we discuss the curious puzzle of perovskite SrTiO3, which becomes metallic with 0.03% to 0.1% Nb substitution on the Ti site, while BaTiO3 remains insulating above 10% Nb substitution. Given the nearly identical structure and electron counts of the two materials, the distinct ground states for low substitution have been a long-standing puzzle. We find from neutron studies of average and local structure the subtle yet critical difference that we believe underpins the distinct electronic properties in these fascinating materials.
3:30 PM - F11.3
Revisiting Ferroelectric Tetragonal Tungsten Bronzes.
Donna Arnold 1 , Andrei Rotaru 1 , Finlay Morrison 1
1 School of Chemistry, University of St Andrews, St Andrews United Kingdom
Show AbstractThe combination of the requirement for Pb-free replacements for PbZr
xTi
1-xO3 (PZT) [1] and the recent renaissance in multiferroics [2] has re-invigorated the investigation of ferroelectric systems. To date the main focus has been on perovskite (ABO
3) based materials such as K
1-xNa
xNbO
3 (as a Pb-free piezoelectric [3]) and BiFeO
3 (the most well-known room temperature multiferroic [4]) due to both their compositional flexibility and also our level of understanding of mechanisms to tune properties in this structure type; simple arguments based on steric considerations (tolerance factor), cation and charge ordering and octahedral tilting are all tools to be exploited in the quest for new perovskite ferroelectric and multiferroic materials.
The tetragonal tungsten bronze (TTB) structure, A
2A′
4B
2B′
8O
30, is closely related to the perovskite structure and offers a similar degree of compositional flexibility, however the presence of crystallographically non-equivalent A- and B-sites provides an extra degree of freedom for manipulation of the structure. Although ferroelectric TTBs (including Ba
2NaNb
5O
15 and (Ba,Sr)Nb
2O
6) were widely studied in the 1960’s-70’s our understanding of manipulation of this structure-type is poor compared to perovskites.
Our work is currently investigating relaxor TTB materials based on A
6MNb
9O
30 (where A = Ba
2+, Sr
2+, Ca
2+ and M = Ga
3+, Sc
3+, In
3+ and Y
3+) with a view to understanding composition-structure-property inter-relations. We discuss anisotropy and cation size variance effects [5] in these materials and their correlation with dielectric relaxor properties. The ultimate aim is to use these relationships to guide development of novel ferroelectric and multiferroic materials.
1. T. R. Shrout, S. J. Zhang,
J. Electroceram. 19, 111 (2007)
2. N. A. Spaldin, M. Fiebig,
Science,
309, 391 (2005)
3. Y. Salto et al.,
Nature,
432, 84 (2004)
4. G. Catalan, J.F. Scott,
Adv. Mat.,
21, 1 (2009)
5. J.P. Attfield,
Chem. Mater.,
10, 3239 (1998)
3:45 PM - F11.4
Growth and Characterization of Tetragonal Bi(Zn1/2Ti1/2)O3-BiFeO3 Films with Giant Tetragonality.
Keisuke Yazawa 1 , Shintaro Yasui 1 , Masaaki Matsushima 1 , Hiroshi Uchida 2 , Takashi Iijima 3 , Tomoaki Yamada 1 , Hiroshi Funakubo 1
1 Innovative and Engineered Materials, Tokyo Instiute of Technolory, Yokohama, Kanagawa, Japan, 2 Materials and Life Sciences, Sophia University, Chiyoda-ku, Tokyo, Japan, 3 Reserch Center for Hydrogen Industrial Use and Strage, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki, Japan
Show AbstractRecently, some ferroelectric materials with large tetragonality have been reported especially by high pressure synthesis [1,2], and the large ferroelectricity beyond 150 μC/cm2 is expected from the crystal structure. Among them, Bi(Zn1/2Ti1/2)O3 prepared under high pressure condition has tetragonal perovskite-type structure with large c/a of 1.211 and the calculated spontaneous polarization value of 158 μC/cm2 [2]. In addition, the enhancement of tetragonality of PbTiO3 was reported by the solid solution with BiFeO3 [3], which expect to accelerate the ferrroelectrricity. Therefore, we tried to enhance the tetragonality by making the solid solution of Bi(Zn1/2Ti1/2)O3-BiFeO3. To stabilize this phase synthesized at high pressure, we employed epitaxial films because we succeed to stabilize high pressure perovskite SrIrO3 phase as epitaxial films [4]. In this study, Bi(Zn1/2Ti1/2)O3-BiFeO3 films were grown on (100)cSrRuO3 // (100)SrTiO3 substrates by metalorganic chemical vapor deposition at 770oC. The films composition was determined by X-ray fluorescence. The crystal structure was characterized by high-resolution X-ray diffraction analysis. The microstructure of the films was observed by using cross-section TEM image. Piezoelectric force microscopy was used to confirm switching ferroelectric domains. Epitaxial films with pure tetragonal perovskite-type structure with (100)/(001)-orientation was successfully grown. 93% of (001) orientation was achieved and its tetragonality was found to be 1.221, which was larger than the reported value for Bi(Zn1/2Ti1/2)O3. Moreover, the tilting angle of a-domain was 10o which was larger that the reported value for PbTiO3 (about 2.5-3.6o [5]). In addition, the twin boundary with [101] plain tilted about 50o from substrate surface was observed from the cross-section TEM image. This large tilting angle can be explained by the large tetragonality as well as the large tilting angle of a-domain. Furthermore, polarization reversal by electric field was ascertained by using piezoelectric force microscopy. From these results, we successfully prepared the giant tetragonality-distorted epitaxial films which were implied having huge ferroelectricity. [1] A. A. Belik, M. Azuma, T. Saito, Y. Shimakawa, M. Takano, Chem. Mater. 17 (2005) 269.[2] M. R. Suchomel, A. M. Fogg, M. Allix, H. Niu, J. B. Claridge, M. J. Rosseinsky, Chem. Mater. 18 (2006) 4987.[3] V. V. S. S. Sai Sunder, A. Halliyal, A. M. Umarji, J. Mater. Res. 10 (1995) 1301.[4] Y. K. Kim, A. Sumi, K. Takahashi, S. Yokoyama, S. Ito, T. Watanabe, K. Akiyama, S. Kaneko, K. Saito, H. Funakubo. Jpn. J. Appl. Phys. 45 (2006) L36[5] S. Utsugi, T. Fujisawa, R. Ikariyama, S. Yasui, H. Nakaki, T. Yamada, M. Ishikawa, M. Matsushima, H. Morioka, H. Funakubo, Appl. Phys. Lett. 94 (2009) 052906.
4:00 PM - F11: Structure
Break
4:15 PM - F11.5
Universal Behavior in Structural and Ferroelectric Properties for RE-substituted BiFeO3 Thin Films.
Daisuke Kan 1 , Lucia Palova 2 , Vartharajan Anbusathaiah 3 , Ching Cheng 3 , Shigehiro Fujino 1 , Valanoor Nagarajan 3 , Karin Rabe 2 , Ichiro Takeuchi 1
1 , University of Maryland, College Park, Maryland, United States, 2 , Rutgers University, Piscataway, New Jersey, United States, 3 , University of New South Wales, Sydney, New South Wales, Australia
Show AbstractWe have recently discovered substantial enhancement in dielectric/ferroelectric/piezoelectric properties at a rhombohedral to pseudo-orthorhombic structural boundary in (Bi,Sm)FeO3.[1] In this study, we have performed systematic investigations on structural and ferroelectric properties of BiFeO3 doped with rare-earth (RE) elements Sm, Gd, Dy in a combinatorial manner. Thin film composition spreads of (Bi,RE)FeO3 were fabricated by combinatorial pulsed laser deposition on SrTiO3 (100) substrates with SrRuO3 buffer layers. Scanning x-ray diffraction reveals that a rhombohedral to a orthorhombic structural transitions are universally observed for all RE elements studied here and that the structural properties can be described as a function of average ionic radius of A-site. This indicates that the primary cause of the transition is the chemical pressure effect due to the substitutions. We also found that, at the transition boundary, a single ferroelectric hysteresis loop on the undoped BiFeO3 side undergoes a transition to a double hysteresis loop, with an enhancement of dielectric constant ε33 and piezoelectric coefficient d33. In this presentation, we will also discuss the possible origin of the double hysteresis loop based on results from the first principles calculations. This work is supported by DMR 0520471, NSF DMR 0603644, ARO W911NF-07-1-0410 and the W. M. Keck Foundation.[1] S. Fujino, M. Murakami, V. Anbusathaiah, S.-H. Lim, V. Nagarajan, C. J. Fennie, M. Wuttig, L. Salamanca-Riba, and I. Takeuchi Appl. Phys. Lett. 92, 202904 (2008).
4:30 PM - **F11.6
First-principles and Experimental Studies on Ferroelectrics and Relaxors.
Ronald Cohen 1
1 Geophysical Laboratory, Carnegie Institution of Washington, Washington, District of Columbia, United States
Show AbstractTheory and experiments on pure PbTiO3 under pressure show that amorphotropic phase boundary (MPB) exists in pure PbTiO3 underpressure, and that the high coupling materials including PZT andPMN-PT simply tune this transition to room pressure chemically. Usingthis idea of chemical pressure, we are searching for new high couplingpiezoelectrics. It would be useful to have strong coupling materialsthat (1) work to higher temperatures (have higher Tc or TR-T), (2)have higher coercive fields, and (3) are pure compounds that meltcongruently. Two candidates we have been studying are (Pb,Sn)TiO3 and(Pb,Sn)ZrO3 We find these material to have an orthorhombic ormonoclinic ground states, and a higher energy tetragonal phase withlarge c/a strain. The energy difference is very small, so that thepolarization can be easily rotated, which suggests very strongpiezoelectric constants. Other new materials will also be discussed.A key question is whether relaxor behavior in relaxor ferroelectricsis significant to the origin of high electromechanical coupling.Simulations show that the most probable cause for relaxor behavior inPMN-type relaxors is from polar nanoregions (PNR) that form inchemically ordered regions (COR), and that PNR form around COR. Thissuggests that the large coupling and presence of MPB are separate fromthe relaxor behavior. We have experimentally studied X-ray diffusescattering in PSN as a function of pressure and temperature. Moleculardynamics with a first-principles based effective Hamiltonian gives theobserved anisotropic diffuse X-ray scattering, and the origin of thescattering will be discussed. Finally, new experiments onhigh-pressure ferroelectricity will be discussed.
5:00 PM - F11.7
Effect of High-pressure on Multiferroic BiFeO3.
Jens Kreisel 1 , R. Haumont 2 , P. Bouvier 1 , B. Dkhil 4 , A. Pashkin 3 , C. Kuntscher 3
1 , CNRS, Grenoble Institute of Technology, Grenoble France, 2 ICCMO, Orsay University, Oarsay France, 4 SPMS, Ecole Centrale Paris, Paris France, 3 Physics, Augsburg University, Augsburg Germany
Show AbstractMultiferroics, also called “ferroelectromagnets”, are known for long time as materials exhibiting at least both magnetic and polar order. Among them, BiFeO3 is the most studied and promising candidate, considered as a holy grail, as it exhibits “robust” multiferroic properties with coexistence of both antiferromagnetic (TN = 352°C-370°C) and ferroelectric (TC = 810°C-830°C) orders [1]. Whereas BiFeO3 is intensively studied and used especially as thin film for applications goals, works on its bulk pressure-stability are rather scare, and some controversies remains on the crystallographic structure especially at high temperature. Here we focus on our recent pressure-dependent investigation of the multiferroic perovskite bismuth ferrite BiFeO3 (BFO) by using synchrotron X-ray powder diffraction together with IR spectroscopy and optical birefringence.Our pressure-dependent IR and X-ray scattering study reveals that BFO presents significant pressure-instabilities in agreement with recent theoretical predictions [2]. A first structural phase transition occurs as low as 3 GPa towards a distorted monoclinic perovskite structure which is characterized by the superimposition of tilts and cation displacements. With further increasing pressure the cation displacements of BiFeO3 are reduced and finally suppressed around 10 GPa leading to the non-polar Pnma structure in agreement with recent [3] theoretical ab-initio predictions (that have not predicted the occurrence of the intermediate phase). Contrary to earlier experimental and theoretical investigations of BFO where no low-pressure structural phase transition was reported, our study thus provides evidence that BFO presents further structural instabilities below 15 GPa It appears that a complex competition between the oxygen octahedra tilting and the polar character especially through the Bi lone pair electron conditions the intermediate monoclinic phase, which we believe to be a general feature for Bi-based perovskite compounds.[1] G. Catalan and J. F. Scott, Advanced Materials 21, 1 (2009).[2] R. Haumont, P. Bouvier, A. Pashkin, K. Rabia, S. Frank, B. Dkhil, W. A. Crichton, C. A. Kuntscher, and J. Kreisel, Physical Review B 79, 184110 (2009).[3] P. Ravindran, R. Vidya, A. Kjekshus, H. Fjellvåg, and O. Eriksson, Physical Review B 74, 224412 (2006).
5:15 PM - F11.8
High Temperature Phase Transitions in BiFeO3.
Donna Arnold 1 , Philip Lightfoot 1 , Finlay Morrison 1
1 School of Chemistry, University of St Andrews, St Andrews, Fife, United Kingdom
Show AbstractMultiferroics represent an important technological class of materials which simultaneously exhibit magnetic and ferroelectric ordering; of particular interest is BiFeO3(BFO) which exhibits both room temperature antiferromagnetic ordering (TN ~ 350-370 °C) and ferroelectric ordering (TC ~ 810-830 °C).[1] Whilst many authors have investigated the crystal structure of BFO the structural phase transitions are still not well known. Two high temperature phase transitions have been reported, namely α-BFO (ferroelectric) – β-BFO (paraelectric) at approximately 820 °C and a β-BFO to γ-BFO phase transition at approximately 930 °C. Whilst it is widely accepted that the α-phase crystallises in the rhombohedral R3c space group various symmetries including orthorhombic, rhombohedral and monoclinic symmetries have been reported for the β-phase. The γ-phase has been investigated to a lesser extent primarily due to the instability of BFO at high temperatures although some authors have postulated that this phase is cubic in nature.[2] This latter phase transition (i.e β-γ) is also reportedly coupled with an insulator-metal transition.[2] In this paper we report unambiguous powder neutron diffraction (PND) data which confirms the β-phase to be orthorhombic with a space group Pbnm and a full crystallographic model is proposed.[3] We also show the evolution of the paraelectric β-phase through time-resolved PND studies and demonstrate the phase transition occurs as a first order transition with co-existence of both the rhombohedral α- and the orthorhombic β-phases at temperatures between 820 °C and 830 °C. Moreover we demonstrate that no symmetry change is observed at the insulator-metal transition with both the β-BFO and γ-BFO phases exhibiting orthorhombic symmetry similar in nature to the metal-insulator transitions observed in perovskite nickelates.[4] We will also attempt to shed light on the postulated ‘Polomska’ transition proposed at ~ 180 °C.[5][1] W. Kaczmarek, Z. Pajak, Solid State Commun., 1975, 17, 807[2] R. Palai, R. S. Katiyar, H. Schmid, P. Tissot, S. J. Clark, J. Robertson, S. A. T. Redfern, J. F. Scott, Phys. Rev. B., 2008, 77, 014110[3] D. C. Arnold, K. S. Knight, F. D. Morrison, P. Lightfoot, Phys. Rev. Lett., 2009, 102, 027602[4] J. L. Garcí-Muñoz, J. Rodríguez-Carvajal, P. Lacorre, J. B. Torrance, Phys. Rev. B., 1992, 46, 4414[5] M. Polomska, W. Kaczmarek, Z. Pajak, Phys. Status Solidi A, 1974, 23, 567
5:30 PM - F11.9
Geometry and Size Effects on the Domain Polarization and Switching Dynamics of BiFeO3 Thin Film-based Nanocapacitors.
Ramesh Nath 1 4 , Jeffrey Klug 1 5 , Alexandra Imre 2 , Bernd Kabius 3 , Seungbum Hong 1 , Michael Bedzyk 6 5 , Ram Katiyar 4 , Orlando Auciello 1 2
1 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States, 4 Institute of Functional Materials, University of Puerto Rico, San Juan, Puerto Rico, United States, 5 Physics and Astronomy, Northwestern University, Evanston, Illinois, United States, 2 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, United States, 3 Electron Microscopy Center, Argonne National Laboratory, Argonne, Illinois, United States, 6 Materials Science and Engineering, Northwestern University, Evanston, Illinois, United States
Show AbstractWith its robust ferroelectric state (high polarization and Curie temperature), BiFeO3 (BFO) is a strong candidate material for application to the next generation of high-density non-volatile ferroelectric random access memories (FeRAMS), where it is imperative to reduce the size of the ferroelectric capacitors without losing polarization or thermal stability. In our previous work, PFM studies of square and round shaped BFO nanocapacitors revealed a shape dependence on the ferroelectric domain configuration, where square-shaped nanostructures exhibit a single variant polarization domain configuration, whereas round-shaped nanostructures exhibit seven variants of domain configuration. Moreover, local d33 piezoelectric coefficient measurements showed hysteresis loops with a strong displacement in the voltage axis (strong imprint) for the square-shaped nanostructures, while the round-shaped ones exhibited more symmetric loops. However, these early results may have been influenced by ion-induced damage incurred during fabrication of the nanocapacitors via focused ion beam (FIB)-induced sputtering of material around the defined capacitor. In this respect, the work reported here has been directed at the growth and fabrication of BFO thin film-based nanostructures with limited or no damage, using also the FIB fabrication technique, and characterization of the polarization domain and switching dynamics. In the work presented here, the polarization domain and switching dynamics of BFO nanocapacitors of various geometries (square, rectangular, and circular) and sizes have been studied using Piezoresponse Force Microscopy (PFM), Transmission Electron Microscopy (TEM), and electrical measurements. The nanocapacitors were fabricated using a top-down approach with the combination of electron beam lithography and focused-ion beam (FIB) technique to pattern defect-free structures as small as 100 nm. The 2-step patterning process was carried out on a sample with a 40 nm epitaxial BFO film grown by magnetron sputter-deposition on single crystal SrTiO3 (001) substrates and SrRuO3 (SRO) as the bottom electrode. Capacitors with sizes ranging from 500 nm to 200 nm, varying shapes (e.g. symmetry, aspect ratio) and orientation (relative to the film in-plane crystallographic axes) were fabricated. We will present results of PFM, cross-sectional TEM, and conventional electrical characterization. Size, shape, and orientation dependence of piezoelectric properties, domain behavior, and device performance will be discussed. This work was supported by US Department of Energy, Office of Science, Office of Basic Energy Sciences-Materials Science, under contract DE-AC02. The Use of the Center for Nanoscale Materials was supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.