9:00 PM - C3.20
Fabrication of Ferroelectric BLT Thin Films By Direct Liquid Injection MOVCD.
Marco Lisker 1 , Chia-Pin Yeh 1 , Tomas Grinys 1 , Edmund Burte 1
1 IMOS, University of Magdeburg, Magdeburg, Saxony Anhalt, Germany
Show AbstractFerroelectric lead-free bismuth titanate Bi4Ti3O12 (BTO) has a great potential for applications such as nonvolatile memories, piezoelectric and electro-optic devices. The ferroelectric BTO consists of perovskite Bi2Ti3O10 block sandwiched between two consecutive fluorite-like (Bi2O2)2+ layers. In spite of the advantageous relatively high remanent polarization (2Pr=8–40 μC/cm2) of BTO films, poor fatigue resistance as well as high leakage current density limits their practical applications. The partial substitution of volatile Bi3+ by La3+ ions improves chemical stability of oxygen ions in the perovskite block. Therefore lanthanum substituted bismuth titanate Bi4-xLaxTi3O12 (BLT) where 0.5
9:00 PM - C3.21
Crystal Structure and Electric Properties of Epitaxial MOCVD- Bi(Fe, Co)O3 Films Having Crystal Symmetry Change with Composition.
Hiroshi Funakubo 1 , Shintaro Yasui 1 , Hiroshi Naganuma 2 , Soichiro Okamura 2 , Ken Nishida 3 , Takashi Yamamoto 3 , Takashi Iijima 4 , Masaki Azuma 5 , Hitoshi Morioka 6 , Keisuke Saito 6
1 , Tokyo Institute of Technology, Yokohama Japan, 2 , Tokyo University of Science, Tokyo Japan, 3 , National Defense Academy, Yokosuka Japan, 4 , National Institute of Advance Industrial Science and Technology, Tsukuba Japan, 5 , Kyoto University, Kyoto Japan, 6 , Bruker AXS, Yokohama Japan
Show AbstractOne of the concept of the coexistence of the ferroelectric and ferromagnetic properties is the coupling of these two properties through the mechanical strain, such as a composite of the materials having ferroelectricity and ferromagnecity. In this case, large strain induced by the electric field or magnetic field is one of a key issue. Based on this idea, large piezoresponse possible to induce the large magnetic response by the electric field even in a single material We proposed BiFeO3-BiCoO3 solid solution system having a crystal symmetry change with composition, like Pb(Zr,Ti)O3, as a candidate system for large piezoelectric response. Epitaxial films with 200 nm in thickness were prepared by metalorganic chemical vapor deposition (MOCVD). The crystallographic analysis clarified that the crystal symmetry changes from rhombohedral to tetragonal with increasing the BiCoO3 content [1], suggesting the large piezorespose at this phase boundary as well as the ferromagnetisity. In the present study, the crystal structure changed with the film thickness and the BiCoO3 content were systematically investigated. Furthermore, the electrical properties of these films were also evaluated.(001)-oriented epitaxial (1-x) BiFeO3-xBiCoO3 films were grown on (100)cSrRuO3//(100)SrTiO3 substrates by MOCVD. Crystal symmetry was changed with increasing BiCoO3 content as follows; rhombohedral, rhombohedral-tetragonal, tetragonal. The mixture region with rhombohedral-tetragonal became narrowing in BiCoO3 content with increasing the film thickness. Well-saturated P - E hysteresis loops were ascertained at 80 K from x = 0 - 0.22. The details of the relationships between the crystal structure and electrical property are discussed as well as magnetic property.[1] S. Yasui et al., Jpn. J. Appl. Phys. 46 (2007) 6948.
9:00 PM - C3.22
Deposition of Ir/PZT/Ir Thin Films on Three-dimensional Trench Structure for Ferroelectric Random Access Memory Application.
Marco Lisker 1 , Chia-Pin Yeh 1 , Serhiy Matichyn 1 , Edmund Burte 1
1 IMOS, University of Magdeburg, Magdeburg, Saxony Anhalt, Germany
Show AbstractFerroelectric non-volatile memories have the potential to replace non-volatile memories such as floating and flash-erasable programmable read-only memories (EEPROMs), because of their lower writing voltages, faster writing speeds, better endurance, and potentially fewer processing steps. PZT ferroelectric films are intensively studied worldwide as promising candidates for non-volatile memory applications due to large remnant polarization, low-leakage conduction and relatively low-temperature deposition process.In particular, the development of low-temperature thin film fabrication techniques is one of the most important key issues. Low-temperature growth of ferroelectric thin films can prevent the degradation of ferroelectric/metal/semiconductor interfaces or ferroelectric/insulator/ semiconductor interfaces caused by thermal damage and mutual diffusion. In order to deposit PZT films, various techniques have been used, such as laser ablation, sputtering, sol–gel, metal-organic decomposition and metalorganic chemical vapor deposition.Among them, Metal-organic chemical vapor deposition (MOCVD) is one of the most useful growth technique used for ferroelectric thin films because it gives good step coverage, good uniformity on a large area and a good film quality can be obtained. Unlike conventional CVD, PZT MOCVD has a fundamental problem in that stable delivery of precursors is hard to achieve with conventional bubbler technology. Volatility of precursors can be enhanced by elevating the temperature of the delivery system to about 200° C. However precursors tend to degrade gradually at an elevated temperature for extended periods, rendering them non-volatile. Furthermore, the vapor pressure in the bubbler varies with time, so that constant delivery is hard to achieve. In order to overcome the limitation of precursors, liquid delivery was suggested and exhibited promising results.Lead-zirconate-titanate films were prepared on three-dimensional (aspect ratio 2 – 4) Ir/TiN/SiO2/Si substrates using liquid delivery metalorganic chemical vapor deposition (LD-MOCVD).As-deposited films were already polycrystalline but a post-deposition annealing step increased the phase transformation to the perovskite phase. Annealing at 600° C and higher temperatures leads to a significant loss of the lead in the annealed films. The content of lead was lower as necessary to stabilize the perovskite structure; the pyrochlore phase began to appear. PZT films annealed at 570° C showed a saturated hysteresis loop with a remnant polarization 2Pr of ~ 30 μC/cm2 and a coercive field of 80 kV/cm.
9:00 PM - C3.23
Synthesis and Characterization of New Multiferroic Complex Oxides Thin Films.
Riad Nechache 1 , Catalin Harnagea 1 , Mangala P. Singh 2 , Lina Gunawan 3 , Patrick Fournier 2 , Gianluigi A. Botton 3 , Alain Pignolet 1
1 Energie, Materiaux et Telecommunications (EMT), Institut Nationale de la Recherche Scientifique (INRS), Varennes, Quebec, Canada, 2 Département de Physique, Université de Sherbrooke, Sherbrooke, Quebec, Canada, 3 Materials Science and Engineering Brockhouse Institute , McMaster University, Hamilton, Ontario, Canada
Show Abstract9:00 PM - C3.24
Dielectric and Magnetic Properties of Mn-doped Potassium Tantalate Ceramics.
Paula Vilarinho 1 , Alexander Tkach 1 2 , Abílio Almeida 2 , Subhankar Bedanta 3 , Pavel Borisov 3 , Vladimir Shvartsman 3 , Wolfgang Kleemann 3
1 Department of Ceramics and Glass Engineering, University of Aveiro, Aveiro Portugal, 2 Department of Physics of Science Faculty, University of Porto, Porto Portugal, 3 Angewandte Physik, Universität Duisburg-Essen, Duisburg Germany
Show Abstract(Ba,Sr)TiO3 is currently considered as the main candidate for tunable dielectric applications due to the high tunability of the dielectric permittivity of the ferroelectric BaTiO3 and low dielectric losses of the quantum paraelectric SrTiO3. However, KTaO3 (KT) possesses even lower dielectric losses than SrTiO3, and high room-temperature dielectric tunability can be obtained in KT-based materials by doping. A ferroelectric phase transition was observed in KT with isovalent substitutions of K+ or Ta5+ by off-center Li+ or Nb5+ ions, respectively [1]. On the other hand, a dielectric anomaly can be induced also by heterovalent dopants such as Mn2+ on the K site [2]. Interesting is that doping KT with Mn may induce magnetic properties, making this system attractive for possible multiferroic functional applications, where both capacitance and inductance can be controlled by magnetic or electric fields, respectively.In this work dielectric spectroscopy and SQUID magnetometry techniques are used to study the effect of Mn doping on the properties of KT ceramics. A pronounced frequency-dependent peak in temperature dependence of the dielectric permittivity, accompanied by a peak in the temperature dependence of the dielectric losses, is revealed around 65 K in KT doped by 3 at.% of Mn. The origin of this dielectric anomaly is attributed to displacement of Mn2+ from the center of the K+ site in one of the six <001>-type directions. The relaxation rate of the formed dipoles can be described by an Arrhenius law with an activation energy U = 0.109 eV, which is close to the value obtained for Mn-doped KT single crystals [2]. On the other hand, fitting to the power law with the glass temperature Tg = 32.4 ± 1.5 K, and the dynamical critical exponent zν = 9.67 ± 0.45 is also applicable to the obtained data. Furthermore, the temperature dependence of the magnetization mZFC-FH(T) of Mn-doped KT ceramics shows a spin-glass-like anomaly around 38 K and “memory” effect below this temperature, implying that Mn-doped KT refers to a “multiglass” system similarly as the recently discovered Mn-doped SrTiO3 one [3].References[1]B.E. Vugmeister and M.D. Glinchuk (1990) Rev. Mod. Phys. 62, 993[2]V.V. Laguta, M.D. Glinchuk, I.P. Bykov, J. Rosa, L. Jastrabik, M. Savinov, Z. Trybula (2000) Phys. Rev. B 61, 3897[3] W. Kleemann, V. V. Shvartsman, S. Bedanta, P. Borisov, A. Tkach, P. M. Vilarinho, (Sr,Mn)TiO3 - a magnetoelectrically coupled multiglass (2008) J. Phys.: Condens. Matter (in print)
9:00 PM - C3.25
Ferroelectric Properties of Pb(Zr,Ti)O3 Thin Films on GaN/c-sapphire and STO: Nb Substrates Grown by rf Magnetron Sputtering.
Bo Xiao 1 , Vitaliy Avrutin 1 , Umit Ozgur 1 , Huiyong Liu 1 , Xiaojin Wang 2 , David Smith 2 , Hadis Morkoc 1
1 Electrical Engineering, Virginia Commonwealth University, Richmond, Virginia, United States, 2 Physics, Arizona State University, Tempe, Arizona, United States
Show Abstract9:00 PM - C3.26
Atomic Layer Deposition of Barium Titanate and Barium Strontium Titanate for FeRAM Application.
Rajesh Katamreddy 1 , Vincent Omarjee 1 , Benjamin Feist 1 , Christian Dussarrat 1
1 , Air Liquide Inc, Newark, Delaware, United States
Show AbstractPerovskite-based oxides material such as barium titanate (BTO) or barium strontium titanate (BST) are promising ferroelectric materials for non-volatile memory application. Ferroelectric perovskites exhibit a spontaneous electric polarization that can be reoriented by an external electric field. Atomic layer deposition (ALD) is the preferred method for depositing multimetallic oxide thin films especially where precise control of film composition and structure are highly desired. This is even more critical for ferroelectric application as the properties of the device are highly dependent on the film composition and structure. For example, BaTiO3 and BaTi2O5 are the known ferroelectric materials among oxide of barium and titanium. Excellent film uniformity and conformality is also achieved using ALD technique. For successful ALD of BTO and BST, the selection of appropriate Ba, Ti and Sr precursors is critical. Final choice of precursors will depend on Ba, Sr and Ti precursors’ process compatibility but also on the performance of the resulting films for the ferroelectric application. In this work, we study the compatibility of strontium precursors, AbsolutSrTM and HyperSrTM, analogous barium precursors AbsolutBaTM and HyperBaTM, and various Ti precursors for ALD of BTO and BST. Novel Ti precursors studied include PrimeTiTM, StarTiTM and TyALDTM. BTO and BST films deposited using the most compatible precursors are chemically and electrically characterized for FeRAM application. The ferroelectric behavior of the BTO and BST materials are also highly dependent on the crystal structure. Barium titanate has five phases: hexagonal, cubic, tetragonal, orthorhombic, and rhombohedral and only cubic does not display ferroelectric effect. The effect of temperature on crystal structure is studied by performing X-ray diffraction measurements of films annealed at different temperatures.
9:00 PM - C3.27
Dielectric and Magnetic Properties of BiFe1-xNdxO3 and BiFe0.95Li0.05O3.
Ricardo Melgarejo 1 , Nishit Murari 1 , Jose Saavedra-Arias 1 , Reji Thomas 1 , Ram Katiyar 1
1 Depatment of Physics and Institute of Functional Nanomaterials, University of PuertoRico, San Juan, Puerto Rico, United States
Show AbstractMultiferroic materials have recently seen a surge of research activities due to its applications in nonvolatile memories, spintronics, sensors, and micro mechanical systems (MEMS). BiFeO3 is a naturally occurring multiferroics. However, the large leakage current is a concern for practical applications and substitution at Bi and Fe is commonly employed to circumvent this problem. Here, Fe substitution by Nd and Li is considered for this purpose. Thin films on Pt/Ti/SiO2 /Si were grown by chemical solution deposition (CSD) and characterized for structure and symmetry by XRD and Raman scattering. The XRd and Raman spectra showed well-grown perovskite structure with no phase segregation. Surface morphology is observed by AFM, dielectric properties by impedance analyzer, and the leakage current by I-V measurements. Magnetic (M-H) and electric (P-V) hysteresis loops were also studied. The variation of dielectric constant (er) and loss tangent (tand) with temperature and frequency were systematically studied. The effect of Nd and Li substitution on the electrical properties will be presented.
9:00 PM - C3.28
Single-crystal-like, Epitaxial, Mutiferroic BiFeO3 Thin Films on Single-crystal-like, Biaxially Textured, Flexible Metallic Tapes.
Junsoo Shin 1 , Amit Goyal 1 , Katyayani Seal 1
1 , Oak Ridge National Lab., Oak Ridge, Tennessee, United States
Show AbstractMultiferroic materials have been extensively investigated in the past couple of years because of the coexistence of ferroelectric and magnetic ordering. BiFeO3 (BFO) is one of a few naturally existing multiferroic materials. In bulk form, BFO exhibits a rhombohedrally distorted perovskite structure with space group R3c, with a polarization along the (111) direction and antiferromagnetic ordering of Fe3+. Recently, several groups have reported three different oriented BFO thin films such as (001), (101), and (111) phases successfully fabricated on (001), (101), and (111) SrTiO3 single crystal substrates, respectively, each of which exhibits different remanent polarizations. Here, we have explored the control of differently oriented, epitaxial BFO thin films, by appropriate selection of epitaxial buffer layers grown on (001) textured, single-crystal-like flexible metallic tapes via pulsed laser deposition. By selecting some buffer layers, BFO thin films on Ni-W substrates have a single (001) phase. Other choices of buffer layers provide BFO thin films to the predominant (110) or (111) orientation with weak (001) phase. The structure and phase of the films were characterized by x-ray diffraction. The ferroelectricity of each film was analyzed and compared by macroscopic and nanoscale measurements using a ferroelectric tester and switching spectroscopy piezoresponse force microscopy (SSPFM). Interestingly, nanoscale piezoresponse SSPFM mapping of BFO thin films on Ni-W substrates indicates no significant reduced ferroelectricity at the grain boundary (defined as a misfit angle less than 5°), which implies the quality of ferroelectricity in epitaxial BFO thin films grown on polycrystalline, single-crystal-like, Ni-W tapes is similar to that of thin films on single crystal substrate. The success of this work suggests that oriented-controllable BFO thin films on flexible substrates should enable broad applications in flexible mutiferroic devices without limitation on size and expensive cost for substrates. JS would like to thank S.V. Kalinin and S. Jesse for discussion on SSPFM measurement. Research sponsored by the LDRD Program of ORNL, managed by UT-Battelle, LLC for the U. S. Department of Energy. A portion (PFM and SSPFM) of this research was performed at ORNL’s CNMS, sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy.
9:00 PM - C3.29
Growth of Self-assembled CoFe2O4-BiFeO3 Thin Films by Pulsed Laser Deposition.
Sandra Dussan-Devia 1 , Manoj Singh 1 , G. Sharma 1 , Ram Katiyar 1
1 Physics, University of Puerto Rico, Rio Piedras Campus, San Juan, Puerto Rico, United States
Show Abstract9:00 PM - C3.3
Characteristics of Ba0.48Sr0.52TiO3/LaNiO3 Artificial Superlattices Prepared by rf Magnetron Sputtering.
Hsin-Yi Lee 1 , Kun-Fu Wu 2 , Heng-Jui Liu 1 , Chih-Hao Lee 2
1 Research Division, National Synchrotron Radiation Research Center, Hsinchu Taiwan, 2 Department of Engineering and system science, National Tsing Hua University, Hsinchu Taiwan
Show AbstractArtificial superlattices consisting of ferroelectric Ba0.48Sr0.52TiO3 (BST) and conductive LaNiO3 (LNO) sublayers were epitaxial grown on SrTiO3 (001) single crystal substrates by a RF magnetron sputtering system. X-ray reflectivity and high-resolution diffraction measurements were employed to characterize the microstructure of these films. Formation of a superlattice structure was confirmed from the appearance of Bragg peaks separated by Kiessig fringes in x-ray reflectivity curves and a diffraction pattern. The clearly discernible main feature and satellite features on both sides of the substrate about the (002) SrTiO3 Bragg peak indicate the high quality of the BST/LNO artificial superlattice structure formed on a SrTiO3 substrate. The mean c-axis parameter of superlattices is larger than the weighted mean of unstrained BST and LNO single-phase films showing an elongation of the c-axis lattice of the superlattice. These BST/LNO artificial superlattices show a significant enhancement of dielectric constant with small dielectric loss relative to BST single layers of the same thickness.
9:00 PM - C3.30
Deposition and Characterization of Low-pressure Metal-organic Chemical Vapor Deposited Epitaxial BiFeO3 Thin Films.
Manish Singh 1 , Yi Yang 1 , Christos Takoudis 2
1 Chemical Engineerin, University of Illinois at Chicago, Chicago, Illinois, United States, 2 Departments of Chemical and Bioengineering, University of Illinois at Chicago, Chicago, Illinois, United States
Show Abstract9:00 PM - C3.31
Oxide Heterogrowth on Exfoliated Thin-Film Complex-Oxide Substrates.
Tsung-Liang Chen 1 , Angela Kou 2 , Avishai Ofan 3 , Ophir Gaathon 3 , Oleg Gang 4 , Lakshmanan Vanamurthy 5 , Sasha Bakhru 5 , Hassaram Bakhru 5 , Richard Osgood 1 3
1 Department of Electrical Engineering, Columbia University, New York, New York, United States, 2 Department of Physics, Columbia University, New York, New York, United States, 3 Department of Appied Physics and Applied Mathematics, Columbia University, New York, New York, United States, 4 , Brookhaven National Laboratory, Upton, New York, United States, 5 College of Nanoscale Science and Engineering, State University of New York at Albany, Albany, New York, United States
Show AbstractIon exfoliation using deep-ion implantation induced chemistry has been widely used as a means for fabrication of thin fully single-crystal complex-oxide films. These films can be utilized as a platform for more complex optical or electronic devices or for substrates for additional epitaxial or advanced growth. In this talk, we will discuss our successful demonstration of growth of a thin layer of HfO2 by atomic layer deposition (ALD) onto a 10-μm-thick He+ implanted lithium niobium film, followed by exfoliation of the bilayer film; in addition growth onto a free-standing 10-μm-thick film has also been demonstrate. Growth is achieved by working within temperature windows for both processes. The surface, film thickness, growth rates and optical properties of the low-temperature-grown HfO2 film are investigated using atomic force microscopy (AFM), scanning electron microscopy (SEM), Rutherford backscattering spectroscopy (RBS), energy dispersive x-ray spectroscopy (EDX) and spectroscopic ellipsometry. In addition, patterned of the grown HfO2 film has been achieved on a pre-implanted LiNbO3 substrate, thus providing a platform for surface material tuning or for fabricating a multilevel oxide integrated structure for future applications. In addition, we demonstrate precise tuning of the surface optical index using a strip-loaded HfO2/LiNbO3 waveguide using index tuning provided by the material system. The application to other oxide-growth methods such PLD and MBE will be discussed, as well as the applicability of the process for reusable thin-oxide substrates.
9:00 PM - C3.33
Phase Diagram of Sr on Si (100): a First-Principles Study.
Kevin Garrity 1 3 , James Reiner 2 3 , F. Walker 2 3 , C. Ahn 2 3 , S. Ismail-Beigi 2 3
1 Physics, Yale University, New Haven, Connecticut, United States, 3 Center for Research on Interface Structures and Phenomena (CRISP), Yale University, New Haven, Connecticut, United States, 2 Applied Physics, Yale University, New Haven, Connecticut, United States
Show Abstract As transistors continue to get smaller and faster, all of their components must scale down accordingly. In particular, current technology requires a dielectric layer which is only a few angstroms thick. Due to quantum mechanical leakage currents at these thickness, new materials with higher dielectric constants and defect free interfaces with silicon are required in order to continue this scaling process. More generally, the epitaxial integration of complex oxides with semiconductors would allow new devices which take advantage of the wide range of oxide properties, including ferroelectric, ferromagnetic, piezoelectric, and multiferroic behavior. To date, the only known method to grow complex oxides on silicon epitaxially has required 1/2 ML of an alkaline earth metal, usually Sr, to be deposited as a first step. This procedure has been successfully applied to the growth of several crystalline oxides, including possible thin film ferroelectrics like SrTiO3. When the Sr is deposited under normal experimental conditions, transitions from a 2x1 silicon reconstruction to a 2x3 and then to a 1x2 phase are observed. These transitions were thought to be required to achieve good epitaxy, but their origin and significance has not been understood. Using first-principles density functional theory calculations, we examine the growth of sub-monolayer coverages of Sr on Si (100) and explain the unusual phase diagram observed experimentally. In particular, we report on a novel class of low energy 1/6 ML structures which require the replacement of 2/3 of the surface silicon dimers. These new structures explain both the reconstructions seen at 1/6 ML as well as the rotation of the surface silicon dimers which is observed during high-temperature Sr deposition. This model predicts the successful growth of oxides under low-temperature conditions with the same interface structure as in the high-temperature case, but rotated 90 degrees. This low temperature growth path has been experimentally verified and produces epitaxial oxides of the same quality as the high temperature procedure.
9:00 PM - C3.34
Stability Of Defects And Defect Clcusters In Linbo3 From Density Functional Theory And Thermodynamic Calculations.
Haixuan Xu 1 , Donghwa Lee 1 , Jun He 1 , Susan Sinnott 1 , Venkatraman Gopalan 2 , Volkmar Dierolf 3 , Simon Phillpot 1
1 Department of Materials Science and Engineering, University of Florida, Gainesville, Florida, United States, 2 Department of Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania, United States, 3 Department of Physics , Lehigh University, Bethlehem, Pennsylvania, United States
Show AbstractLithium niobate (LiNbO3) is an important ferro-, pyro-, and piezoelectric material with many promising physical properties. Its physical properties are greatly influenced by the concentration of defects; therefore, a fundamental understanding of these defects is of great interest. Electronic structure calculations at the level of density-functional theory, combined with a detailed thermodynamic analysis, are used to calculate the defect formation energies (DFE) of various point defects and defect clusters in LiNbO3. The dominant defects are determined. Under Nb2O5-rich conditions, a cluster consisting of a niobium antisite compensated by four lithium vacancies is predicted to show the lowest DFE. Under the usual condition for melt growth, which is in atmospheric conditions, a Li-deficient composition of congruent melting LiNbO3 is predicted, which is consistent with experimental results. Under Li2O-rich conditions, the lithium Frenkel defect is predicted to be the most stable. This is consistent with the underlying mechanism that vapor transport equilibration method can grow stoichiometric LiNbO3. The effects of temperature and oxygen partial pressure are also explored. This work was supported by the National Science Foundation under Grant Numbers DMR-0602986 and DMR-0303279.
9:00 PM - C3.36
Investigation of Phase Transition Behavior in Bulk (1-x)BiFeO3-xBaTiO3.
Serhiy Leontsev 1 , Richard Eitel 1
1 Chemical and Materials Engineering, University of Kentucky, Lexington, Kentucky, United States
Show AbstractSeveral perovskite bismuth ferrite BiFeO3 based thin films systems have been shown to be multiferroic, simultaneously exhibiting ferroelectric and weak ferromagnetic behavior. However, bulk perovskite BiFeO3 has been difficult to obtain due to presence of secondary phases. Additionally, poor electrical properties typically prevent observation of ferroelectric switching. In the current work, the bulk BiFeO3-xBaTiO3 system has been studied as a potential lead-free multiferroic material. Barium titanate BaTiO3 in solid solution with BiFeO3 is proposed to stabilize the perovskite structure and improve switching behavior. Samples with various content of BaTiO3 were prepared via solid-state route and pure perovskite phase was confirmed by x-ray diffraction. Temperature dependent phase transition behavior was investigated by dynamic scanning calorimetry (DSC) and dielectric constant K(T) measurements. The Curie temperature decreases linearly (-12.2°C/mol% BT) with increasing content of BaTiO3. Additionally, both electric and magnetic hysteresis measurements are reported. Despite low electric conductivity and low dielectric loss, dielectric hysteresis measurements do not indicate ferroelectric behavior. Ferromagnetic measurements confirm the presence of weak ferromagnetic behavior for compositions with x<50 mol% BaTiO3. Specifically, in x=20mol% a ferromagnetic transition around T=218K has been observed and characterized. Continuing work, in modified BaTiO3-BiFeO3 material is hoped to provide improved ferroelectric properties and the promise of true multiferroic behavior.
9:00 PM - C3.37
Thickness Dependence of the Martensitic Transition in Ni2MnGa Shape Memory Alloy Thin Wedges.
Catherine Jenkins 1 2 , Peter Poersch 2 , Tobias Eichhorn 2 , Ramamoorthy Ramesh 1 , Hans-Joachim Elmers 2 , Gerhard Jakob 2
1 Department of Materials Science and Engineering, University of California, Berkeley, Berkeley, California, United States, 2 , Johannes Gutenberg University Mainz, Mainz, RLP, Germany
Show AbstractThe Heusler compound Ni2MnGa is a multiferroic material, coupling ferromagnetism and ferroelasticity through a symmetry operation in the lattice known as twin boundary motion. Both epitaxially clamped films and those released by dissolution of the substrate can undergo this motion, which can be applied for example in magnetic actuators, sonar transducers, and active cantilevers in microvalves. In this work, epitaxial films of Ni2MnGa are shown by temperature dependent x-ray and magnetization measurements to undergo a structural phase transition to the active phase at around 140C. However, in situ optical observations of the sample during heating show a complete loss of the topographic features associated with the tetragonally distorted martensite phase by as low as 75C. This discrepancy is explained by the incomplete transformation through the thickness of the film.To confirm and quantify the thickness dependence of the transition, wedge shaped films were grown so that a range of thicknesses could be achieved under identical deposition conditions. We show the existence of a critical thickness, above which the transition proceeds similarly through the bulk and at the surface of the film and below which clamping effects dominate and cause a shift in the temperature and character of the transformation. The critical thickness will dictate the logistics of integrating the shape memory alloy films in applications where the multiferroic coupling of the structure and the magnetism is a feature of design.
9:00 PM - C3.38
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 Electrical Engineering, The Pennsylvania State University, University Park, Pennsylvania, United States, 3 Computer Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania, United States, 4 Applied Research Laboratory, The Pennsylvania State University, State College, 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) thin films were utilized as the piezoelectric material. Chemical solution deposition was used to prepare PZT 52/48 and lead nickel niobate -PZT films. This paper will compare the properties of films prepared using a conventional 2-methoxyethanol (2-MOE) route with those prepared using methanol and 1-butanol-based precursors. It was found that high quality thin films can be prepared using many different precursor routes. The best properties were achieved with {100}-textured films. For films under a micron in thickness, the dielectric constant varied between 900 and 1500 while the remanent polarization ranged between 21 and 25 μC/cm2 and e31,f from –5 to –9.7 C/m2. These films were then integrated into prototype 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 desired 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 on receive of 66 % has been determined for partially released structures.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 3Kbyte of non-chip SRAM, and 50 MHz resolution time delayed excitation pulse generators.
9:00 PM - C3.4
Non Linear Properties of Dense PIN-PT Ceramics.
Mai Pham Thi 1 , Karima Alilat 1 2 , Hichem Dammak 2 , Laurent Lebrun 3 , Martine Doisy 4
1 , Thales R&T France, Palasiseau France, 2 SPCTS, Ecole Centrale de Paris, Chatenay Malabry France, 3 LGEF, INSA Lyon, Lyon France, 4 , Thales Underwater Systems, Sophia Antipolis France
Show AbstractNonlinear measurements of dense PbIn1/2Nb1/2-37%PT (PIN-PT) piezoceramics, were recorded at 1kHz and at resonance under driven AC electric fields and axial static pressure. Influence of donor or softener (Mg, Nb) and acceptor or hardener (Mn) was investigated. Dependence of the real and imaginary parts of the dielectric constant on electric field was compared with PZT hard ceramics and PMN-PT soft ceramics. The dielectric response was analyzed with the Rayleigh law and indicate the hard character of PIN-PT ceramics. In the other hand, the variation of piezoelectric constant (d33) versus pressure reveals the increasing of d33 up to the pressure Ts before the decreasing due to the depolarization. This behavior was observed for soft materials and attributed to domain wall motion. The mechanical nonlinear behavior of piezoelectric ceramics, characterized by two coefficients (α and β, was measured according to the CENELEC European Standards EN5034-3. The coefficient α quantifies the variation of the mechanical loss, tan δm, versus the mean square strain (S): α=Δ(tan δm)/Δ. α is measured in longitudinal mode on free rods driven at the series resonance frequency, fs, at increasing electric field. The new mechanical nonlinear coefficient β measures the compliance variation. The α and β coefficients of PIN-PT ceramics, 9.5x105 and 4.7x106, are larger than that hard PZT (3.6x104 and 3.5x105). The results are consistent with the capability of PIN-PT to withstand the high axial strain.
9:00 PM - C3.40
Growth of Epitaxial CoFe2O4/PZT Heterostructures and Ferroelectric-ferromagnetic Characterization.
Dev Mukherjee 1 , Tara Dhakal 1 , Robert Hyde 1 , Srikanth Hariharan 1 , Pritish Mukherjee 1 , Sarath Witanachchi 1
1 Department of Physics, University of South Florida, Tampa, Florida, United States
Show AbstractIn this work we report the epitaxial growth of CoFe2O4 (CFO) and Lead Zirconium Titanate (PZT) heterostructures using a dual-laser ablation process. The dual laser ablation process that combines the outputs of excimer (uv) and CO2 (ir) laser pulses provides favorable conditions for epitaxial growth of thin films. These structures have been deposited on both MgO (100) and Nb doped SrTiO3 (100) substrates that have a close lattice match with both CFO and PZT. The conducting SrTiO3:Nb substrates were used as the bottom electrodes in the investigation of the polarization hysteresis of the CFO-PZT structures. CFO has one of the highest magnetostrictive coefficients among ferrites while PZT possesses a high piezoelectric coefficient. The possible coupling between the magnetic moment and the electrical polarization in these structures that is mediated by the interfacial stress is of great interest for multiferroic devices. The epitaxial relationship between the CFO and PZT films are important maximize the elastic interaction at the interface. Epitaxial relationship has been confirmed by the θ-2θ and Φ x-ray diffraction scans. The 0.1o width of the (002) x-ray diffraction peak measured by the rocking-curve method also indicates a high degree of epitaxy. Conventional X-ray diffraction sin2ψ method was used to measure the residual stress of the thin films. The magnetic and electric measurements of these films and the correlation between these measurements and the structural parameters will be presented.
9:00 PM - C3.41
Single Domain Rare-earth Scandate Template for Strain Tuning of Ferroic and Multiferroic Thin Films.
Chad Folkman 1 , Chang-Beom Eom 1 , Rasmi Das 1 , Yanbin Chen 2 , Chris Nelson 2 , Xiaoqing Pan 2
1 Material Science and Engineering, University of Wisconsin, Madison, Wisconsin, United States, 2 Material Science and Engineering, University of Michigan , Ann Arbor, Michigan, United States
Show Abstract Epitaxial functional oxides have generated excitement due to the improvement in properties over their amorphous and polydomain counterparts. Generally, high quality epitaxy becomes unachievable with large lattice strain or misfit between the film and substrate. Widely available substrates like SrTiO3 with single surface-terminated and atomically flat surfaces unfortunately have large mismatches (>1.0%) with most of the ferroelectric and multiferroic oxides like BiFeO3 ap = 3.96Å, BaTiO3 ap = 4.00Å, and PZT(MPB) ap = 4.07Å. For this reason, bulk single crystals of orthorhombic Rare-Earth Scandates (REScO3) have been developed where tuning the lattice constant is executed by changing the RE ion. Lattice parameters of REScO3 decrease with increasing Z in the range Z = 51, LaScO3 ap = 4.05Å to Z=71, LuScO3 ap = 3.89Å. In many cases it is undesirable to fabricate REScO3 into large crystals because of the high temperatures required for growth and the inability to integrate into devices. In this work, we overcome these problems by demonstrating single domain, strain relaxed, template films of various REScO3 including: LaScO3, PrScO3, NdScO3, SmScO3, GdScO3, and DyScO3. Thick (~0.5μm) REScO3 films were deposited on 2° miscut (001) LSAT by pulsed laser deposition and annealed ex-situ over 1000°C improving the crystalline quality to near single crystal level. Chemical mechanical planerization was then utilized to remove surface roughness generated from the high temperature anneal followed by the deposition of a homoepitaxial capping layer. The rocking curve full widths at half maximums were typically less than 0.1°. Attributes important to these templates such as temperature stability and dielectric properties were investigated with high temperature x-ray diffraction and interdigit planar electrodes respectively. The results demonstrate that the REScO3 templates are structurally and electrically similar to the bulk single crystals yet because of their thin film form are more accessible for many strain engineering applications of epitaxial functional oxides.
9:00 PM - C3.42
Growth of Single Crystal CaRuO3 Metallic Oxide Thin Films for Multiferroic Heterostructures.
Danielle Proffit 1 , Ho Won Jang 1 , Sanghan Lee 1 , Chang-Beom Eom 1 , Chris Nelson 3 , Xiaoqing Pan 3 , Mark Rzchowski 2
1 Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States, 3 Materials Science and Engineering, University of Michigan-Ann Arbor, Ann Arbor, Michigan, United States, 2 Physics, University of Wisconsin-Madison, Madison, Wisconsin, United States
Show AbstractProgress in strain engineering and the development of new multiferroic materials requires further development of paramagnetic metallic oxide electrodes with controlled lattice parameters. CaRuO3 is a candidate for the study of magnetically functional films, somewhat analogous to the commonly used SrRuO3. In this work, epitaxial thin films of (110) CaRuO3 were grown on orthorhombic (110) NdGaO3 and cubic (001) (LaAlO3)0.3-(Sr2AlTaO6)0.7 (LSAT) substrates using pulsed laser deposition with in-situ high pressure reflection high energy electron diffraction. Despite equivalent lattice mismatch and stoichiometry, CaRuO3 on NdGaO3 grows as a coherent single crystal with an atomically smooth surface whereas CaRuO3 on LSAT grows as a multi-domain film with a rough surface. This work suggests that the orthorhombic distortion of the substrate plays an important role in heteroepitaxy. In addition, anisotropic metallic resistivity of the single crystal CaRuO3 was observed to 10 K, with different electrical behavior as a function of temperature for [-110] and [001] in-plane directions. Thus these single domain CaRuO3 thin films offer an opportunity to study the unique physics of this metallic oxide and the growth of strained multiferroic heterostructures such as EuTiO3 to probe magnetoelectric coupling.
9:00 PM - C3.5
Preparation and Selected Properties of Bulk and Thin Film Ferroelectric Calcium Barium Niobate.
Manfred Muhlberg 1 , Manfred Burianek 1 , Barbara Joschko 1 , Paul Ndione 2 , Roberto Morandotti 2 , Mohamed Chaker 2
1 Institute of Crystallography, University of Cologne, Cologne Germany, 2 , INRS-EMT, Varennes, Quebec, Canada
Show AbstractIn contrast to the ferroelectric strontium barium niobate (SBN), calcium barium niobate CaxBa1-xNb2O6 (CBN) exists with a reduced stability region between about 20 and 40 mole percent of Ca. It shows also a ferroelectric phase transition of the type 4/mmm to 4mm. New potential application for the realization of fast integrated electro-optical (EO) modulators are stimulated by the about 200 °C higher Curie temperature of CBN.Transparent [001]-oriented CaxBa1-xNb2O6 (CBN) single crystals with diameters up to 18 mm were grown by the Czochralski method. Several fundamental materials data like refractive indices or Curie temperatures can be only precisely and composition depending determined on the basis of bulk samples with a high crystalline quality. The thermophysical properties of CBN were investigated by DTA and X-ray powder diffraction of annealed samples: there is a congruent melting point at 1472°C and xCa=0.281, and the stability region is reduced to 0.17 < xCa < 0.33 at 1200°C.The accuracy of the refractive index measurements is 10^-5 using goniometer spectroscopy with crystal prisms of high crystalline quality. CBN is uniaxial negative. In contrast to the extraordinary refractive indices (e. g. ne=2.26599) the ordinary refractive indices (e. g. no=2.33513, both values at λ=587.65 μm; xCa=0.288) show nearly no composition dependence. The Curie temperatures determined by calorimetric measurements vary drastically between 293°C (xCa=0.257) and 216°C (xCa=0.311). In parallel, CBN thin films were grown on MgO substrates by pulsed laser deposition technique, using a KrF excimer laser focused on a rotating CBN (xCa=0.28) commercial ceramic target into a vacuum chamber. The depositions were carried out at a working oxygen pressure of 1 mTorr and at a two different temperatures; 700°C and 800°C. Subsequently, the films were cooled in situ under an oxygen atmosphere of 400 mTorr. θ - 2θ X-ray diffraction analysis revealed both polycrystalline and epitaxial (oriented (00l)) nature of the films obtained respectively for deposition temperatures of 700°C and 800°C. The density of the films was measured by X-ray reflectivity technique and was found to be 4.67 and 5.23 g/cm3 for the polycrystalline and for the epitaxial films, respectively. Refractive indices (ordinary) values deduced from spectroscopic ellipsometry technique (with an accuracy of 10-4) and found to be 2.254 and 2.3145 for polycrystalline and for the epitaxial films, at a wavelength of 587 nm. The transmittance measured by infrared spectroscopy technique is 0.75 and 0.87, for polycrystalline and for the epitaxial films respectively. The transition temperature for epitaxial films is determined by Raman spectroscopy technique. The temperature dependence of the Raman spectra of CBN between 300 and 673 K will be discussed. A detailed analysis of the temperature dependence for the wavenumber of the Raman bands suggests that a phase transition takes place at 257°C.
9:00 PM - C3.6
Evolution of Multiferroic Properties in BiFe1-xCrxO3 Epitaxial Films with Chemical and Structural Perturbation.
Dae Ho Kim 1 3 , Michael Biegalski 2 , No Nyung Lee 1 , Hans Christen 1
1 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 3 Department of Physics, Tulane University, New Orleans, Louisiana, United States, 2 Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractThe intriguing coexistence of strong ferroelectric polarization and robust magnetic order make bismuth-based perovskites one of the most extensively studied materials. Here we investigate the properties of ferroelectricity and magnetism under structural and compositional modifications in thin films of BiFe1-xCrxO3. The choice of this materials system is motivated by the large polarization and high transition temperature (P ≥ 100 °C/cm2 and TC = 1103 K, respectively) in BiFeO3 and the recently reported antiferroelectricity in structurally similar BiCrO3.1 By alternating ablation from BiFeO3 and BiCrO3 targets, we have successfully grown a series of BiFe1-xCrxO3 solid-solution epitaxial films on SrTiO3 substrates with various orientations. The films exhibit ferroelectricity up to x = 0.87, transitioning to an antiferroelectric phase at larger x. In films grown on 111 oriented substrates, the polarization directs along the body-diagonal of pseudocubic unit-cell for 0 ≤ x ≤ 0.7. Together with the observed weak strain dependency of polarization in BiFeO3 films on SrTiO3 (001) substrates,2 these results reveal a high stability of the ferroelectric distortion in epitaxial BiFeO3 films. Combined results of magnetization measurements and neutron scattering experiments confirm weak ferromagnetism parasitic to antiferromagnetic order in BiCrO3. Research sponsored by the Division of Materials Sciences and Engineering (DHK, HNL, HMC) and the Division of Scientific User Facilities (MDB), Office of Basic Energy Sciences, U.S. Department of Energy.[1] D. H. Kim et al., Appl. Phys. Lett. 89, 162904 (2006). [2] D. H. Kim et al., Appl. Phys. Lett. 92, 012911 (2008).
9:00 PM - C3.7
Growth of BiFexAl(1-x)O3 by MBE.
Kathryn O'Brien 1 , Jon Ihlefeld 1 , Charles Brooks 1 , Darrell Schlom 1
1 Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania, United States
Show AbstractBiFexAl(1-x)O3 thin films were deposited on (110) substrates of the orthorhombic perovskite, NdGaO3 by molecular-beam epitaxy. A comparison of the four-circle x-ray diffraction spectra of BiFexAl(1-x)O3 and BiFeO3 thin films on (110) NdGaO3 substrates revealed a shift in the positions of the film peaks in 2θ, affirming the solid solution was successfully produced. Optimized growth conditions were at a substrate temperature of 600 C and a purified ozone background pressure of 1x10^-6 torr, with equal compositions of Fe and Al. Lower substrate temperatures did not produce a phase pure sample, but did include some traces of BiFexAl(1-x)O3. The pseudocubic lattice parameter of BiFexAl(1-x)O3 was calculated to be 4.15 Å FOR x=0.5.
9:00 PM - C3.8
Fabrication of Lead-Free Piezoelectric Ceramics (Na0.52K0.44Li0.04)(Nb0.84Ta0.10Sb0.06)O3 [LF4]by a Modified Solid-State Reaction Method.
Masaki Fukada 1 , Takahiro Wada 1
1 Materials Chemistry, Ryukoku University, Otsu Japan
Show AbstractPb(Zr,Ti)O3 (PZT) has been extensively used due to its high piezoelectricity. However, PZT has a drawback from the viewpoint of environmental pollution. In 2004, Saito et al. reported that (Na0.52K0.44Li0.04)(Nb0.84Ta0.10Sb0.06)O3 (LF4) ceramics have excellent piezoelectricity [1]. However, many research groups have tried to fabricate LF4 ceramics with improved piezoelectricity, but most failed to achieve a high piezoelectric constant of d33 >300 pC/N. Recently, we synthesized (Na0.5K0.5)NbO3 (NKN) [2] fine powder through a modified solid-state reaction method in which urea [CO(NH2)2] played an important role. Then we fabricated high-density NKN ceramics using conventional sintering of the obtained fine powder. In this study, we prepared LF4 fine powder by the modified solid-state reaction method. Then we fabricated high-density LF4 ceramics using conventional sintering. The starting materials of sodium oxalate Na2C2O4, potassium oxalate K2C2O4, lithium oxalate Li2C2O4, Nb2O5, Ta2O5, and Sb2O5 were mixed at the following molar ratio: [Na]: [K]: [Li]: [Nb]: [Ta]: [Sb] = 26: 22: 2: 42: 5: 3; the addition of some urea followed. A quantity ratio of [LF4]: [urea] = 1: 1 was adopted in the present study. The mixture was calcined at 500oC for 4 h and re-calcined under similar conditions. The obtained powder was pressed into a disk. One sample was fabricated by sintering at 1130oC for 2 h in air (LF4-Air). The other sample was fabricated by sintering at 1160oC for 2 h in an O2 gas atmosphere (LF4-O2).The phases in the samples were identified by powder X-ray diffraction (XRD). The microstructure of the fractured surfaces was observed using scanning electron microscopy (SEM). Relative dielectric constants εr and loss tangents tanδ were measured using an inductance capacitance- resistance (LCR) meter. The temperature dependences of εr and tanδ were measured in a temperature range from 50 to 350oC. The P-E hysteresis loops were observed at room temperature using a ferroelectric tester. Electromechanical coupling factor kp was measured by the resonance-antiresonance method using an impedance analyzer. Piezoelectric constants d33 were measured by a Berlincourt-type quasistatic d33 meter.The LF4-Air and LF4-O2 ceramics had relative densities of more than 95%. LF4-Air had an εr of 1353 and a tanδ of 0.04, and LF4-O2 had an εr of 1553 and a tanδ of 0.06 at 1 kHz. Curie temperature Tc of the LF4-O2 ceramics was 278oC, which was slightly lower than the Tc of LF4-Air, 287oC. LF4-Air and LF4-O2 ceramics showed saturated P-E hysteresis loops. The Pr and Ec of the LF4-Air ceramic were 20.3 μC/cm2 and 15.0 kV/cm, and LF4-Air showed a d33 of 271 pC/N and a kp of 42%. On the other hand, the Pr and Ec of the LF4-O2 ceramics were 23.0 μC/cm2 and 13.9 kV/cm, and the LF4-O2 ceramics also had a d33 of 314 pC/N and a kp of 45%.[1] Y. Saito et al. Nature 432, 84 (2004).[2] M. Fukada and T. Wada, IEEE TUFFC 55, 988 (2008).
Symposium Organizers
Charles Ahn Yale University
Philippe Ghosez Universite de Liege
Masashi Kawasaki Tohoku University
Darrell Schlom Cornell University
Jean-Marc Triscone University of Geneva
C4/L1: Joint Session: Magnetoelectric Coupling in Multiferroics
Session Chairs
Arunava Gupta
Darrell Schlom
Tuesday AM, December 02, 2008
Room 210 (Hynes)
9:30 AM - **C4.1/L1.4
New Routes to Electric-field Control of Magnetism.
Nicola Spaldin 1
1 Materials Department, University of California, Santa Barbara, California, United States
Show AbstractIn materials which exhibit magnetoelectricity, a magnetic field can be used to modify the electric polarization and an electric field to tune the magnetism. In addition to fundamental interest in controlling order parameters by fields other than their conjugate fields, the electric-field control of magnetism is technologically appealing because of its low power demands and potential for miniaturization. Here we review the fundamentals of the magnetoelectric effect and describe its origin in established magnetoelectric materials. We outline the difficulties associated with calculating magnetoelectric response, then propose some new routes to enhanced magnetoelectricity that have been identified using modern density functional methods.
10:00 AM - **C4.2/L1.2
Dynamical Magnetoelectric Effects in Oxide Multiferroics.
Yoshinori Tokura 1 2
1 Department of Applied Physics, University of Tokyo, Tokyo Japan, 2 ERATO Multiferroics, JST, Tokyo Japan
Show Abstract10:30 AM - C4.3/L1.3
Ferroelectric Control of Carrier Mediated Ferromagnetism in (Fe,Zn)3O4 with High Curie Temperature in Field Effect Transistor Structure.
Hidekazu Tanaka 1 , Junichi Takaobushi 1 , Teruo Kanki 1 , Tomoji Kawai 1
1 ISIR-Sanken, Osaka University, Osaka Japan
Show AbstractFe-based oxides with spinel structure exhibit ferri/ferromagnetism with very high Curie temperature (TC) exceeding 800K. The solid solution system of Fe3-xZnxO4 is one of the best materials for oxide semiconductor spintronics application with high spin polarization above room temperature from the point of view on the large anomalous Hall effect at room temperature, wide tunability on TC, carrier concentration and Density of State at Fermi level [1], [2], [3] with sustainability. There characteristics will lead to advanced spintronics application such as electric field control of ferromagnetism in field effect transistor (FET) structure above room temperature. We report that ferroelectric field control of ferromagnetism at room temperature was achieved in the field effect heterostructure combining the Fe2.5Zn0.5O4 (FZO) with ferroelectric PbZr0.2Ti0.8O3 (PZT). PZT thin film as gate insulator was fabricated using a pulsed-laser deposition (PLD) technique. Nb doped SrTiO3 (Nb-STO) (1wt%) (100) single crystal was used as a substrate and bottom electrode. FZO thin film as channel layer was fabricated on PZT / Nb-STO using a PLD technique. Oxygen atmosphere, PO2, was set to 1.0×10-3 Pa, and substrate temperature TS was 320°C during the deposition. Film thickness of FZO was fixed to 10 and 20 nm. The FZO channel resistance systematically was modulated by ferroelectric polarization through carrier modulation. The Magneto Optic Kerr Effect (MOKE: λ=670nm) confirmed the modulation of ferromagnetism at channel layer in FZO/ PZT FET structure (10nm thickness sample) after applying positive gate bias voltage of +15V (positive ferroelectric remnant polarization (Pr state)) and after applying negative gate bias voltage of -15V (negative Pr state) for ferroelectric gate layer, indicating large ferroelectric remnant polarization (40μC/cm2) modulates ferromagnetism of FZO. The magnetic coercive field (HC) are about 80 Oe in positive Pr state and about 50 Oe in negative Pr state. These results indicate that the predicted ferromagnetic double exchange interaction in spinel ferrite [4, 5] was modulated by ferroelectric electric field effect.References :[1] J. Takaobushi, H. Tanaka, T. Kawai et al, Appl. Phys. Lett., 89 (2006) 242507. [2] J. Takaobushi, S. Ueda, H. Tanaka, T. Kawai et al, Phys. Rev. B, 76 (2007) 205108 , [3] S. Ueda,J. Takaobushi, H. Tanaka, T. Kawai et al, Appl. Phys. Express,(2008) in press, [4] A. Rosencwaig, Phys. Rev. 181 (1969) 946, [5] J. Loos and P. Novák, Phys. Rev. B 66 (2002) 132403
10:45 AM - C4.4/L1.4
Charge-mediated Magnetoelectric Coupling in Complex Oxides with Competing Ground States.
Jason Hoffman 1 2 , Carlos Vaz 1 2 , Hajo Molegraaf 3 , Xia Hong 4 , 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 Phenomenon, Yale University, New Haven, Connecticut, United States, 3 DPMC, Université de Genève, Genève Switzerland, 4 Physics, Penn State University, State College, Pennsylvania, United States
Show Abstract Current efforts to exploit materials with multifunctional capabilities have rekindled interest in multiferroics, which display a coupling between magnetic and electric order parameters. Combining dissimilar magnetic and ferroelectric systems is one approach to optimize this coupling. In particular, large magnetoelectric coupling may be expected in strongly correlated magnetic materials exhibiting competing ground states. Here, we demonstrate charge-mediated magnetoelectric coupling in ferroelectric / lanthanum manganite heterostructures, including the electric field-controlled on/off switching of magnetism. In this work, off-axis RF magnetron sputtering was used to grow epitaxial ferroelectric Pb(Zr,Ti)O3 (PZT) / La0.8Sr0.2MnO3 (LSMO) heterostructures with high crystalline quality, atomically smooth surfaces, and low leakage current density. X-ray diffraction reveals c-axis oriented growth of PZT, with a root-mean-square (RMS) surface roughness of ~5Å. We employ magneto-optic Kerr effect (MOKE) magnetometry to directly probe the magnetic response as a function of the applied electric field, showing a large carrier-mediated magnetoelectric coupling, which can be understood within the double-exchange model. This experiment demonstrates a charge-based mechanism for the coupling between magnetic and electric order parameters in ferroelectric / Sr-doped lanthanum manganite heterostructures, which may permit the development of room temperature magnetoelectric devices with large coupling between electric and magnetic degrees of freedom.
11:30 AM - C4.5/L1.5
Hybrid Multiferroic System: Non-Volatile Control of Ferromagnetism in (Ga,Mn)As Gated by Ferroelectric Polymer.
Igor Stolichnov 1 , Sebastian Riester 1 , Nava Setter 1 , Joe Trodahl 1 2 , Andrew Rushforth 3 , Kevin Edmonds 3 , Richard Campion 3 , Thomas 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, Praha Czechia
Show AbstractA new multicomponent multiferroic system where the ferromagnetism in the (Ga,Mn)As diluted magnetic semiconductor is modulated by polarization reversal in the ferroelectric gate has been successfully implemented. To overcome the apparent processing incompatibility between the magnetic semiconductor and gate ferroelectric we apply a ferroelectric co-polymer polyvinylidene fluoride with trifluoroethylene P(VDF-TrFE) characterized by relatively benign processing demands, in particular a low thermal budget. Use of (Ga,Mn)As in a multiferroic system is of particular interest, since this thoroughly investigated material is considered among the chief candidates for spintronic applications. The origin of the electric-field control of the ferromagnetism in this material is well understood in terms of the Mn-Mn exchange interaction by the strongly spin-orbit coupled valence band holes. The ferromagnetic Curie temperature Tc in (Ga,Mn)As is a significant function of the hole density, which offers the potential for altering the ferromagnetic response by the electric-field[1]. The ferroelectric gate control of ferromagnetism demonstrated in this work adds to this multiferroic FET device concept a qualitatively new feature of non-volatile operation. In the first proof-of-concept study performed on the 7 nm (Ga,Mn)As layer gated with the 200 nm P(VDF-TrFE) film we demonstrated that the polarization reversal by 30V pulses results in a persistent modulation of the ferromagnetic properties in the channel[2]. Magnetotransport and extraordinary Hall effect measurements allowed for inferring a Tc shift associated with ferroelectric polarization switching of 3.8K (4.7%), which is in a good agreement with the established understanding of hole-mediated exchange in (Ga,Mn)As. The magnitude of the gate effect and strength of the ferromagnetism modulation was considerably lower than the estimation based on the switching polarization charge. Study of the polarization stability using piezo-force microscopy in combination with the switching dynamics suggest that the gate effect is limited by a partial screening of the ferroelectric polarization. In this work we explore the possibilities to maximize the gate effect via the processing optimization of the ferroelectric polymer gate and appropriate selection of the polymer composition. The presented concept of the hybrid multiferroic FET suggests that the functionalities of ferroelectric field effect devices extend much further beyond the conventional non-volatile memories and may be of interest for spintronic logic elements.1. Dietl, T. & Ohno, H. Materials Today 9, 18(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. Nature Materials 7, 464 (2008).
11:45 AM - C4.6/L1.6
Novel FeGaB Thin Films and Giant Microwave Tunability in FeGaB/PMN-PT Multiferroic Composites.
Jing Lou 1 2 , David Reed 1 2 , Carl Pettiford 1 2 , Ming Liu 1 2 , Nian Sun 1 2
1 Electrical and Computer Engineering, Northeastern University, Boston, Massachusetts, United States, 2 Center for Microwave Magnetic Materials and Integrated Circuits, Northeastern University, Boston, Massachusetts, United States
Show Abstract Multiferroic composite materials with strong magnetoelectric (ME) coupling have led to many novel devices such as pico-Tesla sensitivity magnetoelectric magnetometers, electro-statically tunable microwave magnetic signal processing devices, etc. In order to achieve strong ME coupling with large frequency tunability at microwave frequencies, the magnetic phase in microwave multiferroic composites needs to have low ferromagnetic resonance (FMR) linewidth, large saturation magnetostriction constant (λs), high permeability and low saturation magnetic field. Single crystal yttrium iron garnet (YIG) has been the magnetic material of choice for tunable multiferroic microwave devices due to its narrow FMR linewidth. However, its low λs (~1.4 ppm) and low magnetization has severely limited the frequency tunability to be Δf ≤ 120 MHz and Δf/f ≤ 2.5%. In this work, we report on a new class of FeGaB magnetic films with high λs and their applications in multiferroic materials. With the increase of boron content, the λs of the FeGaB alloys showed a nonlinear behavior. A maximum λs of 72 ppm was achieved at 12 at. % of boron. Meanwhile, the FMR linewidth measured at X-band got dramatic reduced from ~700 Oe for binary FeGa film to < 20 Oe with boron content larger than 9 at. %, which is desired for ME tunable microwave devices. Multiferroic composites of FeGaB/lead magnesium niobate-lead titanate (PMN-PT) were made and their ME coupling was studied. The FeGaB/PMN-PT multiferroic composite show giant ME coupling at microwave and DC frequencies. A record-high microwave frequency tunability of Δf = 900 MHz or Δf/f = 58% was achieved in the composite with the change of external electric field from -6 kV/cm to +2 kV/cm. A strong electric field dependence of magnetic hysteresis loops was observed as well, which led to switched magnetic easy and hard axes. These FeGaB films have potential applications in RF/microwave multiferroic composite materials and devices.References:[1] J. Lou, R. E. Insignares, Z. Cai, K. S. Ziemer, M. Liu, and N. X. Sun, "Soft magnetism, magnetostriction, and microwave properties of FeGaB thin films", Appl. Phys. Lett. 91, 18254 (2007).[2] J. Lou. D. Reed, C. Pettiford, M. Liu, P. Han, S. Dong, and N. X. Sun, "Giant microwave tunability in FeGaB/lead magnesium niobate-lead titanate multiferroic composites", Appl. Phys. Lett. in press.
12:00 PM - C4.7/L1.7
Magnetoelectric Effect in Ferroelectric-antiperovskite Heterostructure.
Pavel Lukashev 1 , Renat Sabirianov 1
1 Physics, University of Nebraska, Omaha, Omaha, Nebraska, United States
Show AbstractWe report theoretical prediction of linear magnetoelectric effect (ME) in ferroelectric-antiperovskite PbTiO3/Mn3GaN heterostructure. The origin of the ME effect arises from the sensitivity of the Mn3GaN's magnetization to structural deformations which lowers its symmetry, i.e. piezomagnetic effect. Besides the recently proposed strain mediated coupling between magnetic and electric components of heterostructure, we observe a propagation of the soft mode atomic displacements from ferroelectric to the antiperovskite phase. Such deformations further lower the symmetry and increase the induced magnetization. The observed effect is linear, i.e. magnetization induced due to the soft mode propagation is reversed upon reversal of polarization. The first-principles calculations based on 25 atoms unit cell show that net magnetization of about 2 µB per 25 atom cell is induced. The magnetic symmetry is very sensitive to the nature of the interface. Free surface of Mn3GaN shows noticeable relaxation of surface layers and the rotations of local magnetic moments associated with these surface deformations. We find that this does not lead to the larger values of the induced net magnetization in the slab geometry. The calculations were performed by projector augmented wave method.
12:15 PM - **C4.8/L1.8
Unanticipated Consequences of Spin-Orbit Coupling in Half Metallic Ferromagnets.
Warren Pickett 1 , Kwan-woo Lee 1
1 Department of Physics, University of California-Davis, Davis, California, United States
Show AbstractTypically spin-orbit coupling (SOC) has been expected to degrade half metallic ferromagnetism slightly by mixing the spins, but usually with negligible consequences. In compounds containing 5d transition metal elements, however, the large spin-orbit coupling leads to unanticipated consequences, which are illustrated by two double perovskite compounds. In Ba2NaOsO6, the unconnected OsO6 octahedra based on heptavalent Os have a momentless ground state due to strong SOC. Hybridization between these clusters tends toward quenching of the orbital moment, leading to the emergence of magnetism from the nonmagnetic reference state. The double perovskite Sr2CrOsO6, based on pentavalent 5d Os and trivalent 3d Cr, is calculated to be a compensated ferrimagnetic ("half metallic antiferromagnet") if SOC is neglected. The large SOC leads to spin and orbital moments and net ferrimagnetic order. Surprisingly, in the isovalent compound Sr2CrRuO6, the (smaller) SOC also leads to changes in the spin and orbital moments, but these changes cancel leaving the compensated ferrimagnetic character. These density functional based results will be put in the context of the experimental information that is available.
12:45 PM - C4.9/L1.9
Magnetoelectric Coupling Through Exchange Bias at La0.7Sr0.3MnO3/BiFeO3 Interfaces.
Mark Huijben 1 2 , Ying-Hao Chu 2 3 , Lane W. Martin 2 4 , Martin Couillard 5 , Hajo Molegraaf 1 6 , Jan Seidel 2 4 , Nina Balke 2 , Pu Yu 2 , Micky B. Holcomb 2 , Guus Rijnders 1 , Jean-Marc Triscone 6 , David A. Muller 5 , Silvia Picozzi 7 , Elbio Dagotto 8 9 , Dave Blank 1 , R. Ramesh 2 4
1 Faculty of Science and Technology and MESA+ Institute for Nanotechnology, University of Twente, Enschede Netherlands, 2 Department of Physics & Department of Materials Science and Engineering, University of California, Berkeley, Berkeley, California, United States, 3 Department of Materials Science and Engineering, National Chiao Tung Unviersity, HsinChu Taiwan, 4 Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 5 School of Applied and Engineering Physics, Cornell University, Ithaca, New York, United States, 6 DPMC, University of Geneva, Geneva Switzerland, 7 , CNR INFM, L’Aquila Italy, 8 Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee, United States, 9 Division of Materials Science & Technology, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractMultiferroics exhibiting simultaneously multiple order parameters, such as magnetism and ferroelectricity, offer an exciting way to explore coupled phenomena in solids. These investigations are driven by the prospect of magnetoelectric coupling in which charges are controlled by applied magnetic fields and spins by applied voltages. The recent availability of high-quality thin-film samples of hexagonal manganites and Bi-based perovskites, has improved the ability to accurately characterize multiferroic behavior, and has opened the door to the fabrication of practical devices based on magnetoelectric coupling. Currently, bismuth ferrite BiFeO3 (BFO) is being intensely explored since both ferroelectric (~820 oC) and antiferromagnetic (~370 oC) ordering temperatures are much higher than room temperature, which make it appealing for ambient applications. Recent studies have demonstrated the existence of strong coupling between ferroelectricity and antiferromagnetism. Thus, rotation of the ferroelectric order by 71 and/or 109 degrees leads to a corresponding rotation of the antiferromagnetic order. In order to manifest this intrinsic coupling into applications, it would be highly desirable to be able to control ferromagnetism. Since the intrinsic canted ferromagnetism in BFO is too small in magnitude to be useful, current approaches have focused on heterostructures consisting of a ferromagnet in intimate contact with the multiferroic. These studies have used a conventional metallic ferromagnet such as Co0.9Fe0.1 to couple to the BFO through exchange coupling at the interface. Due to the significant differences in chemistry between Co0.9Fe0.1 and BFO, the conventional exchange bias thermal annealing process cannot be used; instead, the ferromagnet is grown on the BFO in an applied field, typically ~200 Oe. The existence of double exchange coupled ferromagnets such as La0.7Sr0.3MnO3 (LSMO) provides us with an alternative approach to probe magnetic coupling at interfaces. Within this framework, we report the first observation of exchange bias coupling between the ferroelectric/antiferromagnet (multiferroic) BFO and the ferromagnet (LSMO) in high quality heterostructures. We will provide a suggestion for the cause of this interesting interface effect based on results from an extensive amount of magnetic measurements, structural analysis measurements (such as STEM-EELS) and first principles calculations. Finally, we will show the first indications of magnetoelectric coupling at these interfaces by magneto-optical Kerr effect measurements, while switching the polarization direction.
C5: BiFeO3 - Ferroelectric and Magnetic Properties
Session Chairs
Tuesday PM, December 02, 2008
Room 210 (Hynes)
2:30 PM - **C5.1
Domain and Strain Engineering of Epitaxial BiFeO3 Thin Films for Enhanced Ferroelectric Properties.
Chang-Beom Eom 1
1 Materialas Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States
Show AbstractWe have demonstrated significant enhancement of ferroelectric properties of epitaxial (001) BiFeO3 thin films by domain and strain engineering. BiFeO3 on miscut (001) SrTiO3 substrates have two-variant stripe domains and show high remanent polarization and low leakage current density. We also demonstrated a strong tunability of remanent polarization of (001) epitaxial BiFeO3 thin films and free standing membranes. Thermodynamic analysis reveals that a strain-induced polarization rotation mechanism is responsible for the large change in the out-of-plane polarization with biaxial strain while the spontaneous polarization itself remains almost constant. Fatigue-free switching behavior up to 10^10 cycles was observed for BiFeO3 membranes with Pt top electrodes.This work has been done in collaboration with H. W. Jang, S. H. Beak, D. Ortiz, C. M. Folkman, Y. H. Chu, J. X. Zhang, V. Vaithyanathan, Y. B. Chen, X. Q. Pan, D. G. Schlom, L. Q. Chen, and R. Ramesh. The authors gratefully acknowledge the financial support of the National Science Foundation through grants ECCS-0708759, DMR-0507146, and the Office of Naval Research through grant N00014-05-1-0559.
3:00 PM - **C5.2
Electrical Field Control Of Ferromagnets Using Multiferroics.
Ramamoorthy Ramesh 1
1 Department of Materials Science and Engineering and Department of Physics, University of California, Berkeley, Berkeley, California, United States
Show Abstract3:30 PM - C5.3
Temperature Dependent A.C. Conductivity and Dielectric Properties of Chemical Solution Deposited BiFeO3 Thin Films.
Amar Srivastava 1 , Ashish Garg 1
1 Materials and Metallurgical Engineering, Indian Institute of Technology Kanpur, Kanpur, U.P., India
Show Abstract3:45 PM - C5.4
Ferroic Phase Transitions in BiFe1-xMnxO3, 0 ≤ x ≤ 0.3.
Sverre Selbach 1 , Thomas Tybell 2 3 , Mari-Ann Einarsrud 1 , Tor Grande 1
1 Department of Materials Science and Engineering, Norwegian University of Science and Technology, Trondheim Norway, 2 Department of Electronics and Telecommunications, Norwegian University of Science and Technology, Trondheim Norway, 3 NTNU NanoLab, Norwegian University of Science and Technology, Trondheim Norway
Show AbstractThe ferroic phase transitions [1] of multiferroic BiFeO3 have been characterized and a phase diagram [2] for BiFe1-xMnxO3 is presented. The antiferromagnetic to paramagnetic phase transition at the Néel temperature TN of 643 K is second order and associated with anomalous, continuous volume expansion. An anomaly in activation energy for electronic conduction is also observed at the loss of antiferromagnetic order. Both TN and ferroelectric TC (1103 K for x = 0) decreases linearly with increasing Mn content. The ferroelectric to paraelectric phase transition is first order with large, discontinuous volume contraction and discontinuous electronic conductivity. The paraelectric crystal structure belongs to the space group R-3c, and is thus expected to be ferroelastic. The crystallographic order parameter of the phase transition is the cooperative displacement of Bi3+ and Fe3+ along the polar [111] pseudocubic axis. BiFe1-xMnxO3 retains the R3c space group for x up to 0.3. In BiFe0.7Mn0.3O3 the phase transition to the aristotype crystal structure of an ideal cubic perovskite (space group Pm-3m) takes place at 1036 ± 10 K. The R-3c to Pm-3m ferroelastic phase transition is continuous second order, and the crystallographic order parameter is the antiferrodistortive rotation of Fe(Mn)O6 octahedra about the [111] pseudocubic axis. BiFe0.7Mn0.3O3 thus exhibits the phase transition sequence: R3c (antiferromagn.) ↔ R3c (paramagn.) ↔ R-3c (paraelectric, ferroelastic) ↔ Pm-3m. Finally, finite size effects of BiFeO3 nanocrystals are discussed.[3]
[1] S. M. Selbach, T. Tybell, M.-A. Einarsrud, T. Grande, Adv. Mater. In press.
[2] S. M. Selbach, T. Tybell, M.-A. Einarsrud, T. Grande, To be submitted to Phys. Rev. Lett.
[3] S. M. Selbach, T. Tybell, M.-A. Einarsrud, T. Grande, Chem. Mater. 19 (2007) 6478-6484.
4:30 PM - C5.5
Oxygen Vacancy Levels in Multiferroic BiFeO3.
John Robertson 1 , Stewart Clark 2
1 Engineering Dept, Cambridge University, Cambridge United Kingdom, 2 , Durham University, Durham United Kingdom
Show Abstract4:45 PM - C5.6
Enhancement of Ferroelectric Properties of Epitaxial BiFeO3 Thin Films on La-doped SrTiO3 Single Crystal.
Seiji Nakashima 1 , Jung Min Park 1 , Takeshi Kanashima 1 , Hironori Fujisawa 2 , Masaru Shimizu 2 , Masanori Okuyama 1
1 Graduate school of engineering science, Osaka University, Toyonaka, Osaka, Japan, 2 Graduate school of engineering, University of Hyogo, Himeji, Hyogo, Japan
Show Abstract Multiferroics have attracted much attention from viewpoint of application such as memory, 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 K, and has tetragonal structure, which is also different from bulk BFO structure.1) Here, if the crystalline orientation is aligned to the polarization direction ((001) in tetragonal structure or (111) in rhombohedral structure), larger Pr is also expected to be obtained in epitaxial BFO thin films.In this study, 350-nm-thick epitaxial BFO thin films have been directly grown on (001), (110), and (111) La-doped SrTiO3 (La-STO) conducting single crystal substrates by PLD using an ArF excimer laser (λ = 193 nm). Substrate temperature and O2 pressure were at 500oC and 0.12 Torr, respectively. After deposition of top Pt electrode with a diameter of 186 μm by sputtering, electric properties have been investigated at various temperatures below RT, and crystal structures have been also investigated at RT. Reciprocal space mappings at RT indicate the BFO thin films on La-STO (001) and (111) have tetragonal and rhombohedral structures, respectively. However, we couldn’t distinguish whether crystal structure of the BFO thin film on La-STO (110) is monoclinic or rhombohedral structure. From D-E hysteresis measurements at 80 K, epitaxial BFO thin films on La-STO (001), (110) and (111) show large remanent polarizations of 61, 110 and 147 μC/cm2 at a maximum applied electric field of 1312 kV/cm (45 V) , 1020 kV/cm (35 V) and 857 kV/cm (30 V), respectively. The D-E hysteresis loops show good saturation properties and have almost the same D-E characteristics at various scanning frequencies of 50 ~ 1 kHz. Moreover, J-E characteristics of the BFO thin films on La-STO (001), (110) and (111) at 80 K show low leakage current of 1.0×10-4, 1.8×10-4, and 8.7×10-5 A/cm2 at a applied electric field of 857 kV/cm (30 V), respectively. Remanent polarizations were measured by pulsed polarization method using positive-up-negative-down (PUND) pulses, and agree well with those of conventional D-E hystereses. Therefore, it is considered that such large remanent polarizations are due to ferroelectricity but not the other origins like leakage current and ion drift. Reference1) K. Y. Yun, D. Ricinschi, T. Kanashima, M. Noda, and M. Okuyama, Appl. Phys. Lett. 89, 192902 (2006).
5:00 PM - C5.7
Ultrafast Functionality and Photo-Assisted Switching of the Ferroelectric Polarization in BiFeO3 Thin Films.
Dhanvir Rana 1 , Iwao Kawayama 1 , Krushna Mavani 1 , K. Takahashi 1 , H. Murakami 1 , M. Tonouchi 1
1 Institute of Laser Engineering, Osaka University, Osaka, Osaka-fu, Japan
Show AbstractPerovskite BiFeO3 has attracted considerable attention recently because of its multiferroic behavior at room temperature, large spontaneous polarization, and scope for epitaxial strain engineering of magnetoelectric properties in thin films. Its antiferromagnetic behavior and large coercivity of ferroelectric behavior, that inhibit direct use of its magnetoelectric properties for multiple state memory devices, has spurred researchers to explore alternate approaches to enhance possibilities of its technological utility [1]. In the present work, we have investigated the photo functionality and the ultrafast dynamics of spontaneous polarization in ferroelectric memory of BiFeO3 by employing terahertz (THz) emission spectroscopy [2]. The ferroelectric polarization of BiFeO3 in the (111) crystallographic plane implies that THz emission spectroscopy along all three (100), (110) and (111) orientations should show distinct features. We have observed THz-emission from all the BiFeO3 (100), (110) and (111) thin films. The emission from BiFeO3 (100) and (110) films exhibits the hysteretic dependence on the applied electric-field, which directly reflects its hysteretic ferroelectric properties [Fig. 1]. The coercivity of ~70-100 kV/cm of these loops compared to the coercivity of ~300-500 kV/cm of conventional ferroelectric loops depicts a photo-assisted polarization switching phenomenon in the former. This effect becomes even more pronounced when the dipole gap of photoconductive antenna is reduced. Also, photo-assisted poling [3] increases the THz-emission amplitude and this improvement in THz radiation flux is a signature of enhanced data storage densities. We further show that the THz-emission from BiFeO3 (111) films has linear electric-field dependence and has the opposite polarity compared to THz-emission from (100) and (110) films [Fig. 1]. Investigating the different origin of emission from (100) and (110) films vis-à-vis (111) films, we demonstrate the emission from the former pair occurs as a result of ultrafast depolarization of the ferroelectric order over a picosecond time scale, followed by its non-destructive retrieval. This transient depolarization occurs via a non-thermal process which signifies the ultrafast non-destructive data read-out. [1] R. Ramesh and N.A. Spaldin, Nature Mater. 6, 21 (2007).[2] K. Takahashi, N. Kida and M. Tonouchi, Phys. Rev. Lett. 96, 117402 (2006).[3] K. Takahashi and M. Tonouchi, Appl. Phys. Lett. 90, 052908 (2007)
5:15 PM - C5.8
Understanding Magnetism in Multiferroic BiFeO3 Thin Films.
Lane Martin 1 , Mikel Holcomb 2 , Ying-Hao Chu 1 , R. Ramesh 1 2 3
1 Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 2 Physics, University of California, Berkeley, Berkeley, California, United States, 3 Materials Science and Engineering, University of California, Berkeley, Berkeley, California, United States
Show AbstractRecently there has been much attention given to multiferroic materials as one pathway to obtaining new functionalities in devices. The goal of such work would is to control ferromagnetism with an electric field. Although novel layered heterostructures have been shown to manifest such behavior at room temperature, no single-phase multiferroic has yet been found that is simultaneously both ferromagnetic and ferroelectric at room temperature. Thus successful production of such a material would be of great interest. With this in mind, the nature of magnetism in the widely studied multiferroic material BiFeO3 (BFO) has been the focus of many experimental and theoretical studies over the past few years. BFO is a known magnetoelectric material in which the ferroelectric and antiferromagnetic order parameters are coupled. There have been a number of reports, however, of varying magnetic properties in this material including the measurement of large intrinsic moments in strained BFO thin films that far exceed the expected moment (~6-10 emu/cc) resulting from a canting of the antiferromagnetic moments in BFO. The nature of and origin of this moment has been a matter of great contention and the question remains whether researchers can control such a material to have a significant magnetic response. In this work we report the growth and detailed magnetic characterization of a wide array of BFO thin films – including (001), (110), and (111) oriented films on numerous substrates. By combining our ability to carefully control the nature of thin films of BFO – including control of the multiferroic domain structure, strain state of the film, and stoichiometry of the films – we are offered new avenues to explore the nature of and origin of magnetism in this system. We have observed a direct correlation between the magnitude of the magnetic moments observed in BFO and the underlying domain structure and strain state of the films. By controlling BFO to have a “mosaic-like” or complex domain structure we can enhance the magnetization of the films. On the other hand, BFO films with “stripe-like” domains consistently exhibit moments in the theoretically predicted 6-10 emu/cc range. Additionally we will discuss the role of oxygen stoichiometry, A-site doping, and thin film strain in enhancing the magnetism in BFO thin films. Through a combined study of thin film growth and careful magnetic measurement utilizing both laboratory and synchrotron based measurement techniques, we believe it is possible to understand the varied reports of magnetism in BFO based on a careful understanding of these important factors that can be controlled during growth. We aim to understand how the crystal structure, symmetry, and magnetic order parameters are interrelated in this material and how this presents insight into the fundamental nature of magnetism in these complex multiferroic materials. This work is supported by the Department of Energy.
5:30 PM - C5.9
Evolution of In-plane Ferroelectric Domain Structure in Epitaxial BiFeO3 Thin Films.
Nina Balke 1 , Martin Gajek 2 , Lane Martin 2 , Padraic Shafer 1 , Ying-Hao Chu 3 , Ramamoorthy Ramesh 1 2
1 Department of Materials Science and Engineering, University of California Berkeley, Berkeley, California, United States, 2 Department of Physics, University of California Berkeley, Berkeley, California, United States, 3 Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu Taiwan
Show AbstractMultiferroic BiFeO3 (BFO) has been widely studied for its ferroelectric and antiferromagnetic properties. The coupling between these order parameters makes this material very attractive for novel new memory devices based on such magnetoelectric coupling. Before one can understand the coupling of the different order parameters, however, the nature of domain switching must be completely understood. One current focus is in understanding how to control the formation of specific ferroelectric domain walls with varying applied electric fields. Such an ability is of great interest since it has been shown that different domain walls (i.e., 71°, 109°, or 180°) can have different physical properties. In order to investigate the domain switching in BFO thin films in detail, we have turned to model structures based on in-plane electrodes. The various in-plane ferroelectric switching events are achieved and studied by applying voltage pulses to the electrodes and imaging the area between the electrodes using Piezoresponse Force Microscopy (PFM). In this work, we will show in detail how the domains switch between the in-plane electrodes and how the domain structure develops after several switching cycles. Initial evidence shows the evolution of large, singly polarized ferroelectric domains after only a few switching events. We will discuss the energetic of these domain structures and the possible causes for the formation of such domain structures.
5:45 PM - C5.10
Hole Doping BiFeO3.
Chan-Ho Yang 1 , J. Seidel 1 4 , S. Kim 2 , P. Rossen 2 , M. Chi 3 , P. Yu 1 , L. Martin 2 4 , M. Holcomb 1 4 , N. Balke 2 , M. Gajek 1 , Y. Chu 5 , M. Huijben 1 , M. Scullin 2 , S. Crane 2 , P. Shafer 2 , S. Basu 1 , S. Park 6 , T. Koo 6 7 , K. Ko 6 , J. Park 6 , Y. Jeong 6 , N. Browning 3 , R. Ramesh 1 2 4
1 Physics, University of California, Berkeley, California, United States, 4 Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 2 Material Science and Engineering, University of California, Berkeley, California, United States, 3 Material Science and Engineering, University of California, Davis, California, United States, 5 Material Science and Engineering, National Chiao Tung University, HsinChu Taiwan, 6 Physics and electron Spin Science Center, Pohang University of Science and Technology, Pohang Korea (the Republic of), 7 Pohang Accelerator Laboratory, Pohang University of Science and Technology, Pohang Korea (the Republic of)
Show AbstractMimicking colossal magnetoresistance manganites and high-Tc cuprates, a divalent ion doping effect on a multiferroic BiFeO3 is investigated. Long-range oxygen vacancy ordering and control of its modulation period by different doping ratio were firstly discovered in this system and systematically investigated to build up phase diagram. It was experimentally observed that ferroelectric instability exceptionally disorders the superstructure around x ~ 0.125 and makes a base for an exotic electric field driven phase transition from ferroelectric insulating state to a conducting state. The conductivity changes three orders of magnitude and reversibly returns to the original insulating state by opposite electric field. This transition occurs homogeneously with the spatial resolution of 100 nm according to conducting atomic force microscopy (c-AFM). This material can be potentially used for non-volatile resistive random access memory (RRAM).
C6: Poster Session: Characterization of Multiferroic Materials
Session Chairs
Wednesday AM, December 03, 2008
Exhibition Hall D (Hynes)
9:00 PM - C6.1
Effect of V Doping on the Dielectric Properties of ZnO.
E. Senthil Kumar 1 , Ravinchandra Reddy 1 , Mamidanna Rao 1
1 Department of Physics, Materials Science Research Centre and Nano Functional Material Technology Centre, Indian Institute of Technology Madras, Chennai, Tamil Nadu, India
Show Abstract9:00 PM - C6.10
Synthesis and Electrical Properties of Electron-doped Ruddlesden-Popper Homologous Series Thin Films.
Masaki Okude 1 , Akira Ohtomo 1 , Takuji Kita 2 , Masashi Kawasaki 1 3 4
1 Institute for Materials Research, Tohoku University, Sendai Japan, 2 , Toyota Motor Corporation, Toyota Japan, 3 WPI Advanced Institute for Materials Research and Institute for Materials Research, Tohoku University, Sendai Japan, 4 CREST, Japan Science and Technology Agency, Tokyo Japan
Show AbstractAtomic-scale control of complex oxide heteroepitaxy is of growing importance in the viewpoints of both fundamental physics and device applications. Many of intriguing physical phenomena including high-Tc superconductivity, ferromagnetism, ferroelectricity, and multiferroicity occur in naturally layered structures of transition metal oxides, giving rise to challenges for epitaxial synthesis of new compounds upon the atomic-scale layer-by-layer growth of artificial superlattices. Ruddlesden-Popper (RP) homologous series, is Srn+1TinO3n+1, a prototypical layered compound to design the physical properties by changing the stacking sequence. However, pulsed-laser deposition (PLD), one of the most widely used techniques, has been only capable of growing heavily disordered RP phase films. We have recently developed a PLD growth route of well-ordered RP phase films with using repeated temperature modulation technique [1]. Here we present epitaxial synthesis of La3+-doped RP homologous series films (LaxSr1-xO)/(STO)n) on STO substrates. X-ray diffraction measurements revealed clear satellite peaks reflecting the well-ordered layered structure. The films exhibited systematic dependence of resistivity on n value. The n = 5 film showed metallic conductivity down to 20 K (ρ = 1 x 10-2 Ωcm), while the n = 2 film was less conducting (ρ ≥ 10 Ωcm). Carrier concentration at room temperature of n = 5 film was measured to 1.7 x 1020 cm-3, which is approximately one order magnitude lower than doped La concentration.[1] M. Okude et al., a manuscript submitted to Appl. Phys. Express.
9:00 PM - C6.11
Modeling Nonlinearity in Ferroelectrics.
Ichiro Fujii 1 , Eunki Hong 1 , Susan Trolier-McKinstry 1 , Craig Nies 2 , Michael Muir 2
1 Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania, United States, 2 Advanced Products and Technology Center, AVX Corporation, Myrtle Beach, South Carolina, United States
Show AbstractAs BaTiO3-based capacitors utilize progressively thinner layers (now < 1μm) due to demand for high capacitance at small sizes, the small signal dielectric properties cannot properly describe the observed dielectric response. In this study, the ac and dc electric field dependence of the dielectric permittivity of undoped BaTiO3 ceramics, BaTiO3-based sample multilayer capacitors with X7R specifications, and PZT film capacitor was successfully modeled with a Preisach model. The first order reversal curves method was used to determine the Preisach distribution function. A strong concentration of irreversible hysterons was found for the BaTiO3 ceramics and the PZT film, but not for the X7R multilayer capacitor. For the X7R multilayer capacitor, the Preisach model was applied up to fields of 60 kV/cm. It was found that the Preisach model gave reasonable agreement to measured ac field dependence of the dielectric constant as well as effect of the dc bias fields on the ac field dependence. The Preisach model is useful in predicting the dielectric property of the samples over wide field range.
9:00 PM - C6.12
Effects of Oxygen Content on Photoinduced Properties of Bi1-xCaxMnO3 Thin Films.
Vera Smolyaninova 1 , Grace Yong 1 , Rajeswari Kolagani 1 , Khim Karki 1
1 Dept. of Physics, Astronomy and Geosciences, Towson University, Towson, Maryland, United States
Show AbstractDoped rare-earth manganese oxides (manganites) exhibit a large diversity in electronic, magnetic, and orbital states due to the complex interplay of the corresponding degrees of freedom. Application of modest external fields may drastically modify the state of such materials. A photoinduced insulator to conductor transition in thin films of Bi0.4Ca0.6MnO3 associated with melting of the charge ordering [1] is especially interesting from the point of view of creating photonic devices. We report a study of conductive, structural and photoinduced properties of Bi1-xCaxMnO3 thin films with different oxygen content grown on different substrates. The role of growing and annealing conditions will be discussed. The change in magnitude and lifetime of photoinduced changes in films with different oxygen content will be reported. The possible origin of these changes will be discussed. This work is supported by the NSF grants DMR-0348939 and DMR-0453342. [1] V. N. Smolyaninova at al., Phys. Rev. B 76, 104423 (2007)
9:00 PM - C6.13
Epitaxial Multiferroic Relaxor Pb(Fe2/3W1/3)O3 Thin Films.
Ashok Kumar 1 , Ram Katiyar 1
1 Department of Physics, University of Puerto Rico, San Juan, Puerto Rico, United States
Show AbstractEpitaxial multiferroic Pb(Fe2/3W1/3)O3 thin films were fabricated on MgO substrates by pulse laser deposition technique. The surface morphology indicates homogeneous distribution of grain with an average surface roughness ~ 2-5 nm. Frequency dispersion in dielectric spectra and dielectric maximum temperature were observed near 180 K suggests relaxor nature of PFW thin films. Modified Curie-Weiss law and non-linear Vogel-Fulcher fitting further confirms the relaxor behavior. Dielectric characteristic were further studied using different DC bias field (~ 5-50 kV/cm) over wide range of temperature to investigate the polarization properties below freezing temperature. Change in dielectric properties of PFW thin films for different thickness from 100 nm to 600 nm were also investigated. The impedance spectroscopy was carried out to check the grain and grain boundary effects near the dielectric dispersion regions. Magnetization vs. applied magnetic field displayed weak ferromagnetic properties. Temperature dependent polarized Raman spectroscopy were carried out to investigate the change in crystal structure, lower frequency F2g phonon mode, A1g phonon mode near the dielectric dispersion region.
9:00 PM - C6.14
Wurtzite-Perovskite-Wurtzite (ZnO-BaTiO3-ZnO) Interface Polarization Hysteresis Model.
Venkata Voora 1 , T. Hofmann 1 , M. Brandt 2 , M. Lorenz 2 , M. Grundmann 2 , M. Schubert 1
1 Department of Electrical Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska, United States, 2 Institut für Experimentelle Physik II, Universität Leipzig, Leipzig Germany
Show AbstractHeterojunctions composed of symmetrically (ZnO-BaTiO3-ZnO) wurtzite-structure ZnO and perovskite-structure BaTiO3 are interesting because of the coupling between the switchable lattice charge of the perovskite structure (BaTiO3), which is here sandwiched between the wurtzite-structure (ZnO), with non-switchable ionic charge of ZnO. The ZnO and BaTiO3 layer stack was deposited by pulsed laser deposition on (001) silicon substrate using a rotatable multi-target holder. The polarization hysteresis properties were investigated in order to study the polarization (lattice charge) exchange coupling behavior. The heterostructure reveals strong reversible resistive and capacitive switching for positive and negative voltages, and hysteresis due to the ferroelectric polarization. Depletion layer formation in ZnO, which occurs for both positive and negative input voltages, is the origin of the highly resistive behavior for DC currents, and which can be controlled by the ferroelectric polarization in the BTO layer. We develop a physical model approach by implementation of the double sandwich structure into our previous model approach for a single interface ZnO-BTO structure [1]. We analyze the Sawyer-Tower response of our experimental structure with this model. Our model accounts for the depletion charges, the non-switchable lattice charge of ZnO, and the switchable charge lattice charge of BaTiO3. The model data are in excellent agreement with the measured voltage dependent polarization hysteresis responses of the heterostructures. The influence of physical model parameters on the ZnO-BaTiO3-ZnO double Wurtzite-Perovskite characteristics will be presented.
Reference:
[1] Interface-charge-coupled polarization response of Pt-BaTiO3-ZnO-Pt heterojunctions: A physical model approach, V. M. Voora, T. Hofmann, M. Brandt, M. Lorenz, M. Grundmann, N. Ashkenov, and M. Schubert, J. Electron. Mater 37, 1029-1034 (2008).
9:00 PM - C6.15
Broadband Dielectric Spectroscopy of Ruddlesden-Popper series Sr(n+1)Ti(n)O(3n+1) (n= 1, 2, 3) and Multiferroic Thin Films.
Nathan Orloff 1 2 , Wei Tian 3 , James Booth 1 , Ichiro Takeuchi 2 4 , Darrell Schlom 5 , Craig Fennie 6
1 EEEL, NIST, Boudler, Colorado, United States, 2 Physics, University of Maryland, College Park, Maryland, United States, 3 Material Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania, United States, 4 Material Science and Engineering, University of Maryland, College Park, Maryland, United States, 5 Material Science and Engineering, Cornell University, Ithaca, New York, United States, 6 Center for Nanoscale Materials , Argonne National Laboratory , Argonne, Illinois, United States
Show AbstractBroadband permittivity characterization of thin-films is essential for the development of new microwave devices with both low and high frequency applications. Over a broad enough range, frequency dependence encapsulates important physical information about the materials such as domain structure, relaxation, and disorder. We have explored the frequency dependent permittivity of Ruddlesden-Popper series Sr(n+1)Ti(n)O(3n+1) (n= 1, 2, 3) thin films as a function of temperature and dc electric-field. A new on-wafer broadband technique using interdigitated capacitors and coplanar waveguides is exploited to extract frequency response from 500 Hz to 40 GHz. The Ruddlesden-Popper films were deposited on LSAT substrates by MBE. At room temperature, the permittivities obtained for Sr(n+1)Ti(n)O(3n+1) (n= 1, 2, 3) were 42, 54, and 77 respectively and independent of frequency. Electric field tunability occurs at low temperatures (30 K), and suggests that Sr4 Ti3 O10 may develop weak ferroelectricity. Loss tangent for the series members (n= 1, 2, and 3) were below our measurement sensitivity, but are less than Broadband Dielectric Spectroscopy of Ruddlesden-Popper series Sr(n+1)Ti(n)O(3n+1) (n= 1, 2, 3) and Multiferroic thin films4%. We will also present broadband in plane permittivity results for Bi(1-x)Sm(x)FeO3 as a function of composition, temperature and dc electric field.
9:00 PM - C6.16
Studies on the Dielectric and Optical Properties of Epitaxial Multiferroic Pb(Fe0.5Nb0.5)O3 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 synthesized epitaxial multiferroic PbFe0.5Nb0.5O3 (PFN) thin films using pulse laser deposition technique. PFN thin films were grown on (100) oriented MgO substrate with a Lantanum Strontium Cobalt oxide (LSCO) layer deposited as bottom electrode. The PFN deposition parameter (873 K, 250 mJ and 200 mT oxygen pressure) gave single phase perovskite. Dielectric properties were measured as a function of frequency (100 Hz to 1MHz) and temperature (100 K to 650 K). The temperature evolution of the dielectric constant showed diffuse ferroelectric phase transition with frequency dispersion. The dielectric maximum temperature range was 337 K (5 kHz) to 380 K (100 kHz) which make it differ to that of the bulk counterpart suggested strain induced phase transition. The frequency dispersion of dielectric constant follows the Vogel-Fulcher law for relaxor materials which gives activation energy of 0.00971 eV and a freezing temperature of 313 K. Besides the dielectric maxima corresponding to the relaxor ferroelectric phase transition, two more features were observed in the temperature evolution of the dielectric constant of PFN thin films. One is in the vicinity of the Neel temperature (140 K for bulk) where a small peak around 160 K was observed. We believe this dielectric anomaly is due to strong spin-dipole coupling which has been already observed in PFN single crystal. The third anomaly occurs at high temperature (600 K) which is near the Burn temperature. This peak may be related to structural changes in the sample. Temperature dependent Raman spectra were used to investigate structural phase transition. The magnetization behavior displayed weak ferromagnetism.
9:00 PM - C6.17
Investigation of Dielectric and Electrical Properties of Lead Free Relaxor Ba(Ti ,Sn)O3.
Ashok Kumar 1 , Iris Rivera 1 , Rajesh Katiyar 2 , Pritesh Mirchandani 1 , Jose Lopez 1 , Ram Katiyar 1
1 Department of Physics, University of Puerto Rico, San Juan, Puerto Rico, United States, 2 Mechanical Engg., UPR Mayaguez, Mayaguez, Puerto Rico, United States
Show AbstractWe have synthesized lead free relaxor Ba(Ti1-xSnx)O3 (x= 0-0.30) (BTSC) ceramics using conventional solid-state reaction technique and Lead free Ba(Ti1-xSnx)O3 (x< 30%) (BTSF) thin films using sol-gel technique. Broad range dielectric spectroscopy studies of BTSC and BTSF were carried out over a wide range of temperature (~ 100 K-650 K) and frequency 100 Hz to 1MHz. BTSC showed broad dielectric maxima for less than 20 percent of Sn concentration, above this composition, Ba(Ti0.90Sn0.30)O3 (BTSC30) illustrated wide frequency dispersion and dielectric maximum temperature near 190 K. The modified Curie-Weiss law and the non linear Vogel-Fulcher fitting of BTS30 confirmed the relaxor nature of the materials. The dielectric properties of BTSF30 thin films showed broad (almost flat) dielectric maxima over a wide range of temperature. The temperature dependent micro Raman spectra for both films and ceramics suggested anomaly in the integrated intensity and full with at half maxima (FWHM) near the dielectric maximum temperature. The Phonon life time and the relaxation time were calculated near the dielectric dispersion region that suggested slow down in the breathing of the polar nano-regions with decrease in temperature. Impedance spectroscopy is a versatile tool to check the grain and the grain boundary contributions in materials, we employed this technique to investigate bulk and grain boundary resistance/conductance of BTSC and BTSF over a wide range of temperature, especially near the frequency dispersion region. Capacitance vs. applied electric field indicates nonlinear dielectric response for different frequency and temperature. A comparative study of bulk BTS will be carried out with respect to thin films of the same composition
9:00 PM - C6.18
Studies in the Phase Transition and Conduction Mechanisms in the Nanostructured Bi4-xEuxTi3O12 System: An Impedance Spectroscopy Approach.
Jorge Mata 1 , Abril Munro 2 4 , Eduardo Martinez 3 , Jesus Siqueiros 4
1 Fisica, Facultad de Ciencias-Universidad Autonoma de Baja California, Ensenada, B.C., Mexico, 2 Area de Química y Tecnología Química de la Madera. F.I.TEC.MA., , U.M.S.N.H., Morelia, Michoacan, Mexico, 4 Departamento de Materiales Avanzados, CNyN, UNAM, Ensenada, B.C., Mexico, 3 Centro de Investigación en Materiales Avanzados (CIMAV), Parque de Investigación e Innovación Tecnológica (PIIT), Nueva Carretera Aeropuerto Km. 10, CIMAV, Apodaca , N.L., Mexico
Show AbstractDRX patterns show the solubility of Eu up to 12% besides all the samples are single phase. TEM micrographs show the nanostructured nature for the doped samples as a consequence of the mechanochemical activation in the synthesis steps. The inclusion of Eu in the structure is justified due to the lowering of the transition temperature when compared with unmodified BIT. Broadened phase transitions are obtained as a consequence of the chemical inhomogeneities induced by the Eu inclusion. The high permittivity values found for BIT-Eu samples must be explained as arising from Maxwell-Wagner relaxation occurring at the interfaces of grains and grain boundaries where barrier layer capacitances are formed as is suggested in our impedance analyses. Hysteresis loops of modified BIT ceramics reveal leaky behavior at room temperature due to the high space charge density promoted with the earth rare inclusion which is in accordance with the high dielectric losses measurements. Although ferroelectricity is present, low polarization values are obtained due to the appearance of ionic defects that promote strong conduction mechanisms and domain pinning that weakens the long range ferroelectric ordering. The presence of nanostructured complexes produce changes in the electrical behavior due to an increasing of the grain boundary density.
9:00 PM - C6.19
An Anomaly in the Temperature Dependence of the Electromechanical Properties of Gd Doped PZT53/47.
Jorge Portelles 1 2 3 , Raiza Ledezma 2 3 , Juan Fuentes Betancourt 2 , Nelson Suarez Almodovar 1 2 , Oscar Raymond 1 , Jesus Heiras 1 , Jesus Siqueiros 1
1 Centro de Nanocencias y Nanotecnología, Universidad Nacional Autónoma de México, Ensenada Mexico, 2 Facultad de Física-IMRE, Universidad de La Habana, La Habana Cuba, 3 , Instituto de Cibernética, Matemática y Física Aplicada, La Habana Cuba
Show Abstract9:00 PM - C6.20
Piezoelectric Displacement of BiFeO3 Thin Film Measured with Bipolar Applied Field at Liquid Nitrogen Temperature.
Bong-Yeon Lee 1 , Hiromi Shima 2 , Hiroshi Naganuma 2 , Takashi Nakajima 2 , Soichro Okamura 2 , Takashi Iijima 1
1 Resarch Center for Hydrogen Industrial Use and Storage, National Institute of Advanced Industrial Science and Technology, Tsukuba Japan, 2 Department of Applied Physics, Tokyo University of Science, Tokyo Japan
Show AbstractIn recent years, perovskite-type oxide materials including magnetic elements such as BiFeO3, BiMnO3, and TbMnO3, which exhibit ferroelectric and ferromagnetic properties simultaneously, have attracted much attention as the magnetization (and respectively the dielectric polarization) is expected to be modulated by the electric field (and respectively by the magnetic field). This magnetoelectric effect is expected to be the basis of a memory device by a combination of ferroelectric and ferromagnetic properties.BiFeO3 (BFO) is a known multiferroic material and is of particular interest in terms of practical applications, because both its ferroelectric and antiferromagnetic ordering temperatures are well above room temperature (Curie temperature ~ 830 °C and Néel temperature ~ 370 °C). BFO belongs to the perovskite class of materials and could be a good alternative ferro-/piezoelectric material. It is also Pb-free and environmentally preferable.Multiferroic materials show both (anti) ferroelectric order and (anti) ferromagnetic order in the same phase and a coupling between them over a certain range of temperature. Such materials could be electrically polarized by applying an external magnetic field; alternately an external electric field could induce magnetization in them. So multiferroic materials can provide opportunities for potential applications in magnetic as well as ferroelectric devices. We have investigated the piezoelectric characteristics of the BFO thin films that the piezoelectric characteristic was not able to be measured because the leakage was high at the room temperature. BFO thin films were prepared onto Pt/Ti/SiO2/Si substrates using a chemical solution deposition process. We have developed the system using the twin beam laser doppler equipment. The twin beam laser doppler system was able to measure, and to evaluate the polarization and displacement at the same time. Moreover, for suppress the leakage, we have cooled the sample to liquid nitrogen temperature (-190 °C) and used to high speed frequency (100 kHz). And we have gained the ferroelectric properties as remanent polarization (Pr) = 57.3 µC/cm2, coercive field (Ec) = 153 kV/cm at 100 Hz and -190 °C. And the piezoelectric induced displacement-electric field curves shaped like a butterfly was confirmed at 100 kHz and -190 °C.
9:00 PM - C6.21
Study of Antiferromagnetism in Hexagonal RMnO3 (R=Y, Ho, Er) Films and Multilayers by Neutron Diffraction.
Isabelle Gelard 1 , Stephane Pailhes 2 , Sylvain Petit 2 , Charles Simon 3 , Catherine Dubourdieu 1
1 , LMGP, CNRS-GrenobleINP, Grenoble France, 2 , LLB, CEA-CNRS, Gif-sur-Yvette France, 3 , CRISMAT, CNRS, ENSICAEN, Caen France
Show Abstract9:00 PM - C6.22
Complex Structural and Magnetic Ordering in AA'BB'O6 Perovskites.
Graham King 1 , Lora Wayman 1 , Andrew Wills 2 , Patrick Woodward 1
1 Chemistry, The Ohio State University, Columbus, Ohio, United States, 2 Chemistry, University College London, London United Kingdom
Show AbstractWe report the preparation and characterization of a large number of new AA'BB'O6 perovskite type compounds. By using a highly charged d0 cation (W+6) for B' we are able to stabilize a layered ordering of the A-cations in addition to the commonly observed rock-salt ordering of the B-cations. Ordering of the A-cations in stoichiometric perovskites was previously very rare. We have prepared two new series of NaLnBWO6 perovskites, one with B=Mg and another with B=Mn, for all Ln from La-Ho. The variation in the lattice parameters and crystal symmetry across the lanthanide series is discussed. Magnetic susceptibility measurements indicate that the compounds in the series with B=Mn display complex and varied magnetic ordering behaviour. All of them order antiferromagnetically at temperatures ranging from 6-15K. Several of these compounds undergo multiple magnetic phase transitions that involve ordering of both cation sub-lattices. The magnetic structures of the compounds with Ln=La, Nd, and Tb have been determined by neutron diffraction. Incommensurate ordering of the moments is observed when Ln=Nd and Tb. All of the compounds that belong to the series with B=Mg are paramagnetic down to a temperature of 2K, indicating that the ordering of the magnetic moments in the lanthanide layers for the compounds of the B=Mn series is induced by the presence of magnetically ordered cations on the B-lattice.
9:00 PM - C6.23
One-magnon Light Scattering and Spin Reorientation Transition in Epitaxially BiFeO3 Thin Films.
Manoj Singh 1 , Sandra Dussan 1 , Ram Katiyar 1
1 Physics, University of Puerto Rico, San Juan, Puerto Rico, San Juan, Puerto Rico, United States
Show AbstractOne – magnon excitation Raman scattering has been observed in epitaxial BiFeO3 thin films grown on (111) SrTiO3 substrates. The intensities and the frequency of the magnon mode at 18.9 cm-1 (M1) showed a discrepancy at the characteristic temperatures of ~140 and ~200K and the magnon mode at 27.9 cm-1 (M2) disappeared at ~200K suggesting spin-reorientation (SR) transition. The partial spectral weight of the magnon modes is believed to be transferred to the lowest phonon mode appearing at 72.8 cm-1 and magnon mode M2 disappearing near 200K reveal magnon – phonon coupling. The dc susceptibility measurement showed a large discrepancy near these two temperatures evidently elucidating the SR transition mechanism.
9:00 PM - C6.24
Magnetic Properties of Multiferroic BiFeO3-BiCoO3 Solid Solution Films Having MPB Phase.
Hiroshi Naganuma 1 , Shintaro Yasui 2 , Ken Nishida 3 , Hiroshi Funakubo 2 , Takashi Iijima 4 , Soichiro Okamura 5 , Yasuo Ando 1
1 , Tohoku University, Sendai Japan, 2 , Tokyo Institute of Technology, Yokohama Japan, 3 , National Defence Academy of Japan, Yokosuka Japan, 4 , AIST, Tsukuba Japan, 5 , Tokyo University of Science, Tokyo Japan
Show AbstractBi-based multiferroic materials (BiCrO3, BiMnO3, BiFeO3, BiCoO3) have attracted much attention in recent year. Many reports in term of the BiFeO3 have been published due to its high remanent polarization. However spontaneous magnetization can not expect because of G-type of antiferromagntic spin configuration with slight spin canting system. When we use the multiferroic materials for the spintronics application devises such as spin-filter material or spin current source, the materials should possess the ferromagnetic component. We anticipate that if B-sites of iron in BiFeO3 are substituted for the other 3d transition metal, antiferromagntic spin order is breakup and then the spontaneous magnetization appears. In fact, in our previous reports 1) various kinds of 3d transition metals of 5 at.% [Bi(MxFe1-x)O3, x=0.05, M=Cr, Mn, Co, Ni, Cu] were substituted, and it was revealed that the cobalt substitution effectively increased the remanent magnetization (< 1 emu/cm3 → 4 emu/cm3@ RT) as well as magnetic coercivity (≈0 kOe → 2 kOe@ RT). In present study, we increased the cobalt contents of the Bi(CoxFe1-x)O3 films above x=0.05, and discuss the magnetic properties and crystal structure as well as ferroelectricity of the Bi(CoxFe1-x)O3 films. The Bi(CoxFe1-x)O3 (0 ≦ x ≦ 0.33) films were fabricated by MOCVD and CSD methods onto the SrTiO3(100) substrates. The remanent magnetization linearly increased with increasing the cobalt contents, and the maximum remanent magnetization of 35 emu/cm3 was obtained at the cobalt contents of x=0.22. Above x=0.22, the remanent magnetization decreased with increasing the cobalt contents. The shape of M-H curves almost overlapped in perpendicular and parallel to the film plane. This isotropic behavior indicates that iron of B-sites was randomly substituted by cobalt and the spontaneous magnetization was attributed to the local ferromagnetism. We will also evaluate the magnetic anisotropy of epitaxial Bi(CoxFe1-x)O3 films using a ferromagnetic resonance (FMR). The remanent polarization monotonically decrased as the cobalt contents increased, although the electric coercive field was constant. The remanent polarization at x=0.22 was around 30 μC/cm2. According to structural analysis using XRD and Raman spectroscopy, it was revealed that the films were epitaxial grown onto SrTiO3 (100) substrates and the crystal structure changed from the rombohedral structure (R3c) to tetragonal structure (P4mm) at the cobalt contents of x=0.22. This result indicated that appearance of morphotropic phase boundary (MPB) at x=0.22 [Bi(CoxFe1-x)O3, x=0.22]. This means the electric field has a possibility to induce the change of magnetic properties, so-called magneto-electric (ME) effect due to its large displacement driven by MPB. We will discuss the possibility of ME effect of the Bi(CoxFe1-x)O3 film having MPB phase. Ref 1) Hiroshi Naganuma, Jun Miura, Soichiro Okamura, Appl. Phys. Lett. to be publisded (2008).
9:00 PM - C6.25
Magnetic and Electric properties of TbMnO3 doped with Al, Ga and In.
Fatima Perez 1 2 , J. Heiras 2 , J. Siqueiros 2 , L. Salamanca-Riba 1
1 Materials Science and Engineering, University of Maryland, Hyatsville, Maryland, United States, 2 Materiales Avanzados, Centro de Nanociencias y Nanotecnología-Centro de Investigación Científica y de Educación Superior de Ensenada, Universidad Nacional Autonoma de Mexico, Ensenada, Baja California, Mexico
Show AbstractThe simultaneous presence and interaction of magnetic and ferroelectric properties in the same phase of a given material are of high interest from the points of view of the fundamental physics involved and from that of the development of new technological devices. Manganites doped with rare earths are the subject of intensive research because they exhibit strong relation between magnetic and electric ordering in spite of the fact that the phenomena of interest take place at low temperatures (around 40 K). Here we present the results of the study of the mechanisms for the magnetic-electric coupling as a means to increase the operation temperature of these materials. We present the magnetic and electric properties of the Tb1-xAxMnO3 compound where A = Al, Ga and In, and x = 0.05 and 0.1. Samples were synthesized by the powder solid state reaction method producing single phase compounds. SEM analysis exhibits the porous nature of the samples. For samples doped with Ga, magnetic measurements demonstrate the coexistence of weak ferromagnetic and antiferromagnetic ordering just as in compounds doped with Al as previously reported[1]. The magnetic order in these compounds is mainly attributed to the Tb+3 ions just like in the Al doped alloys. The Neel temperature measured is close to 60 K. Electric measurements vs. temperature show that the samples behave like a semiconductor.[1]F. Pérez et al., Phys. Stat. Sol. (c) 4, No. 11, 4049-4053 (2007).This work is supported by NSF MRSEC DMR-00-0520471. It is also partially supported by PAPIIT, Proj. No IN114207, IN102908, and CONACyT 47714-F. F. Pérez acknowledges the support from CONACyT scolarship. We acknowledge the facilities of the Nanoscale Imaging Spectroscopy and properties (NISP) laboratory, the Center for Nanophysics and Advanced Materials (CNAM) and the X-Ray Crystallographic Center at the University of Maryland.
9:00 PM - C6.26
Electric-field-induced Enhancement of the Remnant Magnetization in Epitaxial CoFe2O4 Films Grown on PMN-PT.
Jung Hwan Park 1 , Min G. Kim 2 , Sangwoo Ryu 1 , Hyun M. Jang 1
1 MSE, Postech, Pohang Korea (the Republic of), 2 , Pohang Accelerator Laboratory , Pohang Korea (the Republic of)
Show AbstractSpinel-ferrites have long been the subject of extensive investigations due to their extraordinary magnetic and magnetostrictive properties. Recently, they have brought about intensive scientific investigation because the combinations with piezoelectric materials, such as composite films and multilayers, turned out to be candidates for room-temperature multiferroic structures. Magnetoelectric (ME) coupling effects in these types of multiferroic structures are caused by the interfacial strain: the strain generated by the piezoelectric phase under an applied electric field is coupled to the magnetostrictive phase mechanically, and this consequently changes the magnetic moment. However, the ME coupling effect arising from a layered structure is known to be significantly reduced by the clamping effect exerted by the non-piezoelectric single-crystalline substrate. To overcome this limitation, we have adopted a piezoelectric single-crystalline substrate, 0.72PMN-0.28PT (PMN-PT), which is known to exhibit giant electrostrictive strains. Epitaxial CoFe2O4 (CFO) films were then grown by pulsed laser deposition on (001) planes of these substrates. The Fe K-edge in the CFO layer was examined by employing extended x-ray absorption fine structure (EXAFS) spectroscopy under dc electric field. This study clarifies the ME coupling arising from the piezoelectric-magnetostrictive effect in atomic scale. In addition to this, we have shown the intrinsic coupling between ferroelectric and ferromagnetic order parameters through the enhancement of magnetization under an applied electric field. We suggest this type of bi-layer structures can significantly enhance the degree of the ME coupling by an electric-field control of the remanent magnetization.
9:00 PM - C6.27
Magnetocapacitance Study of PMN-35PT and Terfenol-D Multilayers Grown by Pulsed Laser Deposition.
B. Ramachandran 1 , B. Neela Sekhar 1 , Mamidanna Rao 1
1 Department of Physics, Materials Science Research Centre and Nano Functional Material Technology Centre , Indian Institute of Technology Madras, Chennai, Tamil Nadu, India
Show Abstract9:00 PM - C6.28
Ferroelectric Domains and Switching Behaviors of Room-temperature Multiferroic (Ga,Fe)2O3 Epitaxial and Polycrystalline Thin Films.
Ji Hye Lee 1 , William Jo 1 , Morgan Trassin 2 , Nathalie Viart 2
1 Physics, Ewha Womans University, Seoul Korea (the Republic of), 2 Institute of Physics and Chemistry of Materials of Strasbourg, CNRS, Strasbourg France
Show AbstractWe report ferromagnetic and ferroelectric characteristics of multiferroic Ga2-xFexO3 (0.8 < x < 1.4) thin films that have been epitaxially grown on conductive indium tin oxide (ITO) coated yttrium stabilized zirconia (YSZ) substrates and Pt/TiO2 coated Si substrates by pulsed laser deposition (PLD). We furthermore present the crystallographic relationships between the films and the substrate. The thin films show a perfect epitaxial growth and their magnetic properties are close to those of the bulk [1]. The films are ferromagnetic and for x = 1.4, the Curie temperature is above room temperature (370 K), while presenting a saturation magnetization of 90 emu/cm3 at 300 K. It is difficult to justify ferroelectric properties because the empty d states condition necessary for ferroelectric properties clashes with the need for d electrons in order to have a spin moment in multiferroic. Therefore to clarify their exotic multiferroic characteristics is requiring a careful measurement of ferroelectric properties. We observed local ferroelectric domain structures and retention behaviors of the thin films through scanning force microscopy (SFM). We applied a reverse-poling scheme in order to investigate switching characteristics of the thin films [2]. Local poling behaviors of the ferroelectric domains were observed as a function of time in both single-poled and reverse-poled regions. Also, hysteresis loops of the thin films were obtained by SFM in various regions. Through these investigations, we quantified not only space charge density but also the bound charge density of the thin films. [1] M. Trassin, N. Viart, G. Versini, J.-L. Loison, J.-P. Vola, G. Schmerber, O. Cregut, S. Barre, G. Pourroy, J. H. Lee, W. Jo and C. Meny, Appl. Phys. Lett. 91, 202504 (2007).[2] J. H. Lee, T. Y. Kim, M. R. Choi, Y. J. Oh and W. Jo, Appl. Phys. Lett. 91, 072906 (2007).
9:00 PM - C6.29
Ferroelectric/Ferromagnetic Core/Shell Nanoparticles Towards Multiferroics.
Yong Koo 1 , Jong Jung 1
1 Physics, Inha University, Incheon Korea (the Republic of)
Show AbstractContrary to previously reported composite multiferroics, e.g. heterostructure thin films, we have investigated the cross-coupled phenomena such as magnetoelectric and magnetodielectric properties in ferroelectric core and ferromagnetic shell nanoparticles. Our core/shell nanoparticles are composed of ~500 nm size BaTiO3 encapsulated by ~50 nm size Fe3O4. Near the structural transition temperatures of core BaTiO3, magnetization and magnetoresistance of shell Fe3O4 clearly show several kinks due to the structure transition induced strain. Below Verwey transition temperature, we have observed negative magnetodielectric property with smooth curvature, and attributed it to the strong spin-lattice coupling and its modification near core/shell interfaces.
9:00 PM - C6.3
Growth and DC Conductivity Studies of Tripotassium Sodium Dichromate Single Crystal.
Georgekutty Joseph 1 , Santhosh Kumar 2 , Godfrey Louis 3
1 Department of Physics, Sacred Heart College,Thevara, Cochin, Kerala, India, 2 School of Pure and Applied Physics, Mahatma Gandhi University, Kottayam, Kerala, India, 3 Department of Physics, Cochin University of Science and Technology, Cochin, Kerala, India
Show Abstract9:00 PM - C6.30
Magnetoelectric Coupling and Magnetic Anisotropy in Nanostructured Oxide Thin Films.
Steven Crane 1 , Christoph Bihler 2 , Yoon Seok Oh 3 , Hyeong-Jin Kim 3 , Sebastian Goennenwein 4 , Kee Hoon Kim 3 , Martin Brandt 2 , R. Ramesh 1 5
1 Materials Science and Engineering, University of California, Berkeley, Berkeley, California, United States, 2 Walter Schottky Institut, Technische Universität München, Garching Germany, 3 Physics and Astronomy, Seoul National University, Seoul Korea (the Republic of), 4 Walther-Meissner-Institut, Bayerische Akademie der Wissenschaften, Garching Germany, 5 Physics, University of California, Berkeley, Berkeley, California, United States
Show AbstractMagnetoelectric thin film nanostructures are interesting for their possible ability to limit power consumption and enable new types of electronic device control. We report direct observation of magnetoelectric coupling in two separate systems comprised of CoFe2O4 and NiFe2O4 pillars embedded in a ferroelectric BiFeO3 matrix through quasi-static and resonance techniques. Additionally, we show that the NiFe2O4 nanostructures can be tuned magnetically by altering the aspect ratio of the pillars through a thickness series and by changing the average pillar spacing through a composition series. The magnetic anisotropy is studied using vibrating sample magnetometry and ferromagnetic resonance, which show that the uniaxial magnetic anisotropy in the growth direction changes sign upon increasing the film thickness. The magnitude of this anisotropy contribution can be explained via a combination of shape and magnetostatic effects, using the object-oriented micromagnetic framework (OOMMF).
9:00 PM - C6.31
Magnetoelectric Properties of Pulsed Laser Deposited Ba0.7Sr0.3TiO3/La0.67Sr0.33MnO3 Heterostructures.
Ricardo Martinez 1 , Shojan Pullockaran 1 , Jaime Reniel Calzada 1 , Sushil Singh 2 , Ratnakar Palai 1 , Ram Katiyar 1
1 Physics, University of Puerto Rico, San Juan, Puerto Rico, United States, 2 Solid State , Physics Laboratory, Delhi , Timarpur, India
Show AbstractFerroelectric barium strontium titanate Ba0.7Sr0.3TiO3 (BSTO) with Tc of 312K has extensively been investigated for ferroelectric random access memory (Fe-RAM) and tunable microwave device applications because of its low dielectric loss and high tunability under an external electric field. Meanwhile, La0.67Sr0.33MnO3, a colossal magnetoresistive manganite (ferromagnetic transition temperature of 312K with high degree of spin polarization), is a potential candidate for spintronic device applications. The combination ferroelectric-ferromagnetic in thin film form can produce an artificial magnetoelectric multiferroic with novel magnetoelectric properties. It is also expected to have innovative effects and new functionalities if the magnetic and ferroelectric orders can be coupled in ferroelectric-ferromagnetic heterostructures, which are the building block of the current memory devices. The multilayer heterostructures of BST/LSMO have been fabricated on Pt/Si and SrTiO3 substrates by pulsed laser deposition. The X-ray diffraction and Raman spectroscopy measurements of heterostructures showed single phase with high degree of crystallinity. The dielectric measurements with function of temperature of trilayer (LSMO/BSTO/LSMO) heterostructures (~12 nm each layer) showed very sharp drop in dielectric permittivity and loss at 200 and 310K. The heterostructures with SrRuO3 as bottom electrode showed drop in dielectric permittivity and loss at 150, 200, and 310K. The drop at 150K can be related to the ferromagnetic transition temperature of SRO, whereas the drop at 310K can be related to the ferromagnetic and ferroelectric transition temperature of LSMO and BSTO, respectively. The drop at 200K is not yet fully understood. The results of magnetoelectric measurements also very interesting and will be discussed in details. Keywords: Ferroelectric, manganites, multilayer, heterostructure.
9:00 PM - C6.32
Charge Driven Magnetoelectric Coupling in a Ferromagnetic / ferroelectric Bilayer.
Hajo Molegraaf 1 2 , Jason Hoffman 3 , Carlos Vaz 3 , Charles Ahn 3 , Jean-Marc Triscone 2
1 Faculty of Science and Technology, University of Twente, Enschede Netherlands, 2 Département de Physique de la Matière Condensée, University of Geneva, Genève Switzerland, 3 Department of Applied Physics, Yale University, New Haven, Connecticut, United States
Show Abstract9:00 PM - C6.33
Exchange Bias Development in LSMO/BFO Multilayers.
David Kirkwood 1 , Jiwei Lu 1 , Stuart Wolf 1
1 , University of Virginia, Charlottesville, Virginia, United States
Show AbstractMeta-Multiferroics promise to bring the full functionality of coupled ordered state materials to the forefront of device research. We focus on the development of composites coupling the magnetic and electronic order in LSMO and BFO respectively. This study examines thin film multilayer growth of these materials using pulsed laser and pulsed electron deposition techniques. We have deposited multilayers with a varied ratio of film thicknesses to examine the influence of thickness ratio and film stress on the exchange coupling at the interface.
9:00 PM - C6.34
Observation of Magnetoelectric Effect and Tuning of Ferromagnetic Resonance Frequency using Bilayers Formed of Bulk YIG and PMN-PT.
Jacob Leach 1 , Vitaliy Avrutin 1 , Umit Ozgur 1 , Hadis Morkoc 1
1 , Virginia Commonwealth University, Richmond, Virginia, United States
Show Abstract9:00 PM - C6.35
Quantitative Determination of the Enhanced Magnetoelectric Coupling in BiFeO3-CoFe2O4 Nanostructures.
Yoon Seok Oh 1 , Hyeong-Jin Kim 1 , Steven P. Crane 2 , Seongsu Lee 3 , R. Ramesh 2 , Sang-Wook Cheong 3 , Kee Hoon Kim 1
1 School of Physics & Astronomy, Seoul National University, Seoul Korea (the Republic of), 2 Department of Materials Science and Engineering, University of California, Berkeley, California, United States, 3 Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey, United States
Show AbstractWith growing interest worldwide toward utilizing multiferroic materials for novel memory and sensor devices, there have been numerous efforts to synthesize multiferroic thin films with large magnetoelectric coupling. Toward this direction, for example, a nanostructure BiFeO3-CoFe2O4 film with SrRuO3 electrodes, in which nanopillars of CoFe2O4 are embedded in a host matrix film of BiFeO3, has been reported as a promising approach to improve the magnetoelectric coupling via enhancement of the strain coupling between the two components. As yet, quantitative information on the magnetoelectric susceptibility (MES) of the nanostructure film is still lacking because it has been difficult to measure a reduced magnetoelectric signal due to small electrode size and tiny thickness in spite of a strong magnetoelectric coupling in thin film samples. In the present work, we present quantitative MES data for a BiFeO3-CoFe2O4 nanostructure film (300 nm thick), a BiFeO3 thin film (250 nm thick), and a BiFeO3 single crystal. For the measurements, we have developed a highly sensitive MES measurement system operating in cryogenic (down to 2 K) and high magnetic field (H) environments (up to 9 T). We find that the MES of the BiFeO3-CoFe2O4 nanostructure shows an anti-symmetric shape with the dc H, as expected in magnetoelectric materials with large strain coupling. Moreover, the MES response becomes anisotropic with the change of H- directions. When H- and electric polarization directions are perpendicular, the MES of the nanostructure becomes as high as 1×10-10 s/m at relatively low H=1.4 T, while those of the pure BiFeO3 thin film and single crystal show a quasi-linear increase up to 9 T. We further demonstrate that at a fixed temperature and H, the MES value of the nanostructure is larger by approximately one order of magnitude than that of a pure BiFeO3 film, and by two orders of magnitude than that of a single crystal of BiFeO3.
9:00 PM - C6.36
Magnetoelectric Effect in Patterned PZT/LSMO Bilayers Grown by RF Sputtering.
Emmanuel Rowe 1 , Bo Xiao 1 , Umit Ozgur 1 , Vitaliy Avrutin 1 , Hadis Morkoc 1
1 Electrical Engineering, Virginia Commonwealth University, Richmond, Virginia, United States
Show Abstract9:00 PM - C6.37
The Si-Epitaxial Oxide Interface: Atomic Structure via Synchrotron Diffraction and First Principles.
Yaron Segal 1 , Fred Walker 1 , James Reiner 1 , Alexie Kolpak 1 , Sohrab Ismail-Beigi 1 , Charles Ahn 1 , Zhan Zhang 2
1 Applied Physics and Center for Research on Interface Structure and Phenomena, Yale University, New Haven, Connecticut, United States, 2 Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractThe successful integration of crystalline ferroelectric and multiferroic oxides with covalent semiconductors requires atomic level control over the structure of the interface structure between the two materials. Silicon and Barium Oxide are representatives of the two classes of materials that form this problem. BaO was grown epitaxially on Si using a sub-monolayer strontium interfacial passivation layer. We present a structure determination of this interface using X-Ray synchrotron radiation and first principles calculations, supported by RHEED and TEM data. We observe a unique phenomenon in which the Si surface's 2X1 symmetry continues into the BaO film, creating a non-cubic 2X1 phase of BaO near the interface. The structural effect of different interface stoichiometries was examined using DFT calculations. Comparison with the X-Ray diffraction data demonstrates the interface is O-rich. Theoretically predicted distortions of the bulk structures of Si and BaO in this interface accurately agree with experimental data.
9:00 PM - C6.38
Nonlinear Optical Spectroscopy and Domain Imaging in Multiferroic BiFeO3 .
Amit Kumar 1 , Sava Denev 1 , Mariola Ramirez 1 , Jon Ihlefeld 1 , Darrell Schlom 1 , Lane Martin 2 , Ying-Hao Chu 2 , Ramamoorthy Ramesh 2 , Joe Orenstein 3 , Alexander Litvinchuk 4 , Janice Musfeldt 5 , Venkatraman Gopalan 1
1 Materials Science and Engg., Pennsylvania State University, University Park, Pennsylvania, United States, 2 Materials Science and Engg., University of California Berkeley, Berkeley, California, United States, 3 Materials Science Divison, Lawrence Berkeley National Lab, Berkeley, California, United States, 4 , University of Houston, Houston, Texas, United States, 5 Department of Chemistry, University of Tennessee, Knoxville, Tennessee, United States
Show AbstractIn this work, we have used non-linear second harmonic generation (SHG) spectroscopy as a function of temperature, to analyze the optical response due to many magnons in BiFeO3. A new type of SHG spectral resonance based on electric dipole (ED) transitions due to multi-magnon processes has been established. The temperature evolution of the observed 2- and 3-magnon sidebands reveals an overall intensity decrease of ~50% on approaching TN, opposite to the non-resonant energies which remain almost constant up to 725 K [1]. We also employ confocal second harmonic and Raman imaging to study domain structures in BiFeO3. The work highlights the sensitivity of multimagnon spectroscopy to analyze spin-charge coupling in multiferroics that has been minimally explored so far and appears to be broadly applicable to other multiferroics and magnetoelectrics.
[1] “Spin-Charge-Lattice Coupling through Multi-Magnon Excitations in Multiferroic BiFeO3” arXiv:0803.3473 (March 2008)
9:00 PM - C6.39
Optical Second Harmonic Generation Probing of Strained CaTiO3 Thin Films.
Eftihia Vlahos 1 , Amit Kumar 1 , Sava Denev 1 , Charles Brooks 1 , Darrell Schlom 1 , Carl-Johan Eklund 2 , Karin Rabe 2 , Craig Fennie 3 , 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 Center for Nanoscale Materials, Argonne National Laboratory, Argonne , Illinois, United States
Show AbstractFirst principles calculations have predicted strained CaTiO3 thin films to be ferroelectric with a spontaneous polarization of up to ~0.5C/m2. Optical second harmonic generation (SHG) and symmetry analysis of the polarization studies has determined the point group of 2.5 % strained CaTiO3/(110) DyScO3 thin films to be mm2. Temperature dependent measurements were undertaken and yield a transition temperature of ~ 150 K. Electric-field induced domain switching studies are also presented.
9:00 PM - C6.4
Polarization Switching in BiScO3-PbTiO3 Thin Films.
Paula Vilarinho 1 , Jingzhong Xiao 1 , Aiying Wu 1
1 Department of Ceramics and Glass Engineering, University of Aveiro, Aveiro Portugal
Show AbstractRecently, (1-x)BiScO3-xPbTiO3 (BSPT) ferroelectric films have attracted considerable attention as promising materials for applications in microelectromechanical systems, memory devices, and more recently nanoelectromechanical devices in high temperature environment.[1] Compared to the common ferroelectric Pb(Zr,Ti)O3 (PZT), morphotropic phase boundary (MPB) BSPT system exhibits a higher Curie temperature (Tc) of about 450 degree Celsius (100 degree Celsius higher than PZT) and comparable properties to those of relaxor-PbTiO3, meeting the requirements for ferroelectrics with high-Tc for applications in automotive and aerospace industry, among others.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 oxide electrodes [3]. A room temperature dielectric constant, εr >1500 and dielectric loss, tanδ 0.02 were obtained at 100 Hz. A well-defined hysteresis loop was observed with a remanent polarization, Pr ~23 μC/cm2 and a remarkable low coercive field, Ec ~33 kV/cm. Additionally the leakage current of these films was considerably decreased from more than two orders of magnitude (10-9 A) when oxides electrodes (IrO2) were used.It is well known that ferroelectric films fabricated on Pt/TiO2/SiO2/Si substrates have serious problems of reliability (namely fatigue), affecting their performance and limiting their utilization. The fatigue behaviour, denoted by the reduction of switchable polarization accompanied by the decay in the remanent polarization of a ferroelectric as a function of the switching cycles, restrains dramatically the life of ferroelectric based memory devices. However the fatigue behaviour of BSPT films is still not studied. The major objective of this work is to characterise the ferroelectric fatigue behaviour of MPB 0.37BiScO3-0.63PbTiO3 thin films prepared by sol-gel. The fatigue of unseeded and seeded BSPT films on Pt and oxide electrodes (IrO2 and LaNiO3) was characterized. The obtained results indicate that BSPT films show no fatigue for > 10-9 cycles, which points to excellent reliability performance over PZT/Pt films (apparent fatigue behaviour after 10-6 cycles). Supported by Transmission Electron Microscopy and Rutherford Backscattered Spectroscopy studies, the role of the interface film / electrode as a source of the degradation of the switching behaviour is discussed. Special attention was paid to the oxygen vacancy migration and electron injection into the film. 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, Electrical properties of sol-gel derived MPB 0.37BiScO3-0.63PbTiO3 thin films deposited on iridium oxide electrodes, submitted.
9:00 PM - C6.41
Investigations of the Influence of Ferroelectric Polarization on Magnetic Anisotropy in Thin Film Heterostructures of Ferromagnetic Cobalt/ferroelectric P(VDF-TrFE).
Abhijit Mardana 1 , A. Baruth 1 , C. Mart 2 , Stephen Ducharme 1 , S. Adenwalla 1
1 Department of Physics & Astronomy & Nebraska Center for Materials and Nanoscience, University of Nebraska-Lincoln, Lincoln, Nebraska, United States, 2 Department of Physics, Utah State University, Logan, Utah, United States
Show AbstractThe study of the interaction between ferromagnetic and ferroelectric films provides exciting physics as well as the potential for applications in magnetic data storage and random access memory devices. We have undertaken the investigation of the interaction in thin film heterostructures of transition metal ferromagnets (FM) and polymer ferroelectrics (FE), specifically poly (vinylidene fluoride with trifluoroethylene) [P(VDF–TrFE)], to look for changes in the magnetic anisotropy of the ferromagnetic layer that have been predicted to occur on switching the ferroelectric polarization. [1] The expected change in magnetic anisotropy is small and confined to the ferroelectric/ferromagnetic interface; hence a carefully designed experiment is necessary. Our samples consist of [glass/ Pt (50 nm)/Co/ferroelectric P(VDF-TrFE) (53 nm)/Al (30nm)]. The Co layer is wedge-shaped, ranging in thickness from 5-22 Å, covering the range of Co thicknesses over which the magnetic anisotropy transitions from in-plane to out-of-plane. [2] The metallic layers are deposited through shadow masks to form the top and bottom electrodes. The polymer ferroelectric films are deposited by the Langmuir-Blodgett technique, resulting in films with superior crystalline and ferroelectric properties. [3] The magnetic and ferroelectric layers of the samples have been carefully characterized using the Magneto-Optical Kerr Effect (MOKE) and the pyroelectric effect, respectively. The Co wedge is characterized by both polar and longitudinal MOKE at 2 mm steps along the total length of 40 mm from thin edge to thick edge to allow for determination of the point at which the magnetization transitions from out-of-plane to in-plane and the top Al electrode is deposited in this region. The calculated magnetic anisotropy changes resulting from the reversal of ferroelectric polarization are tiny-on the order of 1 erg/cm2-and probing this transition region gives us the best chance of seeing the effect of the polarization. The MOKE loop is measured for both positive and negative ferroelectric polarization of the P(VDF-TrFE) film and any differences in the two MOKE loops is ascribed to the change in magnetic anisotropy of the ferromagnetic layer. The expected small changes are difficult to see in this dc experiment. We are in the process of developing an ac technique, in which we switch between the two polarizations states of the ferroelectric at a magnetic field close to the coercive field of the ferromagnet. This is complicated by the slow switching times of the ferroelectric polymer. Results of both sets of measurements will be reported. This research work is supported by the NSF MRSEC program through Grant No. DMR-0213808. References: 1. Chun-Gang Duan et al, Appl. Phys. Lett. 92, 122905 (2008) 2. P. F. Carcia, J.Appl. Phys. 63, 5066 (1988) 3. A. V. Bune, et al, Nature (London) 391, 874 (1998).
9:00 PM - C6.42
Basic Design and Experimental Verification of Multi-Ferroic Sensor by Combining Magnetostriction and Piezoelectric Effect.
Naoyuki Hosokawa 1 , Yoshiyuki Hayashi 2 , Tasuku Kon 3 , Chihiro Saito 4 , Teiko Okazaki 5 , Yasubumi Furuya 6
1 Graduate Student, Hirosaki university, Hirosaki Japan, 2 Graduate Student, Hirosaki university, Hirosaki Japan, 3 R&D Division , Rivereletec Co.Ltd, Nirasaki Japan, 4 NJC Research Center, Namiki Precision Jewel Co.,Ltd,, Tokyo Japan, 5 Physical Science , Hirosaki University, Hirosaki Japan, 6 Intelligent Machines and System Engineering, Hirosaki University, Hirosaki Japan
Show AbstractAn ideal sensor/actuator material has high sensitivity, high response speed, high energy conversion efficiency and integrated smartness having a sensor/actuator functions simultaneously. As one of such a high performance and multi-functional materials and devices, the category of multi-ferroics materials is gathering strong interest in material science and engineering field. The basic concept and category of ferroic and multi-ferric materials are mentioned briefly, and technical importance of multi-ferroic approach for designing advanced multi-functional sensors /actuator based on a mutual coupling effect between each ferroic material elements will be pointed out for intelligent/smart technology. In the present paper, two types of multi-ferroic sensor/actuator devices designed by combination of magnetostriction and piezoelectric effect, i.e. (1) magnetically driven composite sensor/actuator and (2) a surface acoustic wave (SAW) sensor sensitive to a magnetic field are presented.First, a large-scale robust bulk composite sensor/actuator is designed to combining the ferromagnetic magnetostriction of FePd, FeGaX (Galfenol) alloys and piezoelectric plates of PZT. . The composite is laminated and sensor characteristics of sensitivity etc. are investigated for 1) changing the volume fraction of each element and anisotropy of the constituent crystalline materials, 2) response speed in the alternative magnetic field.As a result, a clear improvement of sensor sensitivity seems higher with increasing the volume fraction of magnetostrictive alloy, but the combination of each crystalline anisotropy of the elements and optimum volume fraction should be studied in more detail.Secondarily, multi-functionally designed, multi-ferroic senor device using surface acoustic wave (SAW) will be introduced. Piezoelectric LiTaO3(x-y cut) base materials were used. IDT( pitch= 20μm) was produced by lithography. In this case, on the surface part between IDTs, environmentally active material films of magnetostrictive alloys of Galfenol FeGaX(X=Al) or FePd are formed by magnetron-sputtering. Various environmental sensing parameters i.e. temperature, magnetic field strength, stress-strain etc. can be evaluated nondestructively and wirelessly from the signal analysis of amplitude and phase change of SAW, which indicates the effectiveness of our proposed multi-functional SAW device sensor . Consequently, these results show the effectiveness and engineering possibility of new type of multi-functional composite actuator and sensor based on multi-ferroic effect.
9:00 PM - C6.43
Magnetoelectric Coupling in All Thin Film Magnetoelectric Sensors.
Peng Zhao 1 , Zhenli Zhao 2 , Dwight Hunter 1 , Richard Suchoski 1 , Chen Gao 2 , Scott Mathews 3 , Manfred Wuttig 1 , Ichiro Takeuchi 1
1 Department 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 Department of Electrical Engineering and Computer Science, Catholic University of America, Washington D.C., District of Columbia, United States
Show AbstractPrototype ac magnetic field sensors operating at room temperature based on all thin film magnetoelectric (ME) devices have been fabricated. The ME layers consist of a sol-gel derived Pb(Zr0.52Ti0.48)TiO3 (PZT) film and a sputter deposited magnetostrictive Fe70Ga30 film. The bilayer structures are fabricated on back-etched Si wafers, and the laser cutting technique has been implemented to release and isolate the cantilevers with patterned devices for optimization of the sensor performance. The PZT layer and the Fe70Ga30 layer couple via the piezoelectric d31 mode and the ME coupling coefficient is as high as ≈ 920 mV/(Oe cm) for a 1 mm x 1mm device at the mechanical resonant frequency of the cantilever. The Fe70Ga30 film is relatively soft magnetically, and only requires dc bias magnetic field of around 70 Oe. The interface between the PZT and the FeGa films is studied by SEM. The clamping effect on the ME coupling is studied by varying the thickness of the Si substrates. The scale effect is investigated by changing effective areas of the capacitors on the devices. The sensitivity of the ac magnetic field detection will also be reported. The present work indicates presence of robust ME coupling in microfabricated multilayer thin film ME devices, which would readily facilitate future integration of the device with various electronic components as well as development of novel sensor array systems.
9:00 PM - C6.44
Exchange Coupling Across the La0.7Sr0.3MnO3 and BiFeO3 Interface.
Pu Yu 1 , Mark Huijben 1 2 , Micky Holcomb 1 , Chan-Ho Yang 1 2 , Lane Martin 2 , Ying-Hao Chu 3 , Rong Yu 4 5 , Jason Hoffman 6 , Charles Ahn 6 , Seiji Yunoki 4 5 , Shuai Dong 4 5 , Maria Daghofer 4 5 , Satoshi Okamoto 5 , Adriana Moreo 4 5 , Silvia Picozzi 7 , Elbio Dagotto 4 5 , Ramamoorthy Ramesh 1 2
1 Department of Physics, University of California, Berkeley, California, United States, 2 Department of Materials Science and Engineering, University of California, Berkeley, California, United States, 3 Department of Materials Science and Engineering, National Chiao Tung University, TsinChu Taiwan, 4 Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee, United States, 5 Material Science and Technology Division, Oak Ridge National Lab, Oak Ridge, Tennessee, United States, 6 Department of Applied Physics, Yale University, New Haven, Connecticut, United States, 7 INFM - Dip. Fisica, Univ. L’Aquila, Coppito (L’Aquila) Italy
Show Abstract9:00 PM - C6.45
Dynamic Observation of the Strain-mediated Magnetoelectric Coupling Effect.
Sung Hwan Lim 1 , Todd Brintlinger 1 , Yi Qi 1 , John Barry 2 , John Melngailis 2 , Manfred Wuttig 1 , John Cumings 1 , Ichiro Takeuchi 1 , Lourdes Salamanca-Riba 1
1 Materials Science and Engineering, University of Maryland, College Park, Maryland, United States, 2 Electrical and Computer Engineering, University of Maryland, College Park, Maryland, United States
Show AbstractDynamic observation of the strain-mediated magnetoelectric (ME) coupling effect was pursued by applying an external electric (E) field to a Fe0.7Ga0.3/BaTiO3 (Fe-Ga/BTO) TEM sample using Lorentz imaging mode in a TEM. We present not only the first direct observation of strain-mediated coupling between a piezoelectric material and a ferroelectric material, but also a new method for studying ME effect using in-situ Lorentz TEM. An epitaxial piezoelectric BTO layer followed by a polycrystalline magnetostrictive Fe-Ga layer were synthesized by pulsed laser deposition and magnetron sputtering, respectively. To apply an electric field in-plane, Fe-Ga was patterned into electrodes on BTO using electron-beam lithography. To remove the substrate clamping, the BTO layer was released from the SrTiO3 substrate using focused ion beam milling. The BTO film had a saturation polarization of Ps = 17 μC/cm2. The magnetic domain structure was observed dynamically using Lorentz TEM. Domain walls were observed to move either by applying a magnetic field (~ 200 Oe in-plane) or by applying an electric field (~ 100 kV/cm). When the electric field is used, strain propagation may also be observed, confirming a strain-mediated ME effect.This work was supported by NSF-MRSEC under grant No. DMR 0520471, ARO 28D1083899, and ONR-MURI N000140610530. We acknowledge the use of the TEMs in the Nanoscale Imaging Spectroscopy and Properties (NISP) laboratory at the University of Maryland a SEF of our MRSEC.
9:00 PM - C6.46
Probing Defect Effect on Local Bias-Induced Phase Transitions: Hysteresis Loop Fine Structure in Piezoresponse Force Microscopy.
Stephen Jesse 1 , Brian Rodriguez 1 , Maxim Nikiforov 1 , Sergei Kalinin 1 , Eugene Eliseev 2 , Anna Morozovska 3
1 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Institute for Problems of Materials Science, National Academy of Science of Ukraine, Kiev Ukraine, 3 V. Lashkaryov Institute of Semiconductor Physics, National Academy of Science of Ukraine, Kiev Ukraine
Show AbstractThe development of piezoresponse force spectroscopy has opened the pathway for probing the local bias-induced phase transitions, including ferroelectric and ferroelastic polarization switching, antiferroelectric-ferroelectric phase transitions, and the broad spectrum of bias-induced transitions between ergodic, non-ergodic, and ferroelectric phases in relaxors. The unique advantage of these measurements is that the phase transition is induced locally by the field confined by a conductive probe. Hence, the effect of the local structural and surface defects can be probed on an individual defect level provided that defect size and/or defect-defect spacing is large compared to the probe size (10-20 nm). The characteristic signature of the defect-domain interaction is the formation of the fine structure in the PFM hysteresis loop. In this presentation, summarized are several examples of the hysteresis loop fine structure due to polarization switching in the vicinity of localized and extended structural defects. Notably, spectroscopic imaging in many cases allows significant increase of spatial resolution (below 5 nm) as compared to PFM resolution on the same sample (~20 nm). The origins of this resolution enhancement are discussed. Quantitative interpretation of the data requires the development of non-local models for the tip-defect interactions, achieved through the combination of analytical Ginzburg-Landau based theory. The pathways for interpretation of multidimensional experimental data based on the neural network fitting are discussed. Research supported by the Center fro Nanoscale Materials Sciences, Basic Energy Sciences, U.S. Department of Energy at Oak Ridge National Laboratory, which is managed by UT-Battelle, LLC.
9:00 PM - C6.47
Magnetoelectric Properties of BiFeO3/La0.67Sr0.33MnO3 Heterostructures.
Shojan P Pullockaran 1 , Ricardo Martinez 1 , Jaime Reniel Calzada 1 , Singh Sushill 2 , Ratnakar Palai 1 , Ram S Katiyar 1
1 Physics, University of Puerto Rico, San Juan PR, Puerto Rico, United States, 2 Solid State, Physics Laboratory, Delhi , Timarpur, India
Show AbstractBiFeO3 (BFO) is one of the most widely studied multiferroics because it is only single-phase multiferroic at room temperature i.e an antiferromagnetic (AF) incommensurate phase with cycloidal modulation (λ=60nm) below 370oC, Ferroelectric up to ~820 οC, and ferroelasticity between 820-930 οC. The current interest in multiferroics is largely based on engineered epitaxial and heterostructured thin films because of their physical properties being as good as bulk and their technological applications in data storage, magnetic recording, spintronics, quantum electromagnets, and sensors. Devices made up of multiferroic materials can perform more than one task and facilitate device miniaturization. The epitaxial thin films grown on SrTiO3 substrates have high value of polarization (~100 μC/cm2) compared to the best-known ferroelectrics (PZT, BSTO, and BLTO). The higher leakage current and the poor magnetic properties of BFO are the bottleneck for practical applications. Meanwhile, La0.67Sr0.33MnO3, a colossal magnetoresistive manganite (ferromagnetic transition temperature of 312K with high degree of spin polarization), is a potential candidate for spintronic device applications. The combination of ferroelectric-ferromagnetic in thin film form can produce an artificial magnetoelectric multiferroic with innovative effects, new functionalities and novel magnetoelectric properties if the magnetic and ferroelectric order parameters can be coupled in heterostructures, which are the building blocks of the current memory devices. In order to enhance the magnetoelectric properties of BFO, we fabricated multilayer heterostructrures of BFO/LSMO (with different layer thickness of each layer from 10-100nm) on Pt/Si and SrTiO3 single crystal substrates with SrRuO3 as bottom electrode. X-ray diffraction and Raman spectroscopy measurements of heterostructures showed each layer having single phase and high degree of crystallinity. The dielectric permittivity and loss measurements of trilayaer heterostructures on Pt/Si substrates with SRO bottom electrode with function of temperature showed sharp drop at 270 and 310K. The later one could be related to the ferromagnetic transition temperature of LSMO, whereas the former, as yet, is not well understood. However, it may relate to a new magnetic phase transition or change in the magnetic ordering in BFO. The magnetoelectric properties of different heterostructures will be discussed in details. Keywords: Multiferroics, manganites, multilayer, heterostructure.
9:00 PM - C6.48
Lead-free Piezoelectric Thin Films for MEMS Applications.
Seung-Hyun Kim 1 2 , Chang Young Koo 1 , Miso Kim 2 , Woo Sik Kim 2 , Jowoong Ha 1 , Brian Wardle 2
1 R&D Center, INOSTEK Inc., Ansan, Gyeonggi, Korea (the Republic of), 2 Dept. of Aeronautics and Astronautics, MIT, Cambridge, Massachusetts, United States
Show AbstractThere is a strong interest in introducing ferroelectric thin films for applications in microelectromechanical systems (MEMS) since they have large piezoelectric coefficients and electromechanical coupling coefficients. Among ferroelectrics, PZT films are considered the most promising candidates for the piezoelectric MEMS devices since they can produce high mechanical strain under applied electric field. Recently there have been a number of concepts presented for bio-medical devices using piezoelectric thin films. Some applications need insertion of the device into the body for operation and treatment. Even if PZT has various excellent properties, specific medical devices require bio-compatible lead-free piezoelectric thin films. For these applications, we have investigated (Na,K)NbO3 (NKN) thin films using chemical deposition method. To develop NKN films for these applications, it is necessary to have a comprehensive knowledge regarding the mechanisms contributing to the observed piezoelectric and the related electrical properties. To achieve more systematic evidences and to make reliable properties of piezoelectric thin films for bio-medical applications, we have performed a study based on the experimental results of the piezoelectric and dielectric properties of NKN films. Here, we describe the piezoelectric properties of bio-compatible NKN thin films and real bio-medical device performance in detail.
9:00 PM - C6.49
Artificially Designed Multiferroic Pb(Zr,Ti)O3/Cofe2O4 Nanostructured Thin Films.
Nora Ortega 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 Abstract9:00 PM - C6.5
Measurement of Ferroelectric Properties of Polycrystalline BiFeO3 Films using a High Driving Frequency of 100 kHz System.
Hiroshi Naganuma 1 , Yosuke Inoue 2 , Soichiro Okamura 2
1 , Tohoku University, Sendai Japan, 2 , Tokyo University of Science, Tokyo Japan
Show AbstractHigh remanent polarization and a high piezoresponse values were recently reported in the BiFeO3 film and bulk, which has been a driving force to study the ferroelectricity of the BiFeO3 film as well as opens an avenue to study the host BiFeO3 film for the various functional device applications. However, because of the high leakage current in the polycrystalline BiFeO3 films, the ferroelectric hysteresis loops show an unsaturated expanded shape at room temperature, and it is necessary to decrease the measuring temperature for reducing the leakage current in order to obtain the ferroelectric hysteresis loop with high squareness in general. In the present study, we demonstrated a measuring system using the high driving frequency of 100 kHz [FCE-1A type] produced by TOYO Corporation for the leaky polycrystalline BiFeO3 films and evaluated the remanent polarization as well as coercive field at room temperature. BiFeO3 films were fabricated on the Pt/Ti/SiO2/Si(100) substrates by a chemical solution deposition (CSD) followed by a post-deposition annealing at 723 K for 10 min in air. After annealing, a top Pt electrode was deposited by an electron beam evaporation. The film thickness of the BiFeO3 film was about 180 nm. Formation of the single phase of polycrystalline BiFeO3 film was identified by a conventional θ/2θ x-ray diffraction pattern and a transmission electron microscopy (TEM) observation. The ferroelectric hysteresis loops using the low frequency of below 1 kHz showed expanded shapes, which is attributed to effect of leakage current component. When using the high frequency of 100 kHz system, the ferroelectric hysteresis loops of high squareness with a twofold remanent polarization of 114 μ/cm2 and the coercive field of 0.55 MV/cm was obtained even at room temperature due to the reduction of influcence of leakage current component. This result indicated that high frequency system is useful method to check ferroelectricity for the high leaky materials such as BiFeO3 film. However, when using the high driving frequency of 100 kHz measurement system, a phase delay of around a few hundred nsec occurred between applied voltage and polarization component. The reliability of the measurement system has not discussed yet. Therefore, we confirmed accuracy of the high driving frequency of 100 kHz system by comparing the remanent polarization using a positive, up, negative and down (PUND) measurements.1) We also measured the ferroelectric hysteresis loops by 100 kHz and PUND for the polycrystalline Pb(Zr,Ti)O3 films having low leakage current, and discussed accuracy of the high driving frequency of 100 kHz system. The cause of the phase delay between applied voltage and polarization component will be also discussed.Ref. 1) Hiroshi Naganuma, Yosuke Inoue, and Soichiro Okamura, ‘Evaluation of electrical properties of leaky BiFeO3 films in high electric field region by high-speed PUND measurement’ Applied Physics Express, 1, 061601 (2008).
9:00 PM - C6.50
Large Area Ba1-xSrxTiO3 Thin Films for Microwave Applications Processed by Pulsed Laser Deposition.
Chakrapani Varanasi 1 , K. Leedy 2 , D. Tomich 2 , Guru Subramanyam 3
1 , University of Dayton Research Institute (UDRI), Dayton, Ohio, United States, 2 , Air Force Research Laboratory, WPAFB, Ohio, United States, 3 , University of Dayton, Dayton, Ohio, United States
Show AbstractBa1-xSrxTiO3 (BST) thin films with x=0.4 or x=0.5 were deposited on 75 mm diameter Si wafers in a large area pulsed laser deposition chamber enabling full-wafer device fabrication using standard lithography. Since the substrate to target distance is high (~10 cm) in large area chambers as compared to small chambers, the processing parameters were re-optimized to get good quality films with uniform thickness. Processing parameters such as laser scanning speed across a 2” diameter target, rep rate, laser energy were optimized to obtain high quality films. X-ray diffraction and microstructural analyses on the BST films grown on Pt/Au/Ti electrodes deposited on SiO2/Si wafers revealed films with (110) preferred orientation with grain size < 100 nm. An area map of the thickness and crystal orientation of a BST film deposited on SiO2/Si wafer also showed (110) preferred orientation with a film thickness variation < 4%. BST films were found to have a large dielectric tunability of 76% at an electric field of 400 kV/cm and dielectric loss tangent below 0.03 at microwave frequencies up to 20 GHz.
9:00 PM - C6.51
Radiation of X-rays in Low-Pressure Gas Using LiNbO3 Single Crystal.
Shinji Fukao 1 , Yoshikazu Nakanishi 1 , Tadahiro Mizoguchi 1 , Yuuki Sato 1 , Yoshiaki Ito 2 , Shinzo Yoshikado 1
1 Faculty of Science and Engineering, Doshisha University, Kyotanabe, Kyoto, Japan, 2 Institute for Chemical Research, Kyoto University, Uji, Kyoto, Japan
Show Abstract9:00 PM - C6.6
Improved Dielectric Properties of Multilayered Thin Films of (Ba0.6Sr0.4)TiO3/MgO Doped (Ba0.6Sr0.4)TiO3.
Kwang-Hwan Cho 1 2 , Chong-Yun Kang 1 , YoungPak Lee 2 , Seok-Jin Yoon 1
1 Thin Film Materials Research Center, KIST, Seoul Korea (the Republic of), 2 q-psi and BK21 Dept. of Physics, Hanyang Univ., Seoul South Africa
Show AbstractFerroelectric BaxSr1-xTiO3 (BST) thin films are being considered as an excellent candidate for microwave tunable devices because they have a high dielectric constant, a low dielectric loss, a low leakage current and high tunability in compared with general dielectric materials. However in general, for epitaxial BST films, a large tunability is observed in the films that have a large dielectric loss and a small tunability in the films that have a low dielectric loss. The major issue for pure BST thin films is to reduce the dielectric loss while maintaining a large tunability. Therefore, a tradeoff between the high tunability and large dielectric loss exists in the pure BST thin films incorporated into microwave tunable devices. Large tunabilities are highly required because the degree of phase shifting ability is directly related to tunability, and insertion loss is inversely related to the tunability. Therefore, the larger the tunability is, the stronger phase shifting ability is, and the smaller the insertion loss is. A low dielectric loss is very desirable to decrease the insertion loss and, hence loss. Furthermore, reducing the dielectric loss is also beneficial to expanding the operating frequency of the device. To date, several group’s researches have shown that the multilayered and spuerlattice structural BST films could remarkably increased the tunability of BST thin films and the additions of some dopants (with small concentrations) such as Fe2+, Mn2+, Mg2+, Ni2+, and La3+ into pure BST thin films could dramatically reduce the dielectric loss of BST thin films. The mechanism for lowing the dielectric loss by addition of some dopants centers on the thesis that ions with a charge less than +4 can substitute for Ti+4 and behave as electron acceptors. These acceptors present the reduction of Ti+4 to Ti+3 by neutralizing the donor action of oxygen vacancies. It is also noticed that the dielectric tuning decreases with addition of acceptor dopants in BST films. Considering the tradeoffs between tunability and the value of dielectric loss, dielectric constant, and film’s resistivity, the concentrations of the acceptor dopants must be optimized to obtain the best overall properties for use in tunable device applications. In this study, the multilayered BST/MgO doped BST (BSTM) films have been fabricated and the dielectric properties have also been compared with pure BST and BSTM films. The crystallographic properties of BST, BSTM, and BST/MgO doped BST the films were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM) and field emission scanning electron microscope (FESEM). The dielectric properties, capacitance and dielectric Q (1/ tanδ) of BST, BSTM, and BST/MgO doped BST the films were measured using a symmetrical stripline resonator with shorted ends. The dielectric constants of the films were calculated using a partial capacitance method at 1~3 GHz.
9:00 PM - C6.7
Textured PbSrTiO3 Thin Films and Their Ferroelectric Fatigue Behaviors under Varying Switching Pulse Widths and Frequencies.
Eduardo Martinez 1 2 , Oscar Blanco 2
1 , Centro de Investigacion y Materiales Avanzados (CIMAV), Apodaca, Nuevo Leon, Mexico, 2 Centro de Investigación en Materiales, DIP-CUCEI, Universidad de Guadalajara, Guadalajara, Jalisco, Mexico
Show AbstractWe have investigated the switching properties of ferroelectric lead strontium titanate (PbxSr1-x)TiO3 (PST) capacitors using epitaxial La0.5Sr0.5CoO3 (LSCO) electrodes to evaluate their potential application for non-volatile memory applications (NVFRAMS). PST thin films were prepared by RF-Ion Sputtering Technique. Structures of the films were analyzed by x-ray diffraction, atomic force microscopy (AFM) and scanning tunneling microscopy (STM). The electrical performance of the PST based capacitors grown on epitaxial LSCO substrates were evaluated through Polarization-Voltage (P-V) and Fatigue measurements. At an applied voltage of 4V, the films showed good hysteresis loops with remnant polarization (Pr), saturated polarization (Ps) and coercive voltage (Vc) of 5.11 μC/cm2, 15.2 μC/cm 2 and 1.1 V respectively. The <001> preferentially oriented PST ferroelectric capacitor did not show a decrease in polarization up to 108 switching cycles at an applied voltage of 4 volts and a frequency of 100 kHz. It is proposed that the good performance of the PST capacitors can be attributed to the high degree of orientation of the PST films in the <001> direction induced by the epitaxial LSCO film. Fatigue tests were also carried out systematically by varying the switching pulse width with a fixed duty cycle and with a fixed switching period, respectively. A gradual increase followed by an abrupt increase of the fatigue rate was observed with the increase of the switching pulse width. Field-induced defect diffusion was used to explain the results.
9:00 PM - C6.9
Investigation of the Conduction Mechanism in (1-x)Bi(Ga0.05Fe0.95)O3-xPbTiO3 Solid Solutions.
Guiyang Shi 1 , Jianguo Chen 1 , Yufa Qi 1 , Shengwen Yu 1 , Jinrong Cheng 1
1 School of Materials Science and Engineering , Shanghai University, Shanghai China
Show Abstract
Symposium Organizers
Charles Ahn Yale University
Philippe Ghosez Universite de Liege
Masashi Kawasaki Tohoku University
Darrell Schlom Cornell University
Jean-Marc Triscone University of Geneva
C7: Strain-induced Ferroelectricity
Session Chairs
Wednesday AM, December 03, 2008
Room 210 (Hynes)
9:30 AM - C7.1
Competition Between Polar Ground State and Octahedral Rotation in Epitaxially Strained LaAlO3.
Alison Hatt 1 , Nicola Spaldin 1
1 Materials, University of California, Santa Barbara, California, United States
Show AbstractWe investigate the effect of epitaxial strain on [001] oriented LaAlO3 by performing density functional calculations within the local density approximation. We find that in the absence of AlO6 octahedral rotations, compressive strain produces large polarizations but that a non-polar distorted state with cooperativeoctahedral rotations can accomodate the large strains at a lower energy cost. When we tune the applied strainfrom compressive to tensile we observe a transition from space group I4/mcm to Fmmm, corresponding to two distinct patterns of octahedral tilting and rotation.
9:45 AM - C7.2
Phase-field Simulation of Domain Stabilities and Structures in Strained SrTiO3 Thin Films.
Guang Sheng 1 , Jingxian Zhang 1 , Yulan Li 1 , Samrat Choudhury 1 , Darrell Schlom 1 , Quanxi Jia 2 , Zi-Kui Liu 1 , Long-Qing Chen 1
1 Department of 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 AbstractStrontium titanate (SrTiO3) is known as a classical example of a system with coupled structural and incipient ferroelectric instabilities. In this study, the antiferrodistortive transition and ferroelectric transition in a strained (100) SrTiO3 thin film are analyzed using phase-field approach. Based on the simulation results, the misfit strain-temperature domain stability diagrams, graphical representation of stable ferroelectric and structural domain structures as a function of strains and temperature, are constructed. The misfit strain-misfit strain domain stability diagrams at several representative temperatures were also generated, and the corresponding domain structures were analyzed and compared with experimental studies. By taking into account the different domain structures obtained from the variations of Landau coefficients used in the simulation, it is expected that such diagrams will provide guidance for interpreting experimental measurements and observations as well as to the design of SrTiO3 films with specified domain structures.
10:00 AM - C7.3
Structural Boundary Conditions for Ferroelectrics.
Fred Walker 1 , Yaron Segal 1 , J. Reiner 1 , A. Kolpak 1 , Zhan Zhang 2 , S. Ismail-Beigi 1 , C. Ahn 1
1 Applied Physics, Yale University, New Haven, Connecticut, United States, 2 Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractElectrical boundary conditions are critical in affecting the stability of ferroelectricity, especially for the establishment of an out-of-plane polarization in very thin films. The detailed atomic structure between the film and the substrate can also strongly influence the stability of the ferroelectric ground state. In this work, we determine the interface structure of thin films of coherent SrTiO3 grown epitaxially on silicon, with a SrTiO3 thickness between two and five unit cells. Using synchrotron x-ray scattering, we show how the details of the epitaxial interaction between the silicon and SrTiO3 film can induce an out-of-plane polarization. In particular, we find that the initial layers of oxide on silicon are polar, inducing a polarization in the SrTiO3 film. This polarization is not switchable, however, resulting in a polar, non-ferroelectric ground state for the SrTiO3 film. These results are corroborated by first-principles calculations, which offer insight into the polar nature of strained SrTiO3 grown on silicon.
10:15 AM - C7.4
Epitaxial-strain-induced Ferroelectricity in CaTiO3 from First Principles.
Carl-Johan Eklund 1 , Craig Fennie 2 , Karin Rabe 1
1 Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey, United States, 2 School of Applied and Engineering Physics, Cornell University, Ithaca, New York, United States
Show AbstractFirst-principles calculations for the phonon dispersion of cubic perovskite high-symmetry reference structure of CaTiO3 show a strong polar instability in addition to the zone-boundary oxygen-octahedron instabilities that generate the nonpolar bulk ground-state structure. In this talk, we report the results of a first-principles investigation of low-energy alternative structures of CaTiO3. In particular, we examine the effect of (001) and (111) epitaxial strains on the relative stability of different structures, and consider the possible realization of a epitaxial-strain-induced transition to a ferroelectric phase. The relationship of the theoretical results to available experimental data on epitaxially strained CaTiO3 films will be discussed.
10:30 AM - C7.5
The Role of Strontium in Oxide Epitaxy on Silicon (001).
James Reiner 1 , Kevin Garrity 2 , Fred Walker 1 , Sohrab Ismail-Beigi 1 2 , Charles Ahn 1 2
1 Applied Physics, Yale University, New Haven, Connecticut, United States, 2 Physics, Yale University, New Haven, Connecticut, United States
Show AbstractThe ability to grow crystalline SrTiO3 on the silicon (001) surface, developed in the last decade, enables the integration of crystalline oxides and semiconductors for both technological applications and fundamental scientific inquiries. This promise is related to the wide range of behavior exhibited by crystalline oxides, including magnetism, ferroelectricity, superconductivity, and colossal magnetoresistance. 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. The transition layer between the semiconductor and crystalline oxide is an alkaline earth metal, most often strontium, that is deposited on the silicon surface at around 650°C. This strontium sub-monolayer forms ordered surface structures that have been extensively studied, both experimentally and theoretically. Despite this attention, inconsistencies have persisted between experimental results and theoretical predictions for this surface structure. Motivated by a desire to resolve these questions and develop a fundamental understanding of this important transition layer between silicon and oxide, we have studied the structures strontium forms on the surface of miscut silicon wafers, which, unlike the regular silicon wafers, have a unique surface termination. These experiments avoid ambiguities in surface symmetry and reveal an unexpected reaction of strontium with the silicon surface. This reaction rearranges the top layer of silicon to replace the original top layer with strontium at high temperatures. At low temperatures, this reaction is suppressed, leading to a different, but symmetry related, surface structure. Although all previous approaches to oxide epitaxy on silicon have required high temperature, we find that crystalline oxides can be grown on a clean silicon surface without the need to heat the wafer above 100°C.
10:45 AM - C7.6
Optical Second Harmonic Generation Probing of Strain-Enabled Multiferroicity in EuTiO3 Thin Films.
Eftihia Vlahos 1 , Amit Kumar 1 , Sava Denev 1 , Jon Ihlefeld 1 , June Hyuk Lee 1 , Tassilo Heeg 1 , Darrell Schlom 1 , Xianglin Ke 2 , Peter Schiffer 2 , Karin Rabe 3 , Craig Fennie 4 , Venkatraman Gopalan 1
1 Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania, United States, 2 Department of Physics, Pennsylvania State University, University Park, Pennsylvania, United States, 3 Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey, United States, 4 , Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractStrained-induced multiferroicity from an antiferromagnetic-paraelectric phase to a ferroelectric-ferromagnetic phase has been predicted in EuTiO3 thin films.1 This is confirmed in this presentation. Here we used optical second harmonic generation to probe the ferroelectricity in such films. Symmetry analysis of the obtained SHG polarization studies predict a predominantly mm2 point group for 1.2% tensile strained EuTiO3/(110)DyScO3 thin film, with polarization directions along the <100>p directions of the substrate (p- for pseudocubic). Temperature dependent studies determine the ferroelectric transition temperature to be ~120K. Magnetic measurements suggest a ferromagnetic transition temperature at ~3.3K. First principles predictions show that this system is ideal for studying strain-enabled control of polarization (magnetism) with magnetic (electric) fields for intermediate strain states.1 Phys. Rev. Lett. 97, 267602 (2006)
11:30 AM - C7.7
Employing Uniform Reversible Film Strain from a Piezoelectric Substrate to Examine Effects of Strain in Epitaxial Oxide Thin Films.
Michael Biegalski 1 , Hans Christen 1 2 , Dae Ho Kim 2 3 , Kathrin Doerr 4
1 Center for nanophase materials science, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 3 Department of Physics, Tulane University, New Orleans, Louisiana, United States, 4 Institute for Metallic Materials, Tulane University, IFW Dresden, Dresden, Germany
Show Abstract11:45 AM - C7.8
A New Phase of CaTiO3 Grown Epitaxially on [111] Oriented LaAlO3 Substrates with PLD-RHEED.
Jeroen Blok 1 , Xin Wan 1 , Gertjan Koster 1 , Guus Rijnders 1 , Dave H.A. Blank 1
1 MESA+ Institute for Nanotechnology, University of Twente, Enschede Netherlands
Show AbstractIn this contribution, we will show that controlled growth of CaTiO3 on [111] LaAlO3 is achievable with atomically sharp interface between film and substrate. In general, perovskite thin films grown on [111] surfaces with an atomically sharp interface are rare, because the [111] surface is polar and some sort of surface reconstruction can be expected. In the [111] direction, LaAlO3 consists of LaO33- planes and Al3+ planes. To achieve single terminated substrate surfaces, NaOH solution was used to etch away the Al3+, which resulted in a LaO33- surface termination. We studied the growth of CaTiO3 films on LaAlO3 substrates using Pulsed Laser Deposition with in-situ reflection high-energy electron diffraction (RHEED). Most notably, the initial growth is influenced by the polar substrate surface, as observed by the different first oscillation in the RHEED signal. Transmission Electron Microscopy (TEM) images of this interface show that indeed some kind of reconstruction has formed near the film -substrate interface and that the first monolayer of the CaTiO3 thin film grows anomalously. Surprisingly, the subsequent CaTiO3 layers seem to be strained according to the in-plane lattice parameters of the LaAlO3 substrate. By growing a LaAlO3 buffer layer on the substrate, the interface was improved and resulted in a regular first RHEED oscillation followed by slow damping of subsequent oscillations, suggestive of a more perfect layer-by-layer growth. TEM imaging confirmed that the interfaces between the LaAlO3 substrate, the LaAlO3 buffer layer and the CaTiO3 film are now atomically sharp. Additionally, in the TEM image there is a big difference in contrast between the LaAlO3 substrate and buffer layer. This is probably due to point defects in the LaAlO3 buffer layer, stabilizing the polar [111] surface of the LaAlO3. Both TEM measurements and XRD measurements confirm that the CaTiO3 film is fully strained to the LaAlO3 substrate surface. By growing CaTiO3 on a [111] LaAlO3 substrate, we expect to stabilize the ferroelectric rhombohedral R3c phase of CaTiO3, which was found to be an alternative low energy structure in the first principles calculations of Eklund, Fennie and Rabe (unpublished).
12:00 PM - C7.9
Competition Between Interface Stability and Ferroelectricity in Ultrathin SrTiO3 Films on Silicon.
A. Kolpak 1 , F. Walker 1 , J. Reiner 1 , C. Ahn 1 , S. Ismail-Beigi 1
1 Center for Research on Interface Structures and Phenomena and Department of Applied Physics, Yale University, New Haven, Connecticut, United States
Show AbstractThe successful growth of SrTiO3 on silicon opens up numerous possibilities for the integration of functional oxide properties such as ferroelectricity for non-volatile field effects in field effect transistors and other electronics devices. Due to the epitaxial strain in Si-SrTiO3 thin film structures, it has been suggested that SrTiO3 itself may become ferroelectric on silicon substrates. Using density functional theory calculations we demonstrate that while the chemical interactions at the Si-SrTiO3 interface induce a polar ground state in the SrTiO3 film, the same interactions preclude the existence of ferroelectricity (i.e., a switchable polar state) in films of less than 6 unit cells. This effect is expected to persist into the region of film thickness in which SrTiO3 begins to relax. Changes in the atomic structure and composition of the interface are shown to affect the magnitude and direction of the interface polarity, but we demonstrate that the lack of switchable polarization is independent of interface composition over a wide range of thermodynamically stable compositions. Our results provide insight into the nature of the abrupt transition between a covalently bonded material and an ionically bonded material. Furthermore, they suggest that successful integration of a ferroelectric oxide with silicon will require a mechanism to overcome the intrinsic stability of the interface.
12:15 PM - C7.10
Relaxor Behavior and Polarization Buildup in Compressively Strained Single Crystal SrTiO3 Thin Films.
Ho Won Jang 1 , Chad Folkman 1 , Seung-Hyub Baek 1 , Amit Kumar 2 , Chris Nelson 3 , Michael Biegalski 4 , Darrell Schlom 5 , Xiaqing Pan 3 , Long-Qing Chen 2 , Venkatraman Gopalan 2 , Chang-Beom Eom 1
1 Materials Science and Engineering, University of Wisconsin , Madison, Wisconsin, United States, 2 Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania, United States, 3 Materials Science and Engineering, University of Michigan, Ann Arbor , Michigan, United States, 4 Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 5 Materials Science and Engineering, Cornell University, Ithaca, New York, United States
Show Abstract12:30 PM - C7.11
Effect of Strain on the Piezoelectric Response of Epitaxial xPb(Mg1/3Nb2/3)O3 –(1-x)PbTiO3 Thin Films.
Seung Hyub Baek 1 , Chang-Beom Eom 1 , Venu Vaithyanathan 2 , Jingxian Zhang 2 , Long-Qing Chen 2 , Darrell Schlom 3
1 Materials Science and Engineering, UW-Madison, Madison, Wisconsin, 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 Abstract Relaxor ferroelectrics such as Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN-PT) are very attractive material for sensors and actuators due to their large piezoelectric responses at low driving voltage. However, this large piezoelectric property for a given device geometry is also related to the mechanical boundary conditions i.e., strain and the clamping effect of the substrate. Thus, understanding the effect of the mechanical boundary conditions on the piezoelectric property is very crucial in terms of maximizing the piezoelectric responses for device applications. In order to exploit the effect of strain on piezoelectric response, we have grown high-quality epitaxial PMN-PT/SrRuO3 heterostructure with various thicknesses of the PMN-PT layer using off-axis sputtering. We used two different substrates; (001) SrTiO3 for compressive strain and (001) Si with an epitaxial SrTiO3 overlayer for tensile strain. We have determined the compositions, structures, strain states, piezoelectric coefficients and dielectric constant of the PMN-PT thin films. We will discuss the role of mechanical boundary conditions on the piezoelectric response, which will help to guide the geometrical design of electromechanical devices for optimal performance.
12:45 PM - C7.12
Antiferrodistortive/Ferroelectric Phase Transitions and Correlated Properties in Compressively-strained Epitaxial SrTiO3 Films.
Tomoaki Yamada 1 2 , Alexander Tagantsev 2 , Hiroyuki Ohsumi 3 , Shigeru Kimura 4 , Takafumi Kamo 1 , Hitoshi Morioka 5 , Kazuo Shinozaki 6 , Nava Setter 2 , Hiroshi Funakubo 1
1 , Tokyo Institute of Technology, Yokohama Japan, 2 , Swiss Federal Institute of Technology, EPFL, Lausanne Switzerland, 3 , RIKEN SPring-8 Center, Hyogo Japan, 4 , Japan Synchrotron Radiation Research Institute, Hyogo Japan, 5 , Bruker AXS, Yokohama Japan, 6 , Tokyo Institute of Technology, Meguro-ku Japan
Show Abstract Mechanical coupling between thin films and their substrates strongly influences the properties of the film. Good examples are SrTiO3 epitaxial films, for which a strong modification of the dielectric response by the induced strain has been theoretically and experimentally documented[1-3]. Haeni et al [2] showed a hundreds degree increase of the Curie-Weiss temperature (thus, introduced ferroelectricity) in strained SrTiO3, demonstrating a spectacular example of this effect. In addition to the order parameter posing the ferroelectric phase transition in strained SrTiO3 films, there is another order parameter, resulting in an antiferrodistortive structural phase transition. Although it has been rarely studied, the latter phase transition can also be strongly affected by the strain in the film [4,5]. In unstrained bulk SrTiO3, the temperature of the ferroelectric and antiferrodistortive instabilities differs by some 100 K; for this reason, the antiferrodistortive phase transition hardly affects the dielectric properties of the material. However, in strained SrTiO3 films, these instabilities can be brought closer to each other. This can lead to an appreciable impact of the antiferrodistortive phase transition on the dielectric properties of the strained films. We here address the aforementioned transitions in compressively-strained epitaxial SrTiO3 films deposited on various substrates [(110)NdGdO3, (100)LSAT and (100)LaAlO3] by pulsed laser deposition using synchrotron x-ray diffraction (XRD) at SPring8 (beam line BL02B1) and a laboratory XRD system with 2D detector (Bruker AXS). The anomaly in the temperature dependence of the out-of-plane lattice constant due to these transitions was observed by heating the deposited films from 10K to 600K. The antiferrodistortive phase transition temperature estimated from the measurements was somewhat higher than that theoretically predicted. At the same time, its trend over the strain and the size of the lattice distortions by those phase transitions corresponded to the theoretical predictions. To study the impact of both order parameters on the dielectric properties of compressively-strained SrTiO3 films (unlike the films with tensile strain reported by Haeni and Vasudevarao), the epitaxial SrTiO3 films were grown on (100)CaF2 substrate; which has about twice larger thermal expansion coefficient than that of SrTiO3. In this system, one can strain the films using the thermal stress rather than the lattice mismatch. As a result, one can obtain strongly compressed films, which are rather thick and deposited onto bottom electrodes. Further details are shown in the presentation.[1] N. A. Pertsev et al, Phys. Rev. B 61, R825 (2000); 65, 219901(E) (2002).[2] J. H. Haeni et al., Nature (London) 430, 758 (2004).[3] T. Yamada, et al., Phys. Rev. Lett. 96, 157602 (2006).[4] F. He, et al., Phys. Rev. Lett. 94, 176101 (2005).[5] A. Vasudevarao, et al., Phys. Rev. Lett. 97, 257602 (2006).
C8/V10: Joint Session: Device Applications of Multiferroics
Session Chairs
Wednesday PM, December 03, 2008
Room 210 (Hynes)
2:30 PM - **C8.1/V10.1
Ferroelectric Random Access Memory as a Non-volatile RAM in Multimedia Storage System.
Kinam Kim 1 , Dong Jin Jung 1
1 Memory business division, Samsung Electronics Co. LTD., Yongin-City, Gyunggi-Do, Korea (the Republic of)
Show AbstractThanks to the bi-stable state of ferroelectrics at near ambient temperature, ferroelectric memory has two important characteristics worth mentioning from the operational point of view. First, since core circuitry for the memory does not require stand-by power during quiescent state and the information remains unchanged even with no power supplied, it is thus non-volatile. Second, as the core needs to return the original state after being read, it is called a destructive read-out device. This is because the original information is destroyed after READ. As a consequence, it is essential to return the information back to its original state. This operation is so inevitable in the destructive read-out memory that ferroelectric cell capacitors cannot help suffering frequently from repeated polarization reversals. In particular, when the ferroelectric memory are used as one of the storage devices in computing system, such as byte-addressable memory, the memory has to ensure lifetime memory endurance, which is regarded as the number of READ/WRITE cycles that memory can withstand before loss of any of entire bit information.In the mean time, over the past decades, there has been enormous improvement in VLSI technology to implement system performance of computing platform in many ways. For instance, data throughput of CPU has been increased by thousand times faster than that emerged in the beginning of 1980s. By contrast, state-of-the-art HDD transfers data at 600 MB/sec. Note that data rate of the latest HDD is still orders of magnitude slower than those of the processor/system-memory. To achieve the throughput performance in more effective way, it is therefore needed to bridge performance gap in between each component. On one hand, to compensate the gap between CPU and system memory, CPU cache has been required and adopted. On the other, various technologies have been taken into account to bridge the gap between the system memory and the HDD. In this paper, authors are trying to attempt not only how FRAM provides multimedia storage system such as SSD with performance benefits but also what should be satisfied in terms of reliability in doing so.We demonstrate that FRAM is very eligible to become a non-volatile cache solution, providing benefits both of performance and of reliability. In performance, FRAM cache allows us to rid overhead of power-off recovery in flash translation layer: random WRITE performance has been improved by 250%. Utilizing FRAM as NV-RAM cache could also eliminate FLUSH, which is essential to ensure data integrity in a conventional type. In reliability, in order for FRAM to become NV-RAM cache in such system, what should be overcome is assertion of endurance cycles of 1e15. In line with this, we present what integration technology plays a critical role in achieving 1e15, which is scrutinized systematically and probed by statistical approaches applied to fatigue-data analysis in the latest FRAM.
3:00 PM - **C8.2/V10.2
Development of Mass Production System and Process for Ferroelectric Films.
Koukou Suu 1 , Takehito Jimbo 1
1 Institute for Semiconductor Technologies, ULVAC, Inc., Susono, Shizuoka, Japan
Show AbstractAs for ferroelectric, pyroelectric-sensor etc. that use the bulk material have been used from of old as the functionality device. Recently, the range of use such as ferroelectric random access nonvolatile memories (FeRAM), piezoelectric inkjet printers, the blurring prevention sensors of camera, has extended greatly by developing the ferroelectric thin film. Especially, the miniaturization of all devices is expected from the low power consumption operation, and various developments are advanced. The most typical material is Pb(Zr, Ti)O2 (PZT), but the control of composition and crystalline of PZT thin films were very difficult so far. Moreover, it greatly influences the process, the back and forth such as upper and lower electrodes and the barrier films. We first developed the mass production for FeRAM with the PZT thin film by RF magnetron sputtering, and succeeded in the achievement of uniformity in the wafer, reproducibility and reliability of PZT thin films. Afterwards, the high temperature etching and the MOCVD technology had been developed as next generation FeRAM mass production. Moreover, piezo-electric MEMS mass production technology development has been done at the same time by applying the technology of the mass production sputter tool of FeRAM. In this study, we introduce these ferroelectric device mass production device and processing technology development.
3:30 PM - **C8.3/V10.3
Magnetoelectric Effects in Micro/nanofabricated all Thin Film FeGa/piezoelectric Multilayer Structures.
Ichiro Takeuchi 1
1 Materials Science and Engineering, University of Maryland, College Park, Maryland, United States
Show AbstractWe have fabricated various magnetoelectric (ME) ultilayer structures based on magnetron sputtered FeGa films. The films sputtered onto room temperature Si/SiO2 substrates are polycrystalline as determined by TEM and microdiffraction with a typical grain size on the order of 10s of nm. Magnetostriction of various composition Fe1-xGax films were measured using the cantilever technique, and the lambda100 values extracted are 150~180 ppm for 0.2
4:00 PM - C8/V10:DEV
BREAK
4:30 PM - **C8.4/V10.4
PZT based Ferroelectric Materials for Next Generation Mass-Production FRAM.
Takashi Eshita 1 , Wensheng Wang 1 , Osamu Matsuura 1 , Hideki Yamawaki 1 , Satoru Mihara 1 , Yoshihiro Sugiyama 2
1 FRAM Process Engineering, Fujitsu Microelectronics Limited, Kuwana Japan, 2 Embedded Memories Department, Fujitsu Laboratories Limited, Atsugi Japan
Show Abstract5:00 PM - **C8.5/V10.5
Media Material Challenges for Probe based Memory Device.
Qing Ma 1 , Quan Tran 1 , Nathan Franklin 1 , Valluri Rao 1
1 Components Research, Intel, Santa Clara, California, United States
Show Abstract5:30 PM - **C8.6/V10.6
8Mb 1T-1C Ferroelectric Memory Array Embedded within a 130nm Logic Process.
K. Udayakumar 1 , T. Moise 1 , S. Summerfelt 1 , J. Rodriguez 1 , K. Remack 1 , H. McAdams 1 , S. Madan 1
1 Analog Technology Development, Texas Instruments Inc., Dallas, Texas, United States
Show AbstractC9: Poster Session: Fundamental Properties of Multiferroics
Session Chairs
Thursday AM, December 04, 2008
Exhibition Hall D (Hynes)
9:00 PM - C9.1
Comparison of the Atomic and Electronic Structure of Single F-centers in Cubic PbZrO3, PbTiO3, and SrTiO3 Perovskites.
Yuri Zhukovskii 1 3 , Sergej Piskunov 1 3 4 , Eugene Kotomin 1 3 , Donald Ellis 2 3
1 Inst. of Solid State Physics, University of Latvia, Riga Latvia, 3 Materials Research Center, Northwestern University, Evanston, Illinois, United States, 4 Dept. of Theoretical Chemistry, Univ. of Duisburg-Essen, Essen Germany, 2 Dept. Physics & Astronomy, Northwestern University, Evanston, Illinois, United States
Show AbstractBeneficial properties of partially covalent ABO3-type perovskite materials can be obtained by means of deliberate deviation of oxygen content from the ideal stoichiometry, leading to useful applications in sensors, fuel cells, and microelectronic devices. F- centers, normally described as neutral oxygen vacancies, thus continue to be the subject of intense theoretical and experimental research. In the present work we present and analyze first-principles calculations using a hybrid density-functional-theory on defective perovskites, employing Gaussian-type basis functions localized on atomic nuclei and vacancy sites. Periodic supercells were utilized to minimize vacancy- vacancy interactions in both bulk and surface, thus characterizing their local electronic properties. In comparing results for PbZrO3, PbTiO3, and SrTiO3 in the high-temperature cubic phase, we are able to identify and quantify the crucial role played by metal-oxygen covalency in differentiating the F-center formation energies, lattice distortions, related energy levels and charge distributions.
9:00 PM - C9.10
Lateral Size & Thickness Dependence in Ferroelectric Nanostructures Formed by Localized Domain Switching.
Nathaniel Ng 1 , Rajeev Ahluwalia 1
1 Materials Theory & Simulation Laboratory, Computational Materials Science, Institute of High Performance Computing, Singapore Singapore
Show AbstractFerroelectric nanostructures can be formed by local switching of domains in applications such as piezo-force microscopy (PFM) as well as in patterned electrodes at nanoscale dimensions. Understanding lateral size effects is important to determine the minimum feature size for writing ferroelectric nanostructures. To understand these lateral size effects, we use the time-dependent-Ginzburg-Landau equations to simulate localized switching of domains for a PFM type and parallel-plate capacitor configuration. We show that fringing electric fields leads to switching via 90° domain wedge nucleation for thicker films, due to the component of the electric field parallel to the film surface. At smaller thicknesses where the fringing of the electric field is less significant, the polarization switches directly by 180° rotations. The voltage required to switch the domain increases by decreasing the lateral size and at very small lateral sizes the coercive voltage becomes so large that it becomes virtually impossible to switch the domains, which is in agreement with other experimental and theoretical work suggesting a minimum critical width for ferroelectricity. In both geometries and both thicknesses investigated, the domains extend beyond the width of the electrode due to fringing of the electric field. It is believed that the additional energy cost of switching the regions beyond the width of the electrodes results in this increase in the coercive field.
9:00 PM - C9.12
Ab Initio Study of Ferroelectricity in Quantum-confined Nanostructures.
Ghanshyam Pilania 1 , Rampi Ramprasad 1
1 Department of Chemical, Materials and Biomolecular Engineering, University of Connecticut, Storrs, Connecticut, United States
Show AbstractFerroelectricity is a collective phenomena caused by a delicate balance between long-range coulombic and short-range repulsive forces. In nanostructures such as quantum dots and quantum wires, because of the lack of periodicity in 2 or more directions, this balance is altered with respect to bulk material. Despite a great amount of theoretical and practical work devoted to bulk and thin film ferroelectric (FE) materials, only few studies address the problem of ferroelectricity in such quantum-confined structures and therefore, very little is known concerning the evolution of ferroelectricity in such systems. Recent experimental work indicates that a lateral ferroelectric state is stable in barium titanate (BTO) nanowires with diameters as small as ~ 0.8 nm. Evidence for the presence of ferroelectricity along the axis of nanowires, and complex polarization patterns along the plane of nanodisks is also available through a limited number of theoretical and computational efforts. Nevertheless, a comprehensive understanding of the mechanism for the stabilization of novel polarization states, the size-, shape- and chemical environment-dependence of the various polarization states, and the fields above which (and temperatures below which) the polarizations can be switched from state to state are currently unavailable.In the present ab initio study, we have employed density functional theory to investigate the size dependence of ferroelectric properties of BTO quantum wires and quantum dots. In the case of quantum wires, the ferroelectric well depth, which is a measure of extent of the stability of the ferroelectric state over the paraelectric state, was calculated as a function of size. We find that the ferroelectric well depth corresponding to bulk BTO is recovered in quantum wires with diameters larger than 1 nm (corresponding to a cross section with 3x3 BTO units).. Analysis of the density of states (decomposed in terms of the contributing BTO units) indicates that the central BTO unit behaves bulk like, whereas the peripheral units result in defect states in the band gap (with density depending on whether they had BaO or TiO2 terminations). Complex polarization patterns (characterized in terms of relative Ti displacements) were also observed, and were strong functions of the surface termination of the nanostructures. For instance, in non-stoichimetric quantum wires with all surface facets terminated with TiO2, strong axial polarization was dominant. However, in BaO terminated quantum wires, polarization in the “shell” region is purely radial, while in the “core” region the polarization is purely axial. The BTO quantum dots that were studied displayed even more complex polarization patterns, reminiscent of the “vortex” patterns anticipated earlier based on effective hamiltonian calculations.
9:00 PM - C9.13
Ferroelectric-paraelectric Phase Transition Temperatures of an Array of Nanorods (nanocones) with a Gaussian Size Distribution.
Pavlo Bykov 2 , Gunnar Suchaneck 1 , Lubomir Jastrabik 2 , Igor Bykov 3
2 , Institute of Physics, CSAR, v.v.i., Prague Czechia, 1 Solid State Electronics Lab, TU Dresden, Dresden Germany, 3 , Institute for Problems of Materials Science, NASc of Ukraine, Kyiv Ukraine
Show AbstractMetamaterials are artificial composites which gain unusual properties from their inhomogeneous structure. They are promising for a variety of electromagnetic wave applications such as new types of modulators, band-pass filters, negative refractive index lenses, microwave couplers, antennas etc. Microwave frequency metamaterials are usually constructed as arrays of current-conducting elements which have suitable inductive and capacitive characteristics. Therefore, they have comparable high losses. On the other hand, dielectric metamaterials allow to expand the frequency range to THz and higher frequencies. Also, losses could be designed by an appropriate selection of the material. The basic structure of dielectric metamaterials is mostly an array of nanorods. However, for rod diameters in the nanometer range, size effects play an important role and the dielectric properties of the nanorod can not be extrapolated from bulk values.In this work, we investigate the behavior of the ferroelectric-paraelectric phase transition of an array of nanorods or nanocones made of ferroelectric material. The equation for the phase transition temperature was derived by a direct variational method from the Euler-Lagrange equation. In order to account for fabrication tolerances, a Gaussian distribution of rod sizes was assumed. Averaging of the phase transition temperature was performed by varying one of the geometric parameters (radius or high of the rod and height or cone angle, respectively). In result, the previously found enhancement of the transition temperature up to 2.5 time [1, 2] became blurred with an increasing size distribution. In order to conserve this effect, the distribution functions of geometric parameters of the cones and the wires must be extremely thin (for example, deviation of height in nanocones has to be less than ±2 nm). Averaging over both geometric parameters results in a mean value related to the most probable rod or cone.This work was supported by the German Research Foundation (DFG) as part of the Research Group FOR 520 and by the grant UKR 05/001 (International Bureau of the German Federal Ministry of Education and Research).[1] A.N. Morozovska, E.A. Eliseev, M.D. Glinchuk Phys. Rev. B. 2006, 73, 214106[2] P.I. Bykov, G. Suchaneck, M.A. Popov, G. Gerlach Ferroelectrics 2008 (in print)
9:00 PM - C9.14
Direct Nanoscale Measurement of the Domain Wall Hysteresis: Local Mapping of Lattice and Defect Pinning Sites.
Vasudeva Rao Aravind 1 , Samrat Choudhury 1 , Yulan Li 1 , Katyayini Seal 2 , Stephen Jesse 2 , Anna Morozovska 3 , Eugene Eliseev 4 , Sergei Kalinin 2 , Long-Qing Chen 1 , Venkatraman Gopalan 1
1 Materials Research Institute and Department of Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania, United States, 2 Materials Science and Technology Division and Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 3 V.Lashkarev Institute of Semiconductor Physics, National Academy of Science of Ukraine, pr. Nauki, Kiev, Ukraine, 4 Institute for Problems of Materials Science, National Academy of Science of Ukraine, Krjijanovskogo, Kiev, Ukraine
Show AbstractApplications of ferroelectric materials in data storage, piezoelectric, and FeRAM applications require understanding of domain wall motion mechanisms. Domain wall motion in ferroelectric materials is strongly affected by lattice, surface, and defect pinning effects. Since the seminal work of Miller and Weinreich [Physical Review 117, 1460 (1960)], it has been recognized that lateral domain wall motion velocity is controlled by the nucleation on single-unit cell thick domains, the thermodynamics of which controls wall motion [Y-H.Shin et al, Nature 449, 881 (2007) ]. In this work, we extend recently demonstrated approach [S.Jesse et al, Nature Mat. 7, 209 (2008)] for nucleation bias mapping in bulk materials to study domain nucleation and domain wall dynamics locally. Using scanning probe microscopy with ~10 nanometer resolution along with theoretical modeling, we demonstrate the role of 180o ferroelectric domain wall as an intrinsic defect that lowers coercive fields in its vicinity by an order of magnitude. The interaction of ferroelectric 180o domain wall with a strongly inhomogeneous electric field of biased scanning probe microscope tip is analyzed using continuous Landau-Ginzburg-Devonshire theory. Theoretical calculations predict that equilibrium shape of the initially flat domain wall boundary bends, attracts or repels from the probe apex, depending on the sign and value of the applied bias. The bending of the wall and its depolarization electric field facilitates tip induced domain nucleation. The experiments and theory and compared quantitatively, to show that lattice friction as well as lattice pinning play important role in the domain wall softening behavior. Ultimately, we demonstrate that the critical potential required for nucleation of a single Miller-Weinrech domain can be mapped in a spatially resolved fashion across the domain wall.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, and 2. We would like to acknowledge National Science Foundation for their financial support.
9:00 PM - C9.15
Local Polarization Dynamics and Bias-Induced Phase Transitions in Relaxor Ferroelectrics: Time-resolved Spectroscopy and Ergodic Gap Mapping.
Sergei Kalinin 1 , Stephen Jesse 1 , Oleg Ovchinnikov 1 , Maxim Nikiforov 1 , Anna Morozovska 2 , Alexei Bokov 3 , Zuo-Guang Ye 3
1 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 V. Lashkaryov Institute of Semiconductor Physics, National Academy of Science of Ukraine, Kiev Ukraine, 3 Department of Chemistry and 4D LABS, Simon Fraser University, Burnaby, British Columbia, Canada
Show AbstractThe unique electromechanical and dielectric properties of relaxor ferroelectrics made them the materials of choice for numerous applications, including SONAR, MEMS, ultrasonic imaging, and recently components of strain-modulated oxide electronic systems. The progress in these applications necessitates the understanding of relaxor behavior, including domain structures, field and temperature phase transitions, polarization relaxation dynamics, and effect on microstructure and spatial confinement on these properties. In this presentation, we delineate the applications of spatially resolved time- and voltage- spectroscopic imaging modes to address the relaxor behavior in PMN-PT solid solution crystals. For compositions close to the MPB, we observe the formation of classical ferroelectric domains with rough self-affine boundaries. In the ergodic phase (PMN and PMN-10PT), the formation of non-classical labyrinthine domain patterns characterized by a single characteristic length scale is observed. The persistence of these patterns well above Tc and the fact that they cannot be switched by tip bias suggest that the domains can be attributed to the static polarization component. Remarkably, these patters are not fractal. The ergodic phase is also characterized by the presence of relaxation polarization component that can be manipulated by the biased Piezoresponse Force Microscopy probe. Spatial variability of polarization relaxation dynamics in PMN-10PT is studied. Local relaxation attributed to the reorientation of polar nanoregions was found to follow stretched exponential dependence, with beta ~ 0.4, much larger than the macroscopic value determined from dielectric spectra (beta ~ 0.09). The spatial inhomogeneity of relaxation time distribution with the presence of 100-200 nm “fast” and “slow” regions is observed. The results are analyzed to map the Vogel-Fulcher temperatures on the nanoscale. The switching spectroscopy PFM is used to study local bias-induced phase transitions in relaxors. The applicability of this technique to map “ergodic gap” distribution on the surface is discussed. Research supported by the Division of Materials Science and Engineering, Basic Energy Sciences, U.S. Department of Energy at Oak Ridge National Laboratory, which is managed by UT-Battelle, LLC. The work at Simon Fraser University was supported by the U.S. Office of Naval Research.
9:00 PM - C9.16
The Order Parameter Coupling Effect on Ferroelectric Switching: Polarization Switching at a Single Ferroelastic Domain Wall in BiFeO3.
Nina Balke 1 , Katyayani Seal 2 , Stepehen Jesse 3 , Petro Maksymovych 2 3 , Mark Huijben 4 , Lane Martin 5 , Ying-Hao Chu 6 , Sergei Kalinin 2 3
1 Department of Materials Science and Engineering, University of California Berkeley, Berkeley, California, United States, 2 Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 3 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 4 Faculty of Science & Technology, University of Twente, Enschede Netherlands, 5 Department of Physics, University of California Berkeley, Berkeley, California, United States, 6 Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu Taiwan
Show AbstractFerroelectric thin films have been intensively studied over the last decades as material for Ferroelectric Random Access Memories (FeRAM). In many ferroelectric materials, the switching behavior is strongly mediated by the presence of secondary ferroelastic order parameter, and associated coupling to the built-in strain fields. These effects can be beneficial by enabling new types of device applications, and can also result in the formation of inactive ferroelastic twins. Here, we address the role of a single ferroelastic 71° domain wall in BiFeO3 on ferroelectric polarization switching using the combination of Piezoresponse Force Microscopy (PFM) and Switching Spectroscopy PFM. The standard vertical and lateral PFM illustrates the presence of ferorelastic walls, and confirms that the switching of the normal polarization component does not affect the in-plane component. The SSPFM allows collection of multiple hysteresis loops within the chosen region of the material. The examination of the observed maps illustrates that the ferroelastic wall does only slightly affect the out-of plane polarization component. At the same time, the 71° walls profoundly reduce the positive nucleation bias (PNB) from 4 V to 1 V, resulting in a clear structure in the PNB image. In comparison, the negative nucleation bias is not modified. These observations thus provide the direct information on the ferroelastic-mediated polarization switching. Research support of CNMS (user proposal number CNMS2008-R07) and financial support of the AvH foundation are greatly acknowledged.
9:00 PM - C9.17
All-optical Modulation of Ferroelectric Polarization Dynamics in PbTiO3.
Dan Daranciang 1 , Haidan Wen 3 , Aaron Lindenberg 2 3
1 Department of Chemistry, Stanford University, Stanford, California, United States, 3 PULSE Institute, Stanford Linear Accelerator Center, Menlo Park, California, United States, 2 Materials Science and Engineering, Stanford University, Stanford, California, United States
Show AbstractThe development of faster, higher density, non-volatile storage devices based on ferroelectric materials depends on an understanding of the fundamental limits governing how fast the polarization can be switched in an applied electric field. Previous work studying the fundamental speed limits for ferroelectric switching have utilized electrode structures and laser-driven photoconductive switches to couple one-hundred picosecond time-scale electrical pulses in order to induce switching dynamics. In this work we utilize near-half-cycle intense terahertz (THz) fields with pulse duration 300 femtoseconds to all-optically modulate the ferroelectric polarization in PbTiO3 in a contact-free geometry on femtosecond time-scales. The response of the ferroelectric is recorded by field-resolving the re-emitted THz field associated with the induced polarization modulation through electro-optic sampling. A nonlinear dependence of the reflected waveform on the incident THz electric field is observed.
9:00 PM - C9.18
Observation of a local dipole moment of Si atoms on Si(100) surfaces using Non-contact Scanning Nonlinear Dielectric Microscopy.
Nobuhiro Kin 1 , Yuhei Osa 1 , Yasuo Cho 1
1 Research Institute of Electrical Communication, Tohoku University, Sendai Japan
Show AbstractRecently, we have developed Non-Contact Scanning Nonlinear Dielectric Microscopy (NC-SNDM) with a height-control technique utilizing higher order nonlinear dielectric constant detection (ε(4) signal). We already succeeded in observing the typical Si(111) 7x7 atomic structure, which is well known in this field.Moreover, distribution of lowest order nonlinear dielectric signal ε(3) can be observed simultaneously. Then by our method, we made it possible to know a ferroelectric polarization distribution with an atomic resolution. [1]To confirm such performance of NC-SNDM, we attempted to know a local dipole moment of Si atoms on Si(100) cleaned surface under UHV conditions.As a result, we succeeded in observing a local electric dipole moment distribution of Si atoms on Si(100) 2x1 structure. At the weak applied negative voltage, a positive dipole moment is detected on the symmetric 2x1 dimer sites, whereas a negative dipole moment is observed at the interstitial sites. [1] Y. Cho and R. Hirose, Phys. Rev. Lett. 99, 186101 (2007).
9:00 PM - C9.19
Why are Garnets not Ferroelectric? -- A Theoretical Investigation of Y3Fe5O12.
Pio Baettig 1 , Tamio Oguchi 1
1 ADSM, Hiroshima University, Higashihiroshima Japan
Show AbstractResults of our study of the electronic, electric and magnetic properties of yttrium iron garnet, Y3Fe5O12 using first-principles calculations are presented. The cubic centrosymmetric structure and a tetragonally strained structure of Y3Fe5O12 are investigated. Frozen-phonon calculations are performed for both materials. We show, using symmetry arguments and by investigating the crystal structure, that pure garnets are unlikely candidates for being multiferroic materials despite their considerable magnetization at room temperature or above.
9:00 PM - C9.2
A Microscopic First-principles Understanding of Lead-free Piezoelectric Niobate Alloys.
Marco Fornari 1 2 , Nicola Marzari 2
1 Physics, Central Michigan University, Mt. Pleasant, Michigan, United States, 2 DMSE, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractNiobate alloys with perovskite-like structure exhibit a rich phenomenology which includes specific compositions with piezoelectric performances comparable with state of the art PZT materials. We have investigated (K,Na,A)(B,Nb)O3 composition with A=Li,Ag and B=Sb using first principles methodologies in order to unveil the microscopic mechanism and search for Pb-free piezoelectric materials. We found that the emergence of large electromechanical couplings rests on an electric field driven interplay between A-site offcenterings combined with strain effects and octahedral rotations. Our results point, especially, to: (a) large coupling between Li and Na distortions, (2) ion size effects related to Na-K substitutions, and (3) minor contributions associated with B-site alloying. The effect of an finite electrc field on the local structure and strain has been studied using electric-enthalpy density functional theory. We also discuss local structure and energy landscapes in order to provide first principles based strategies to distiguish morphotropic phase boundary and polymorphic phase transitions.
9:00 PM - C9.20
Linear and Non-Linear Electrostrctive Coupling in Ferroelectrics: Effect on Properties and First Principles Calculations.
Alexander Tagantsev 1 , Guido Gerra 1 , Nava Setter 1
1 Ceramics Laboratory, IMX, Swiss Federal Institute of Technology (EPFL), Lausanne Switzerland
Show AbstractThe electrostrictive coupling is an effect which has a profound impact on the properties of ferroelectric systems. This coupling, for example, controls the morphic piezoelectric effect in the ferroelectric phase. It also governs the misfit-strain-induced increase of the ferroelectric phase transition temperature in thin films [1]. Within the Landau theory, this effect is introduced via the qijkluijPkPl term in the free energy expansion (where uij and Pk are the components of the strain tensor and polarization). For ferroelectrics with a centrosymmetric paraelectric phase, this terms is that of the lowest order among those describing the electromechanical coupling. The next-order terms are RijklstuijPkPlPsPt and mstijklustuijPkPl. The couplings associated with these terms can be classified as non-linear electrostictive ones. These terms have been customarily neglected in phenomenological treatments of ferroelectrics assuming that there are no qualitative effects behind these couplings and that the relevant quantitative effects are weak. However, it has been recently realized that this may not always be the case. It has been shown that the RijklstuijPkPlPsPt coupling may substantially (qualitatively!) affect the phase diagrams of ferroelectric thin films [2], whereas the mstijklustuijPkPl. term may be important for the description of the performance of tunable Thin Film Bulk Acoustic wave Resonator (TFBAR)[3]. In this paper we discuss the role of non-linear electrostictive coupling in ferroelectrics. Another issue addressed in this paper is Density Functional Theory (DFT) calculations of the qijkl and mstijkl tensors. First, we present the results of our calculations for m/q ratios for BaTiO3 and SrTiO3. Second, we will discuss the problems involved in the ab-initio calculation of the linear electrostrictive tensor qijkl. Here the point is that the DFT-calculated values of the components of this tensor presently available in the literature, strongly disagree with those experimentally measured.[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]A. K. Tagantsev, N. A. Pertsev, P. Muralt, and N. Setter, Phys. Rev.B 65, 012104 (2002).[3]A. Noeth, T. Yamada, V. O. Sherman, P. Muralt, A. K. Tagantsev, and N. Setter, Journal of Applied Physics 102 (2007).
9:00 PM - C9.21
A Finite Temperature First-Principles Model to Understand Magnetic and Lattice Fluctuations in Multiferroic Materials.
Yi Wang 1 , Shun-Li Shang 1 , Hui Zhang 1 , Zi-Kui Liu 1 , Long-Qing Chen 1 , Craig Fennie 2
1 Materials Science & Engineering, Penn State, University Park, Pennsylvania, United States, 2 School of Applied and Engineering Physics, Cornell University, , Ithaca, New York, United States
Show AbstractIn the past decades, steady increases in both computer power and the efficiency of computational methods have made accurate first-principles calculations of material properties at finite temperature a realistic goal. The current frontier is how to extend the first-principles approach when the role of non-spatial internal degrees of freedom becomes important. One example of much current interest is the interplay between magnetic and lattice fluctuations at finite temperature. Solution of this enigma can reveal the microscopic origin of the novel properties of many materials. Hereby we establish a quantitative thermodynamic relationship between magnetic and lattice fluctuations with a precise first-principles formulation of the Helmholtz free energy. This is accomplished by considering the finite temperature mixing of a variety of electronic states, each distinguished by different spin distributions/configurations in the lattice. The present prototypes are SrRuO3 and EuTiO3 for which we have made attempts to understand the relationships among magnetism, polarization, temperature, volume, strain, and the free energy.
9:00 PM - C9.22
The Variation of Local Strain-field Across the Interface in a PZT/Ni0.8Zn0.2Fe2O4/PZT Tri-layered Structure as Studied using in Situ X-ray Microdiffraction.
Suk-Jin Ahn 1 , Chung W Bark 1 , Jung H Park 1 , Eun H Na 1 , Yang M Koo 1 , Hyun M Jang 1
1 , Pohang University of Science and Technology (POSTECH), Pohang Korea (the Republic of)
Show AbstractThere have been a continual interest in the study of magnetoelectric (ME) materials for many years due to their potential applications for new functional oxides such as electric-field-controlled ferromagnetic resonance devices, actuators, transducers, and storage devices.As the single-phase ME materials turned out to be rare at room temperature, the importance of the strain-mediated ME coupling in a two-phase structure with alternatively stacking magnetostrictive and piezoelectric layers has been increasingly recognized. Previous researches have revealed that multilayered structures consisting of piezoelectric and magnetostrictive layers can have larger ME coupling effects than those of bulk composites at room temperature. Since the ME coupling in a multilayered structure is believed to occur dominantly at the interfacial region between constituting ferroelectric and ferromagnetic layers, it is important to quantify the spatial distribution of the local strain-field across the interface. However, no direct measurement of the local strain has been performed prior to the present study. In this study, we adopted an in-situ scanning probe method, called x-ray microdiffraction, to quantitatively monitor the variation of the local strain-field across the interface. By adopting this emerging technique, we were able to estimate the variation of the local strain-field in a Pb(Zr0.52Ti0.48)O3/Ni0.8Zn0.2Fe2O4/Pb(Zr0.52Ti0.48)O3 tri-layered structure under an applied electric field. We observed that the electric-field-induced strain decreased rapidly with the distance from the interface.
9:00 PM - C9.23
Magnetic Color Symmetry of Lattice Rotations in a Non-magnetic Material.
Sava Denev 1 , A. Kumar 1 , M. Biegalski 1 , H. Jang 2 , C. Folkman 2 , A. Vasudevarao 1 , Y. Han 3 , I. Reaney 3 , S. Trolier-McKinstry 1 , C. Eom 2 , D. Schlom 1 , V. 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 Department of Engineering Materials, The University of Sheffield, Sheffield United Kingdom
Show AbstractOxygen octahedral rotations are the most common phase transitions in perovskite crystal structures. We show that the color symmetry of such pure elastic distortions is isomorphic to magnetic point groups, which allows their probing through distinguishing polar versus magnetic symmetry.[1] We demonstrate this isomorphism using nonlinear optical probing of the octahedral rotational transition in a compressively strained SrTiO3 thin film that exhibits ferroelectric (4mm) and antiferrodistortive (4'mm') phases evolving through independent phase transitions. The approach has broader applicability for probing materials with lattice rotations that can be mapped to color groups.
[1] Phys. Rev. Lett. 100, 257601 (2008)
9:00 PM - C9.24
Strain Relaxation in Epitaxial SmScO3 and PrScO3 Films Grown on (110) NdGaO3 Substrates.
Christopher Nelson 1 , Xiaoqing Pan 1 , Chad Folkman 2 , Chang-Beom Eom 2
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
Show AbstractPrScO3 and SmScO3 films with a thickness of 200 nm were grown by pulsed laser deposition on (110) NdGaO3 substrates. Both x-ray diffraction and transmission electron microscopy (TEM) show that the epitaxial strains are nearly fully relaxed in these films. Cross-sectional TEM analysis reveals that both films are single domain and contain threading dislocations originating from the film/substrate interface resulting from the strain relaxation. This relaxation occurs by the formation of a psuedocubic a<100> periodic dislocation array at a slight stand-off from the interface. Some dislocations are disassociated into two ½a<101> partials. The stand-off distance is approximately 1 nm for PrScO3 and about 7nm for SmScO3, values much larger than we would expect from theoretical calculations. The difference in interface structure between the SmScO3/NdGaO3 and PrScO3/NdGaO3 samples as well as their departure from conventional equilibrium stand-off distance predictions will be discussed.
9:00 PM - C9.25
Structure and Transport Properties of the Interface Between Epitaxial KTaO3 Thin Films on SrTiO3 Substrates.
Nikolina Ljustina 1 , Johan Borjesson 1 , Alexey Kalabukhov 2 , Dag Winkler 2 , Eva Olsson 1
1 Microscopy and Microanalysis, Chalmers Univ. of Tech., Göteborg Sweden, 2 Microtechnology and Nanoscience, Chalmers Univ. of Tech., Göteborg Sweden
Show Abstract9:00 PM - C9.26
Octahedral Tilt Transitions in Perovskite Thin Films.
Daniel Tinberg 1 , Susan Trolier-McKinstry 1 , Yisong Han 2 , Ian Reaney 2 , Stephen Streiffer 3 , Dillon Fong 4
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 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, United States, 4 Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractIn bulk ferroelectric materials with the perovskite structure, the transition from an untilted oxygen octahedral framework to a tilted one 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. The presence of octahedral tilting for a 1 micron thick PZT 70/30 film was confirmed. 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. 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/m2 for PZT 80/20 films, increasing to -9.1 C/m2 for PZT 60/40 films. Both electrical and structural measurements characterizing the tilt transition will be reported. Ultimately, the possibility of stabilizing ferroelectric phases which are not simultaneously tilted, may widen the range of films which have high piezoelectric coefficients at morphotropic phase boundaries. It is the goal of this project to determine under what conditions this may occur.
9:00 PM - C9.27
Reflection High-energy Electron Diffraction Study of K(Ta,Nb)O3 Thin-film Epitaxy.
Joseph Cianfrone 1 , Mathew Ivill 1 , Charlee Callender 1 , Lynn Boatner 2 , David Norton 1
1 Materials Science and Engr, University of Florida, Gainesville, Florida, United States, 2 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractAn interesting ferroelectric material system for understanding and manipulating ferroelectric properties is K(Nb,Ta)O3. It is similar to (Sr,Ba)TiO3 in that the solid solution possesses a continuous transition from a paraelectric to a ferroelectric material. KTaO3 is cubic and paraelectric at all temperatures. KNbO3, in contrast, exhibits a first-order ferroelectric phase transition accompanied by a change from the cubic to the tetragonal structure at 701 K. As a solid solution, K(Ta,Nb)O3 exhibits a continuous Curie temperature that varies according to the formula Tc (K)= 676x + 32 (x>0.047). The pseudo-cubic lattice parameter of KNbO3 (ap= 4.014 Å, T=25 °C) differs from that for KTaO3 by only 0.6 %. One significant challenge in the growth of epitaxial K(Ta,Nb)O3 is the high vapor pressure of potassium. To prevent the loss the potassium during growth and to maintain stoichiometry in the films, an overpressure of K must be provided. In pulsed-laser deposition, this is achieved either by growing from a K-rich target or sequentially ablating from two targets, one KNO3 and the other K(Ta,Nb)O3. We have examined the K(Ta,Nb)O3 thin film growth process using reflection high-energy electron diffraction (RHEED). Experiments include the growth of K(Ta,Nb)O3 on near-perfect lattice-matched single crystal (001) KTaO3 as well as SrTiO3. Changes in diffraction patterns and intensity oscillations in RHEED are observed with variations in growth temperature, background pressure, and in the K(Ta,Nb)O3 - KNO3 target ablation sequencing. Correlations between 3-D island, 2-D layer-by-layer, and/or step flow growth and results from RHEED will be discussed. Atomic force microscopy is used to characterize the surface morphology for films grown under these conditions. Characterization includes AFM, TEM, X-ray diffraction, and dielectric measurements.
9:00 PM - C9.28
Pyroelectric Quasi-Amorphous Thin Films as Templates for Controlling Crystal Nucleation.
David Ehre 1 , Etay Lavert-Ofir 1 , Isabelle Weissbuch 1 , Meir Lahav 1 , Igor Lubomirsky 1
1 Materials and Interfaces, Weizmann Institute of Science, Rehovot Israel
Show AbstractWe present irrefutable experimental evidence that the charge developing at the surface of pyroelectrics can be used to control crystal nucleation. Although an externally-applied electric field is known to affect crystal nucleation, the role of surface charge remains unclear because it cannot be separated from the influence of surface morphology and/or epitaxial effects. To separate these effects, we compared non-polar amorphous thin films of SrTiO3 with polar quasi-amorphous films that were prepared from these amorphous films. Transformation of the amorphous to the quasi-amorphous films does not cause change of composition or surface roughness. Therefore, amorphous/quasi-amorphous film pair is a nearly perfect system to separate the influence of electric field from that of epitaxy effects. Furthermore, given that the charge is created at the surface of pyroelectric materials only in response to temperature variation, crystallization under isothermal conditions is not affected by the electric field. This provides two additional points of reference: (1) nucleation at the surface of the quasi-amorphous films upon varying temperature and under isothermal conditions should yield different results; (2) amorphous and quasi-amorphous films under isothermal conditions must be indistinguishable.We provide two experimental examples: the crystallization of the metastable polymorph of β-glycine from aqueous solutions and the catalysis of freezing of supercooled water. For the case of nucleation of glycine we have used both “zero field” points of reference: amorphous vs. quasi-amorphous films and quasi-amorphous films upon cooling vs. quasi-amorphous films under isothermal conditions. In both cases, the β-polymorph appears only on the surface which develops the surface charge (the quasi-amorphous films upon cooling). This fact unambiguously points out that it the surface charge that causes formation of the metastable β-polymorph.Freezing of the water drops on the quasi-amorphous thin films occurred at -4 ±0.3 °C, whereas at the surface of the amorphous films, the drops froze at -12 ±0.3 °C. Due to the very large enthalpy of crystallization of water (6 kJ/mol), the difference of 8 degrees in the freezing point must be viewed as extremely large.The role of the charging of pyroelectric materials should have important implications in various fields of science spanning from the applied problems of controlling crystal polymorphism to the fundamental questions of bio-mineralization. Therefore, one can expect that our findings will open a new field for the application of the pyroelectric materials.
9:00 PM - C9.29
Stability of the Polar Phase in Ultra-thin BaTiO3 Films Exposed to H2O.
Junsoo Shin 1 2 , V. Nascimento 1 2 , E. Plummer 1 3 , S. Kalinin 2 3 , A. Baddorf, 3
1 Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee, United States, 2 Materials Science and Technology Division, Oak Ridge National Lab., Oak Ridge, Tennessee, United States, 3 Center for Nanophase Materials Sciences Division, Oak Ridge National Lab., Oak Ridge, Tennessee, United States
Show AbstractBaTiO3 (BTO) thin films have been widely studied for applications in ferroelectric random-access memories and high-density capacitors because of their high dielectric constant and low leakage current. However, the role of charge compensation on ferroelectric surfaces and its interplay with the ferroelectric size effect has been debated for over 50 years. The contribution of surface charge scales inversely with thickness and strongly affects the stability of polarization in ultra-thin ferroelectric films. Recently, we have experimentally addressed polar ordering in ultra-thin (4 and 10 ML) BTO films grown on SrRuO3 electrodes by Pulsed Laser Deposition (PLD). Those ultrathin BTO films with BaO termination demonstrated a single-domain vertically polarized upward, determined by in-situ low energy electron diffraction intensity vs. voltage (LEED-IV) analysis. We report here the stability of the polar phase in ultra-thin BTO films and characterized in an ultrahigh vacuum environment after the surface was exposed to H2O. A 10 ML BTO film was grown by PLD and subsequently exposed to 1.8x104, 6x104, and 3.6x105 L H2O vapor and characterized using LEED. The exposure of the ferroelectric films to H2O vapor affects the stability of the vertically polarized structure in sub-surface layers due to surface compensation. LEED intensities indicate a significant change in surface structure, which nevertheless retain the (1x1) P4mm symmetry. LEED-IV analysis suggests that the polarity of the film is reversed by water exposure, and the best structural model indicates significant oxygen vacancy density in the top BaO layer. We interpret these observations as a formation of a diffuse solvated water layer that contains counterions to maintain electroneutrality, but due to its diffuseness does not contribute to LEED data. Research was sponsored by the Division of Materials Science and Engineering and the Center for Nanophase Materials Sciences at Oak Ridge National Laboratory, for the U. S. Department of Energy.
9:00 PM - C9.3
Giant Piezoelectric Response in Thin-film PbTiO3 from First-principles.
Yoshitaka Uratani 1 , Tatsuya Shishidou 1 , Tamio Oguchi 1
1 quantum matter, Hiroshima University ADSM, Hiroshima Japan
Show AbstractPiezoelectric, ferroelectric and relaxor materials have fundamental interests and their various applications are crucial for electronic devices. Particularly, an application to piezoelectric sensor is extremely important for electro-mechanical transducers. PbTiO3 is one of the simplest ferroelectric oxides and its related compound PbZn1/3Nb2/3O3- PbTiO3(PZN-PT) have an ultra-high piezoelectric coefficient for morphotropic phase boundary (MPB). One of the noteworthy first-principles approaches to MPB has been recently reported [1]. It has been found that isotropic pressure induces anomalous phase transitions and giant enhancement of piezoelectricity even in a single phase PbTiO3, in relation to MPB. In an application point of view, however, the piezoelectric mechanism in ferroelectric thin-films should be investigated. In this paper, we report ferroelectric and piezoelectric properties of PbTiO3 in a thin-film form calculated from first principles. Especially, its epitaxial strain dependence and giant piezoelectric response are discussed. In recent progress of the thin-film synthesis techniques, misfit-strain control becomes now realistic in contrast to pressure-induced response. So, our study may contribute to a realistic materials design approach. We have performed first-principles calculations based on the density functional theory within the local density approximation (LDA). We have used the all-electron full-potential-linear-augmented-plane-wave (FLAPW) method in a scalar-relativistic scheme. Electronic polarization, Born effective charges and piezoelectric coefficients are determined by using the Berry phase theory. First, we show results of the in-plane lattice constant dependence of electric polarization and the lattice constant ratio c/a. All the atomic positions and the c/a ratio are fully optimized within P4mm space group for each in-plane lattice constant a. Calculated electric polarization and optimized c/a ratio are decreased with increasing a, being comparable with the previous report [2]. It is found that the change in the electric polarization is mostly due to that in the ionic displacements associated with the c/a ratio. Next, LDA calculated results of the piezoelectric coefficients e31 , e31 and e15 are shown. In e33 and e31, maxima are found near 3.90Å. Since our fully optimized bulk tetragonal lattice constants are a=3.875Å with c/a = 1.039, the maxima appear near the optimized lattice. In e15, a divergent feature is seen near the optimized lattice. This can be understood by strain induced phase boundary in a thin film. Such giant and enhanced piezoelectric coefficients may possibly be interpreted within a variation of potential surface near the phase boundary.[1] Z. Wu and R. E. Cohen, Phys. Rev. Lett. 95, 037601 (2005).[2] Ho Nyung Lee, et al., Phys. Rev. Lett. 98, 217602 (2007).
9:00 PM - C9.30
Photo-Devices Based on BiFeO3 Thin Films – Understanding Light Interactions with Ferroelectricity.
Lane Martin 1 , Thomas Conry 2 , Sourav Basu 2 , R. Ramesh 1 2 3
1 Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 2 Materials Science and Engineering, University of California, Berkeley, Berkeley, California, United States, 3 Physics, University of California, Berkeley, Berkeley, California, United States
Show AbstractOver the last few years, multiferroic materials such as BiFeO3 (BFO) have been the focus of much research aimed at utilizing the ferroelectric and magnetic properties of such materials. Unlike classic ferroelectrics like PbTiO3 and BaTiO3, recent evidence suggests that some multiferroic materials like BFO, with a direct band gap of 2.6 eV, could likewise be interesting for optical devices – including light activated memories, photoamplifiers, photoconductors, photovoltaics, and more. In this work we report the study of light interactions with BFO. Absorption studies have shown that fully epitaxial thin films of BFO exhibit excitations at 3.2 and 4.5 eV that are likely charge transfer in character and the primary band gap has been measured to be ~2.6 eV, consistent with theoretical predictions. We also report a study of the effect of photo-excitation of carriers on the ferroelectric polarization in this material. Preliminary evidence suggests that exposure of BFO to strong visible light can result in ferroelectric switching even at zero applied field. The true physics underlying the evolution of polarization under illumination is not fully understood; we are exploring possible explanations for this effect. Additionally, we will present the observation of large photoconductivities in BFO thin films that can be tuned by controlling the defect chemistry of the multiferroic phase. Significant differences in the light and dark current-voltage (IV) characteristics are found in fully oxidized films of BFO – current densities of 458 mA/cm2 and 720 mA/cm2 were measured at an applied voltage of 2V for light and dark respectively. Finally, with the ever increasing need for alternative energy sources as a backdrop, the search for new candidate photovoltaic materials is underway. Oxide materials – unparalleled in stability, abundance, and versatility – offer an exciting direction for further study in this capacity. We have measured photovoltaic effects in BFO thin films and achieved efficiencies near ~1% with very large VOC (~0.8-0.9V). The large polarization of BFO (PS ~ 100 μC/cm2) – which translates into an electric field of over 109 V/m – could be used in place of a classic pn-junction to separate charge carriers in a photovoltaic device. In this work we will discuss the role that ferroelectricity plays in controlling the photovoltaic effect in BFO. This work is supported by the Department of Energy.
9:00 PM - C9.31
Organic Non-volatile Memories from Ferroelectric Phase Separated Blends.
Kamal Asadi 1 , Dago M. de Leeuw 1 2 , Bert de Boer 1 , Paul W. M. Blom 1
1 , University of Groningen, Groningen Netherlands, 2 , Philips Research Laboratories, Eindhoven Netherlands
Show AbstractNew non-volatile memories are being investigated in order to keep up with the organic electronics road map. Ferroelectric polarisation is an attractive physical property as the mechanism for non-volatile switching, since the two polarisations can be used as two binary levels. However, in ferroelectric capacitors the read-out of the polarisation charge is destructive. The functionality of the targeted memory should be based on resistive switching. In inorganic ferroelectrics conductivity and ferroelectricity cannot be tuned independently. The challenge is to develop a storage medium in which the favourable properties of ferroelectrics such as bistability and non-volatility can be combined with the beneficial properties provided by semiconductors such as conductivity and rectification. In this contribution we present an integrated solution by blending semiconducting and ferroelectric polymers into phase separated networks. The polarisation field of the ferroelectric modulates the injection barrier at the semiconductor–metal contact. The combination of ferroelectric bistability with (semi)conductivity and rectification allows for solution-processed non-volatile memory arrays with a simple cross-bar architecture that can be read-out non-destructively[1]. The concept of an electrically tunable injection barrier as presented here is general and can be applied to other electronic devices. A non-volatile, yet reversible switchable Schottky diode with relatively fast programming time of shorter than 100 microseconds, long information retention time of longer than 10 days, and high programming cycle endurance of more than 1000 (read, write, read and erase cycles) with non-destructive read-out is demonstrated. The resistivity of this diode is modulated between non-volatile high- and low-resistance states (Boolean 0 and 1) by applying a switching pulse, whereas lower voltages allow for reading of the information non-destructively.[1] K. Asadi, D. M. de Leeuw, B. de Boer, P. W. M. Blom, Nature Materials 7, 2008, 547-550.
9:00 PM - C9.32
Fatigue Property of Shape Memory Piezoelectric Actuator by Continuous Cycling of Polarization Switching.
Yoichi Kadota 1 , Hiroshi Hosaka 1 , Takeshi Morita 1
1 Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa Japan
Show Abstract Ferroelectric materials are widely utilized for various device applications. For example, using their remnant polarization switching, high density nonvolatile media were developed. Besides, as piezoelectric materials, they are used for actuator application, such as precision positioning stages, actuator for ink jet printing system, ultrasonic motors, micro-electro-mechanical systems and etc. These applications utilize quite different property of ferroelectric materials. For memory application, polarization switching is utilized. On the other hand, for actuator application, the polarization switching is never used. However, a shape memory piezoelectric actuator that utilizes polarization switching for actuator application had been proposed by using the asymmetricity of ferroelectric properties of the actuator caused by the imprint electrical field [Ref. 1]. About the conventional ferroelectrics, their multifunctional properties, such as piezoelectric strain, permittivity, reflective index and etc. have a symmetric hysteresis about electrical field axis with bipolar loading except for polarization. Thus, only its polarization has memory effect. However, when the electrical imprint field is induced, the polarization hysteresis of the ferroelectric material shifts to the electrical field axis. At this time, not only its polarization hysteresis but also other ferroelectric properties shift to the electrical field axis and become asymmetric. Then, they become to have two stable values according to its polarization direction at the point of 0 electrical field; that means memory effect can be generated. Utilizing this principle for actuation, the shape memory piezoelectric actuator is realized. In this study, the fatigue property of the shape memory piezoelectric actuator was investigated by continuous switching of its polarization. The shape memory piezoelectric actuator was fabricated by using commercially available soft-type PZT unimorph actuator (Nihon Ceratec Co., Ltd., LPD3713X). The electrical imprint field was induced by applying high DC field of 3.5 kV/mm in high temperature of 150°C for several hours. Fatigue test was carried out by applying continuous pulses plus and minus one after the other. The change of the amount of shape memory gap was measured with some conditions of the time for inducing the imprint or the amplitude and the pulse width of the driving voltages. The fatigue of the shape memory was revealed that at first it changes drastically and after that it becomes stable state (over about 104 cycling). At least, we confirmed the shape memory effect continues over 105 cycling. The polarization hysteresis and displacement hysteresis of the actuator was measured before the fatigue and after. This measurement showed slight decrease of the electrical imprint field of the actuator after fatigue.Ref. 1: “Shape memory piezoelectric actuator”, Takeshi Morita, Yoichi Kadota, Hiroshi Hosaka, Appl. Phys. Lett., 90, 082909, (2007)
9:00 PM - C9.33
Controlled Ag Nanopattern Formation through UV Wavelength Dependent Photochemical Interactions on PPLN.
Yang Sun 1 , Robert Nemanich 1
1 Physics, Arizona State University, Tempe, Arizona, United States
Show AbstractThis study establishes that ferroelectric nanolithography is dependent on the excitation wavelength and that the process can be controlled through optimization of the wavelength dependent photochemical surface interactions. Periodically poled lithium niobate (PPLN) is used as a template for “nanolithography” of metallic nanoparticles and nanowires through a photochemical process. Prior research has established that above band gap UV emission is necessary to initiate the deposition process. Depending on the nature of the surface screening, the deposition will occur predominantly on the positive domains (internal screening) or at the domain boundaries (external screening). This research employs PPLN, which exhibits external screening, and it is shown that the location and rate of Ag nanostructure deposition is dependent on the wavelength of the UV excitation. The selective deposition is explained by a combined theory of band-bending, the mechanism of polarization surface charge screening, and the absorption depth of the UV light. As an application example, the Ag nanopatterns are employed for spatially specific surface enhanced Raman spectroscopy (SERS). Other applications include use as a photocatalyzer for direct assembly of dissimilar molecules into functional nanostructures and devices. Research supported by the NSF NIRT Grant No 0403871.
9:00 PM - C9.34
Laser Beam Shaping using Electro-optic Devices Based on Ferroelectric Domain Engineering.
Mahesh Krishnamurthi 1 , Peng Li 2 , Zhiwen Liu 2 , Venkatraman Gopalan 1
1 Material Science and Engineering, Penn State University, State College, Pennsylvania, United States, 2 Electrical Engineering, Penn State University, State College, Pennsylvania, United States
Show Abstract9:00 PM - C9.35
Interfacial Engineering and Magnetoelectric Coupling Properties in Pb(Zr0.53 Ti0.47)O3/CoFe2O4 Multiferroic Epitaxial Multilayers.
Jinxing Zhang 1
1 Applied Physics, The Hong Kong Polytechnic University, Hong Kong China
Show AbstractMagnetoelectric (ME) nanocomposite materials have been attracting a great deal of attention due to its potential applications in many multifunctional devices [1, 2] which may not be realized in their bulk counterparts. The observation of ME coupling in the self-assembled multiferroic BaTiO3 (BTO) / CoFe2O4 (CFO) nanostructures [3] motivated a broad range of research in multiferroic nanocomposites from the aspects of experimental characterization [4,5] and theoretical calculation [6]. In this work, epitaxial Pb(Zr0.53Ti0.47)O3 (PZT) / CoFe2O4 (CFO) multilayered nanocomposite thin films with up to 11 alternative layers are grown on Nb doped SrTiO3 (Nb: STO) substrates by pulsed-laser deposition (PLD). X-ray diffraction and high resolution transmission electron microscopy studies of the films reveal the good epitaxial relationship between the PZT and CFO layers. Strong ferromagnetic and ferroelectric responses are simultaneously observed at room temperature. The lattice mismatch between perovskite and spinel layers are responsible for the residual strain in each phase, indicating the interfacial coupling. The interfacial coupling-modulated dielectric behavior, polarization and magnetic properties are observed and analyzed systematically. Stress-induced polarization and dielectric behavior in the multiferroic nanocomposite are in line with our theoretical prediction,; while space charges between the interfaces do not increase with the number of layer according to our calculation and experimental data. The ferroelectric and ferromagnetic behaviors in PZT/CFO epitaxial multilayer nanocomposite can be modulated by the residual strain from the neighbor layers of each other, influenced by the coupling effect in PZT/CFO interfaces. With these results, we conclude that multiferroic properties and their coupling effect can be tuned by the “strain engineering” in this multiferroic superlattice.Reference1, N. A. Spaldin and M. Fiebig, Science 309, 391 (2005).2, J. F. Scott, Science 315, 954 (2007)3, H. Zheng, J. Wang, S. E. Lofland, Z. Ma, L. Mohaddes-Ardabili, T. Zhao,L. Salamanca-Riba, S. R. Shinde, S. B. Ogale, F. Bai, D. Viehland, Y. Jia,D. G. Schlomm, M. Wuttig, A. Roytburd, and R. Ramesh, Science 303, 661 (2004).4, Igor Levin, Jianhua Li, Julia Slutsker and Alexander L. Royburd, Adv. Mater. 18, 2044-2047 (2006)5, Q. Zhan, R. Yu, S. P. Crane, H. Zheng, C. Kisielowski and R. Ramesh, Appl. Phys. Lett. 89, 172902 (2006)6. Ce-Wen Nan, Gang Liu, Yuanhua Lin and Haydn Chen, Phys. Rev. Lett. 94, 197203 (2005)
9:00 PM - C9.4
Ab Initio Studies on Linear and Nonlinear Optical Properties of CsGeCl3 and CsGeBr3 Crystals.
Li-Chuan Tang 1 2 , Yia-Chung Chang 2 3 , Chen-Shiung Chang 1 , Jung-Yau Huang 1
1 Photonics, Institute of Electro-Optical Engineering, IEO, Hsinchu Taiwan, 2 The Research Center for Applied Sciences (RCAS), Academia Sinica, Taipei Taiwan, 3 Physics, UIUC, Urbana-Champaign, Illinois, United States
Show Abstract9:00 PM - C9.5
Ferroelectric Properties of Co-axial Noble-metal/oxide core/shell Perovskite Nanowires.
Stephen Nonnenmann 1 , Eric Gallo 1 , Rahul Joseph 1 , Michael Coster 1 , Oren Leaffer 1 , Bahram Nabet 1 , Jonathan Spanier 1
1 Materials Science & Engineering, Drexel University, Philadelphia, Pennsylvania, United States
Show Abstract9:00 PM - C9.6
Modulations of the Spin Structure and the Orbital Hybridization in Epitaxially Constrained BiFeO3 Thin Films.
Sangwoo Ryu 1 , Jae-Young Kim 2 3 , Hyun M. Jang 1 3
1 Dept. of Materials Science and Engineering, POSTECH, Pohang, Gyung-buk, Korea (the Republic of), 2 Pohang Accelerator Laboratory (PAL), POSTECH, Pohang, Gyung-buk, Korea (the Republic of), 3 Dept. of Physics, POSTECH, Pohang, Gyung-buk, Korea (the Republic of)
Show AbstractMultiferroics are an interesting group of materials that possess simultaneous ferroelectric, ferroelastic and magnetic orderings. Among them, BiFeO3 with rhombohedral R3c crystal symmetry is known to be the only single-phase material that exhibits multiferroic properties at room temperature. Although it is still controversial, we obtained experimentally that the epitaxial constraints have enhanced the ferroelectric and ferromagnetic properties. To understand this strain-induced enhancement of the multiferroic properties, we have adopted polarization dependent x-ray absorption spectroscopy. We observed that the linear dichroism was strengthened with increasing misfit strain at Fe L2,3-edges, which suggests the rotation of the antiferromagnetic spin axis. We further observed that the dichroism at O K-edge had the same dependence on the misfit strain. In addition to these, the peak splitting around 530eV became distinct as the misfit strain decreased. These indicate some changes in the orbital-selective unoccupied electronic structure and the Fe 3d – O 2p orbital hybridization. From these studies, we suggest that the enhancement of the magnetization is caused by the modulation of the spin structure which originates from the epitaxial misfit strain between the BiFeO3 thin film and the substrate.
9:00 PM - C9.7
Local Implanted Mediated Strain and Anomalous Local Etch Rate in Deep He Ion-Implanted LiNbO3.
Avishai Ofan 1 , Ophir Gaathon 1 , Richard Osgood 1 , Lakshmanan Vanamurthy 2 , Hassaram Bakhru 2 , Kenneth Evans-Lutterodt 3
1 Center for Integrated Science and Technology, Columbia University, New York, New York, United States, 2 College of Nanoscale Science and Engineering, State University of New York at Albany, Albany, New York, United States, 3 National Synchrotron Light Source, Brookhaven National Laboratory, Upton, New York, United States
Show AbstractImplantation of high energy He ions is known to lead to rapid, high-selective etching in complex oxides such as ferroelectrics. Its applications include ion slicing or exfoliation of thin single-crystal layers and patterning. A remarkable feature of many of these applications is the extreme selectivity of the etch process. This talk will focus on experiments to understand this enhancement and its relation to He-implant lattice strain -for the case of implanted LiNbO3 crystals. Our experiments use measurements via optical microscopy “movies”, atomic force microscopy, Rutherford backscattering/channeling, and synchrotron X-ray-diffraction microprobing. In the process, we directly follow the etch front in the submicrometer-scale implant region and directly image the strain using X-ray microprobe. Our study of the effect of the thermal treatment of the 3.8 MeV implanted crystal, typically ~5x1016 cm-2, on the wet etching rate shows that there is a small range of temperatures, over which high etch rates are enabled by the post implantation annealing; samples that have been annealed at too low or too high a temperature does not undergo measurable etching. Our microscopy work shows that heavy implantation of high-energy He+ ions in LiNbO3 can be seen to induce a sub-micron crystal-domains structure in the heavy implantation region, which is buried ~10μm below the surface with a straggle of ~400nm for the conditions mentioned above. In addition in a dilute acid bath, the etchant has been found to be transported through the implant region at a velocity of >5μm/min but is confined to ~0.5μm-wide buried channels resulting in very inefficient etching. However, our probes showed that after very mild thermal processing the density of the domains were fundamentally altered, i.e. after annealing the samples to the temperature required for etching, i.e. 250oC, additional domain structure appears within the implantation region. This additional structure eliminates the channels mentioned above and as a result, a very fast etch rate of the order of a few μm/min is achieved. Finally and remarkably further annealing of a pre-annealed sample to a higher temperature removes all evidence of the domains; this annealing also disables the etching process. Note that RBS/channeling has also been used to correlate thermal processing in the implanted sample and the ion-induced structural changes in the samples by post annealing temperature. Finally, measurements of the crystal strain using a ~10keV microprobe X-ray beam at Brookhaven National Laboratory show intensity variation in the X-ray, which correlates with the crystal domains; this behavior is attributed to the formation of local tilted regions. The X-ray results suggest that the microstructures are dislocation pileups as a result of the big misfit between the implanted layer and the bulk crystal.
9:00 PM - C9.8
Sol-gel Synthesized Ferroelectric Nanoparticles Investigated by Piezoresponse Force Microscopy.
Tobias Jungk 1 , Florian Johann 1 , Akos Hoffmann 1 , Elisabeth Soergel 1 , Susanne Lisinski 2 , Lorenz Ratke 2
1 University of Bonn, Institute of Physics, Bonn Germany, 2 Institute of Material Physics in Space, DLR, Cologne Germany
Show AbstractLithium niobate (LiNbO3) and lithum tantalate (LiTaO3) crystals are intensively investigated due to their outstanding nonlinear optical properties. The capability of producing nanoparticles out of those materials has even expanded the number of possible applications with random quasi-phase-matching being probably the most illustrious candidate. For the fabrication of nanoparticles two approaches are in general possible: top-down (milling of crystals) and bottom-up (sol-gel growth). The advantages of the top-down approach are obvious: one can precisely chose the material (stoichiometry, composition, doping), and one can conduct comparative experiments with bulk crystals. However, up to now, milling of crystals for the production of reasonable amounts of nanoparticles has not been successful. We therefore chose the bottom-up approach synthesizing LiNbO3 (and LiTaO3) nanoparticles by the sol-gel method from a precursor solution of lithium- and niobium (tantalum)-ethoxide. The particle size has been controlled by varying sinter temperature and sinter time. In order to characterize the nanoparticles and optimize the fabrication procedure three main questions were to be answered: (1) Are those nanoparticles ferroelectric? (2) Can single nanoparticles be poled? (3) Can we influence the direction of polarization?(1) Statistical analysis of large PFM images (30 x 30 μm2) of small particles (> 200 nm) and comparison with samples containing on purpose a determined amount of ballast (i. e. non-ferroelectric particles) allowed us to confirm the ferroelectric properties of all LiNbO3 and LiTaO3 nanoparticles. (2) Poling of single nanoparticles was performed with the help of the PFM tip. Applying a voltage to it reverses the polarization of the nanoparticle underneath the tip. We observed partial poling of nanoparticles but we never observed simultaneous poling of adjacent particles. (3) Comparing PFM images recording the in-plane and the out-of-plane deformation of the nanoparticles we can clearly attribute the polarization direction to every particle. We therefore recorded two images of the same area with the sample being rotated by 90° in between. For the latter we used a high-precision rotation stage. Adjusting the of the axis rotation with respect to the tip we obtained a shifting of the image by a few µm for a 90° rotation. Samples fabricated so far show no preferred direction of the polarization of the nanoparticles. By applying a homogeneous electric field during the fabrication procedure we expect, however, to be able to influence also this property.
9:00 PM - C9.9
The Role of Non-planar Surface Geometries in Ferroelectric Nanostructures.
Rajeev Ahluwalia 1 , Nathaniel Ng 1 , David Srolovitz 2
1 , Institute of High Performance Computing, Singapore Singapore, 2 , Yeshiva University, New York, New York, United States
Show Abstract
Symposium Organizers
Charles Ahn Yale University
Philippe Ghosez Universite de Liege
Masashi Kawasaki Tohoku University
Darrell Schlom Cornell University
Jean-Marc Triscone University of Geneva
C10: Novel Multiferroic Materials and Heterostructures
Session Chairs
Thursday AM, December 04, 2008
Room 210 (Hynes)
9:30 AM - C10.1
Solution Processed Multiferroic Nanostructures through Block Copolymer Self-Assembly.
Shenqiang Ren 1 , Robert Briber 1 , Manfred Wuttig 1
1 Materials and Science Engineering Department, University of Maryland at College Park, College park, Maryland, United States
Show AbstractThe recent renaissance of Magnetoelectrics(MEs) was spurred by the discovery of novel natural MEs and the expectation that large interaction coefficients could be achieved with ME composites (MECs). The highest degree of self-organization has been achieved by 3D epitaxial fabrication of 1-3 MECs. The self-organizing capabilities of diblock copolymers are well known and have been used increasingly to synthesize highly ordered photonic, electronic and acoustic nano-structures. This presentation reports on the successful synthesis and characterization of a two-phase multiferroic nano-composite that was achieved through the simultaneous templating of two separate inorganic phases from two sol/gel precursors. Choosing ferromagnetic cobalt ferrite and ferroelectric lead zirconium titanate as the two inorganics resulted in a self-organized magnetoelectric 1-3 nanocomposite whose initial magnetic permeability can be changed by a factor of five through the application of 2.5V compatible with telecommunication applications.
9:45 AM - C10.2
Layered Magnetoelectric Composites Performance Optimization.
Grygoriy Kravchenko 1 , D. Pan 2 , Alex Volinsky 1
1 Mechanical Engineering, University of South Florida, Tampa, Florida, United States, 2 School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing China
Show AbstractLayered multiferroic materials exhibit unique coupling between ferroelectric and ferromagnetic phases, which produces new magnetoelectric (ME) or magnetodielectric effects, providing means of energy transformation. One can tailor composite geometry to maximize the ME effect. For example, cylindrical layered composites exhibit better ME performance than the planar ones. This paper reports on the mechanical interactions between the piezomagnetic and the piezoelectric layers in cylindrical and planar composites. Both experimental and modeling results provide an opportunity for geometry optimization and ME performance enhancement.
10:00 AM - C10.3
The First-principles Study of Polarization Behaviors in PbTiO3/BaTiO3 Superlattices.
Zhu ZhenYe 1 , Zhang XingHong 1 2 , Zhang HuaYu 1
1 , Harbin Institute of Technology Shenzhen Graduate School, ShenZhen China, 2 Center for Composite Materials, Harbin Institute of Technology , Harbin China
Show Abstract10:15 AM - C10.4
Complex Phase Mixture and Domain Superstructure across a New Lead-free Ferroelectric/Antiferroelectric Morphotropic Phase Boundary.
Ching-Jung Cheng 1 , Sung-Hwan Lim 2 , Warren McKenzie 1 , Shigehiro Fujino 2 , Ibrahim Burc Misirlioglu 3 , Paul Munroe 1 , Lourdes Salamanca-Riba 2 , Ichiro Takuechi 2 , Nagarajan Valanoor 1
1 School of Materials Science, University of New South Wales, Sydney, New South Wales, Australia, 2 Dept of Materials Science and Engg, Univ of Maryland, College Park, Maryland, United States, 3 , Max-Planck Institute, Halle Germany
Show Abstract10:30 AM - C10.5
Properties of Periodically Ordered Magnetic Multiferroic CoFe2O4/Pb(Zr,Ti)O3 Heterostructure Nanodot Arrays and Nanocomposites.
Xingsen Gao 1 , L. Liu 1 , W. Lee 1 , B. Birajdar 1 , B. Rodriguez 1 , M. Zieze 2 , M. Alexe 1 , D. Hesse 1
1 , Max-Planck Institute of microstructure physics, Halle Germany, 2 Div. of Superconductivity and Magnetism, Univ. of Leipzig, Leipzig Germany
Show Abstract10:45 AM - C10.6
Epitaxial BiFeO3 - BaFeO3-x Interfaces and Alloys.
Charlee Callender Bennett 1 2 , Dae Ho Kim 2 3 , Hans Christen 2 , David Norton 1
1 Department of Materials Science and Engineering, University of Florida, Gainesville, Florida, United States, 2 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 3 Department of Physics, Tulane University, New Orleans, Louisiana, United States
Show AbstractBaFeO3-x can be epitaxially stabilized in a cubic perovskite structure. When fully oxidized (x=0), it exhibits ferromagnetism (Fe4+), while as-grown films (BaFeO2.5) contain the same Fe3+ sublattice as BiFeO3. Epitaxial heterostructures containing both BaFeO3-x and BiFeO3 can be formed by pulsed-laser deposition, as can alloys of (Ba1-zBiz)FeO3-y (over the range of 0 ≤ z ≤ 1). This presents new opportunities for fully epitaxial multifunctional structures. In this contribution, we discuss the ferroelectric and magnetic properties of (Ba1-zBiz)FeO3-y thin films and related heterostructures. The effects of oxygen content on the magnetic, dielectric, and transport properties is examined, controlling oxidation conditions during growth and with post-growth annealing. The effects of epitaxial strain are discussed, where strain is controlled via epitaxial growth on single crystal perovskite substrates with different lattice parameters. Finally, the effects of the Ba:Bi ratio on magnetic and dielectric behavior is presented.Research sponsored by the Army Research Office and the Division of Materials Sciences and Engineering, Basic Energy Sciences, U.S. Department of Energy.
11:30 AM - **C10.7
Ferroic Nanodomains in Epitaxial Thin Films.
B. Noheda 1 , G. Rispens 1 , A. Vlooswijk 1 , C. Daumont 1 , D. Rubi 1 , G. Catalan 1
1 Zernike Institute for Advanced Materials, University of Groningen, Groningen Netherlands
Show AbstractIn recent years the role of epitaxial strain in ferroic oxides is being uncovered. This is bringing attractive possibilities for the downsizing of ferroelectrics and multiferroics and the modification of their physical properties. But still now, the problem of controlling and fine-tuning the domain configuration and properties of the films in a reproducible way remains elusive. The major role played by the growth conditions and the substrate properties, beyond the well-established lattice mismatch, which are difficult to include in the theoretical models, is responsible for much of this. In this talk, the use of epitaxial strain for the growth of thin ferroelectric and multiferroic materials and the effect on their properties will be discussed, with emphasis on the above mentioned issues. We have chosen the classical tetragonal perovskite ferroelectric of PbTiO3, which is well-known to show a large strain-polarization coupling. PbTiO3 thin films have been grown both by Pulsed Laser Deposition and Molecular Beam Epitaxy on SrTiO3 (compressive strain) and DyScO3 (tensile strain) substrates. The influence of growing above or below TC on the ferroelectric properties has been investigated by tuning TC via Sr-doping. Thin films of PbTiO3 have also been grown on DyScO3 substrates. In this case, due to the small mismatch at the growth temperature, high-quality paraelectric thin films can be grown. Upon cooling down through TC, strain develops and periodic ferroelectric domains form. The degree of control achieved in this way is thus greater than in the cases when the mismatch in the paraelectric phase also plays a role. The thinnest of these films (d< 8nm) display 180o periodic domains due to the large depolarizing fields, whereas the thicker films (d>28nm) consist of 90o domain patterns determined by the elastic energy. The observed dependence of the domain periodicity with the film thickness has also revealed the energetics of domain wall formation. For intermediate thicknesses, the crossover from 180o to 90o domains is observed. For this crossover, a model is proposed that gives rise to ferroelectric closure-like domains. For materials with lower symmetries and more complex functional behaviour, such as the multiferroic orthorhombic perovskites of TbMnO3 and YbMnO3, the role of epitaxial strain has been less investigated. These thin film materials are barely discussed in the literature because the synthesis of single phase, stoichiometric, strained films presents a major challenge. We have investigated the complex domain configurations that are formed in these materials in order to keep the coherence with the substrate and how they evolve with thickness. The effect of epitaxial strain on the physical properties has been found to be major in the case of TbMnO3, due to the subtle interplay between the crystal structure and the spin structure in this multiferroic.
12:00 PM - C10.10
Investigation of MgO(111) Template Layer for Effective Integration of Functional Oxides with Hexagonal Silicon Carbide.
Katherine Ziemer 1 , Trevor Goodrich 1 , Zhuhua Cai 1
1 Chemical Engineering, Northeastern University, Boston, Massachusetts, United States
Show AbstractEffective integration of multiple functional oxide layers on a semiconductor platform can enable dynamic tuning of device properties by linking the functionalities of the separate oxides, such as through magnetoelastic coupling. Integration of the functional oxide structure on a wide bandgap semiconductor platform can accommodate the high-frequency, high-power, harsh environment, and multi-functionality demands of next generation devices. One challenge to realize this integration is the large lattice mismatch between the wide bandgap semiconductor and the functional oxides. Through molecular beam epitaxy (MBE), the use of a magnesium oxide (MgO) template layer and the interface formation mechanisms of an oxygen bridge have been investigated for effective heteroepitaxy of high-quality ferroelectric barium titanate (BTO) on 6H-SiC.6H-SiC(0001) substrates are cleaned in an ex-situ hydrogen furnace which produces and atomically smooth, stepped surface with a √3×√3 R30ο surface reconstruction, verified by reflection high energy electron diffraction (RHEED) and x-ray photoelectron spectroscopy (XPS). High quality, single crystalline MgO(111) is obtained with a smooth surface (RMS<0.5 nm) and a stepped morphology conformal to the underlying 6H-SiC morphology, but is inherently twinned due to the ionic nature of a (111) oriented rock salt structure. The smooth, conformal 2-D growth mechanism of MgO prefers to grow in tension with a 3.3% lattice mismatch, requires the presence of atomic oxygen, and transitions to a more 3-D growth mode when the thickness reaches ~10 nm. The engineered Mg) surface is both effective and necessary to promote the pseudo-hexagonal heteroepitaxy of BTO(111). Similar to MgO, BTO(111) prefers to grow in tension with a 5.3% lattice mismatch and is inherently twinned with a 6-fold symmetry due to 60ο in-plane rotations. The resulting epitaxy alignments for the BTO/MgO/6H-SiC results in a BTO{111}//MgO{111}//6H-SiC{0001} out-of-plane relationship and a BTO{11(bar)0}//MgO{11(bar)0}//6H-SiC{002(bar)1} in-plane relationship. The BTO layer of the heterostructure has ferroelectric properties with a saturated polarization around 4.7 μC/cm2 and an apparent striped domain structure.
12:00 PM - C10.8
Large Area Epitaxial Ferroelectric Nano-capacitor Arrays with Near Tb/in2 Density.
Hee Han 2 , Woo Lee 3 1 , Andriy Lotnyk 1 , Markus Andreas Schubert 1 , Stephan Senz 1 , Dietrich Hesse 1 , Marin Alexe 1 , Sunggi Baik 2 , Ulrich Goesele 1
2 Materials Science & Engineering, Pohang University of Science and Technology, Pohang Korea (the Republic of), 3 , Korea Research Institute of Standards and Science , Daejon Korea (the Republic of), 1 , Max Planck Institute of Microstructure Physics, Halle Germany
Show Abstract12:00 PM - C10.9
Topotactic Anion Exchange – A Route to Epitaxial Oxide Integration.
Mark Zurbuchen 1 , Darrell Schlom 2
1 Microelectronics Technology Dept, The Aerospace Corporation, El Segundo, California, United States, 2 Dept of Materials Science and Engineering, Cornell University, Ithaca, New York, United States
Show Abstract12:15 PM - C10.11
Epitaxial Integration of Ferroelectric Oxides on GaN.
Elizabeth Paisley 1 , Mark Losego 1 , Spalding Craft 1 , Amit Kumar 2 , Venkatraman Gopalan 2 , Jon-Paul Maria 1
1 Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina, United States, 2 Materials Science and Engineering, The Pennsylvania State University, State College, Pennsylvania, United States
Show AbstractEpitaxial integration of the ferroelectrics PbxZr1-xTiO3 (PZT) and BaTiO3 (BT) with wide band gap polar semiconductors such as GaN (0002) presents the possibility of electrostatically coupling the polarization vectors of these dissimilar materials. Further, the re-orientable nature of the ferroelectric dipole will allow the interface charge that must accompany the interfacial polarization discontinuity to be systematically modulated. Consequently, a new generation of smart transistors that are non-volatile, and simultaneously respond to electrical, thermal, or mechanical stimuli are envisioned. This presentation will describe the synthesis and characterization of these thin film heterostructures by magnetron sputtering, with specific attention given to process optimization. Using x-ray diffraction (XRD) and electrical characterization, the growth of epitaxial PZT and BT films directly on GaN was verified. In parallel, epitaxial PZT films were also grown on GaN with wide bandgap rocksalt buffer layers (~5 nm thick) such as MgO. A two stage growth process was developed for epitaxial PZT which required a deposition temperature of 300 oC and an ex-situ anneal at 650 oC. This combination was effective in mitigating interfacial reactions and promoting phase-pure perovskite growth. Films were grown to a target thickness of 85 nm. Electrical analysis of interdigital capacitors revealed a nonlinear and hysteretic dielectric response consistent with ferroelectric PZT. Piezoelectric force microscopy characterization has shown the films to be uniformly poled in the as-deposited state, evidence of ferroelectric switching, and suggests a high charge density at the PZT/GaN interface and coupling between the PZT and GaN polarization vectors. Current efforts continue to focus on electrical characterization and piezoelectric force microscopy characterization of these materials systems. The outcomes of these measurements and a comparison of structures with and without buffer layers will be presented.
C11: Polarization Catastrophe
Session Chairs
Thursday PM, December 04, 2008
Room 210 (Hynes)
2:30 PM - C11.1
Electrostatic Doping in Oxide Heterostructures.
Alex Demkov 1 , Jaekwang Lee 1
1 Department of Physics, The University of Texas, Austin, Texas, United States
Show AbstractRecent experiments on perovskite heterostructures grown by molecular beam epitaxy or pulsed laser deposition suggest the creating high mobility two dimensional electron gas and even a superconducting state at the oxide/oxide interface. However, the origin of charge in these insulating materials is still not clear and deemed controversial. We report a first-principles study of SrTiO3/LaAlO3 heterostructures using density functional theory at the LDA+U level. We consider the energetics and electronic structure of the junction, while focusing on the role of electrostatics. Our results suggest that a complex balance of the crystal filed, Jahn-Teller effect, lattice dynamics and internal electric field result in the robust electrostatic doping for carefully chosen thickness of the polar oxide. We explore the possible uses of this effect in other oxide-based heterostructures.
2:45 PM - C11.2
Intermixing at DySc3/SrTiO3 Interfaces.
Martina Luysberg 1 , Jürgen Schubert 2 , Markus Heidelmann 1 , Lothar Houben 1 , Tassilo Heeg 3 2
1 ER-C and IFF, Research Center Jülich, Jülich Germany, 2 IBN and CNI, Research Center Jülich, Jülich Germany, 3 MSE, Cornell University, Ithaca, New York, United States
Show AbstractRecently, the interfaces between polar and non-polar oxides have attracted much attention because two-dimensional electron gases can be established. This implies potential device applications such as high electron mobility field effect transistors. The most prominent example is the interface beween SrTiO
3 (STO) and LaAlO
3 (LAO), where a change of valancy of titanium at the interface has been observed, which was attributed to oxygen vacancies. This accounts for an extra charge of ½ at the interface necessary to avoid a polar catastrophe. Here we report on structural and spectroscopic investigations on the interface between STO and DyScO
3 (DSO), where the latter exhibit the same polarity as LAO.
Multilayers of DSO/STO were grown by pulsed laser deposition on various substrates, i.e. Si, STO and DSO. High resolution high-angle annular dark field (HAADF) images were recorded in an aberration corrected Titan 80-300 with a beam diameter below 0.1 nm. These images were used to determine the Dy concentration on an atomic scale. The Ti and Sc concentrations were measured by electron energy loss spectroscopy (EELS), with a beam diameter of about 0.1- 0.2 nm. Simultaneously, HAADF images were recorded in order to assign the EELS Spectra to individual atomic layers. As a result both, the Dy/Sr and Sc/Ti sublattices show an intermixing over about 2-3 atomic layers at the interfaces. The consequences of this intermixing will be discussed in view of the charge distribution at the interface.
3:00 PM - C11.3
A First Principle Study of LaAlO3/SrTiO3 Heterointerfaces.
Hanghui Chen 1 3 , Alexie Kolpak 2 3 , Sohrab Ismail-Beigi 1 2 3
1 Department of Physics, Yale University, New Haven, Connecticut, United States, 3 Center for Research on Interface Structures and Phenomena (CRISP), Yale University, New Haven, Connecticut, United States, 2 Department of Applied Physics, Yale University, New Haven, Connecticut, United States
Show AbstractIn order to understand the origin of the intriguing high-mobility quasi two dimensional electron gas formed at LaAlO3/SrTiO3(001) heterointerfaces, we carry out first principle calculations on the electronic structure and properties of these oxide interfaces. The intrinsic polar properties are investigated and the average electronic potential increase by each LaAlO3 layer is calculated, which can account for the recent observed fact that the heterointerfaces are not metallic until the LaAlO3 film reaches a critical thickness. When the interface becomes metallic,the spatial distributions of mobile electrons and holes reveal a fundamental asymmetry between the n-type and p-type interfaces, which may provide an explanation for the observed drastic difference in conductivities of thesetwo types of interface. A large cation-cation hopping matrix element across the interface which only exists at the n-type interface turns out to be the key reason for this asymmetry.
3:15 PM - C11.4
Electric Field Control of the LaAlO3/SrTiO3 Interface Ground State.
Stefano Gariglio 1 , Andrea Caviglia 1 , Nicolas Reyren 1 , Toni Schneider 2 , Marc Gabay 3 , Stephan Thiel 4 , German Hammerl 4 , Jochen Mannhart 4 , Jean-Marc Triscone 1
1 DPMC, University of Geneva, Geneva Switzerland, 2 Physikinstitut, University of Zurich, Zurich Switzerland, 3 Laboratoire de Physique des Solides, Universite Paris-Sud 11, Paris France, 4 Institute of Physics, University of Augsburg, Augsburg Germany
Show AbstractAt interfaces between complex oxides, electronic states with unusual properties can be promoted. A particularly fascinating system is the interface between band insulators LaAlO3 and SrTiO3, which displays conductivity with high mobility. Recently two possible ground states have been experimentally identified: a two dimensional superconducting condensate and a magnetic state. In this presentation field effect experiments performed on this system will be discussed. Using the electrostatic tuning of the carriers density the phase diagram of the system has been explored, revealing a quantum phase transition from a 2D superconducting state to a insulating state. The insulating phase is characterized by a strong negative magnetoresistance, possible signature of weak localization. Down to 30 mK, no magnetism has been detected.
C12: Novel Characterization Techniques
Session Chairs
Thursday PM, December 04, 2008
Room 210 (Hynes)
4:00 PM - C12.1
Global and Local Polarization by Switching Spectroscopy Piezoforce Microscopy in Ferroelectric Thin Films.
Patamas Bintachitt 1 , Susan Trolier-McKinstry 1 , Katyayani Seal 2 , Stephen Jesse 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, Oak Ridge, 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 -12.4 C/m2 and -10.0 C/m2 were achieved for PZT thin films of 1.0 μm and 0.24 μm thickness, respectively. The polarization behavior in both polycrystalline and {100} textured films was studied through first order polarization reversal methods in order to assess the global Preisach distribution governing switching with large area electrodes. These results were then compared to switching spectroscopy piezoresponse force microscopy (PFM) with uniform fields to map the localized response. The switchable polarization as a function of bias window allows the voltage dependence and spatial distribution of regions with reversible and irreversible wall motion to be mapped. Reasonable agreement between the two methods was obtained, suggesting that it may be possible to develop a quantitative understanding of how local structure influences switching.
4:15 PM - C12.2
Direct Imaging of Spatial Variations of Switching Parameters in Micrometer Scale Ferroelectric Capacitors.
Dong Wu 1 , I. Kunishima 2 , S. Roberts 3 , A. Gruverman 3
1 Physics, North Carolina State University, Raleigh, North Carolina, United States, 2 , Toshiba Corporation, Yokohama Japan, 3 , University of Nebraska-Lincoln, Lincoln, Nebraska, United States
Show AbstractInvestigation of the switching behavior of micrometer scale capacitors is important both for fundamental understanding of the scaling effect in ferroelectrics and for development of high-density ferroelectric-based memory technology. Ferroelectric polarization reversal, which can be considered as a first-order phase transition, is controlled by nucleation probability and domain wall velocity. However, with decrease in capacitor size contribution of the nucleation mechanism will change resulting in stronger contribution of the lateral domain growth and increased electrode perimeter effect. In this paper, we develop an approach to visualize the domain evolution in microscale capacitors as a function of an applied electrical field with nanoscale spatial resolution. This method, based on piezoresponse force microscopy (PFM), allows direct imaging of spatial distribution of local switching parameters, and delineation of nucleation and lateral domain growth mechanisms contribution into polarization reversal process. (001)-oriented 100 nm thick MOCVD-grown PZT films were used to fabricate capacitor structures with the lateral dimensions in the range from several micrometers down to several hundred nanometers by means of reactive ion etching. A set of spatially resolved PFM images of PZT capacitors obtained at an incrementally increasing external field provides information on domain-microstructure interactions during polarization reversal as well as on capacitor size effect on domain dynamics. Local switching spectroscopic measurements performed during scanning over the capacitor area were related to the sequence of PFM images reflecting domain evolution to clarify the fine structure of the local hysteresis loops and their relation to the integral polarization hysteresis loop. The developed approach can be applied to delineate the spatial distribution of nucleation sites and pinning centers, activation energy and built-in fields and relate them to local capacitor microstructure and to capacitor size
4:30 PM - C12.3
Spin-Charge-Lattice Coupling through Multi-Magnon Excitations in Multiferroic BiFeO3.
Amit Kumar 1 , Sava Denev 1 , Mariola Ramirez 1 , Jon Ihlefeld 1 , Darrell Schlom 1 , Lane Martin 2 , Ying-Hao Chu 2 , Ramamoorthy Ramesh 2 , Joe Orenstein 3 , Alexander Litvinchuk 5 , Janice Musfeldt 4 , Venkatraman Gopalan 1
1 Materials Science and Engg., Pennsylvania State University, University Park, Pennsylvania, United States, 2 Materials Science and Engg., University of California Berkeley, Berkeley, California, United States, 3 Materials Science Divison, Lawrence Berkeley National Lab, Berkeley, California, United States, 5 , University of Houston, Houston, Texas, United States, 4 Department of Chemistry, University of Tennessee, Knoxville, Tennessee, United States
Show AbstractSpin-charge-lattice coupling mediated by multi-magnon processes is demonstrated in multiferroic BiFeO3. Raman, linear and non linear optical spectroscopies [1-3] show up to five resonant enhancements of the 2-magnon excitation below the Neel temperature. These are shown to be collective interactions between on-site Fe d-d electronic resonance, phonons and multimagnons. These resonances are also observed in the temperature dependence of multimagnon sidebands to electronic levels using nonlinear optical spectroscopy. Combined multi-magnon, electronic and vibrational spectroscopies have been used to sensitively reveal coupled phenomena in multiferroics, particularly where distinguishing magnetic and polar order parameters is a challenge.
[1] “Two-phonon coupling to the antiferromagnetic phase transition in multiferoic BiFeO3” Appl. Phys. Lett. 92, 022511 (2008)
[2] “Linear and nonlinear optical properties of BiFeO3” Appl. Phys. Lett. 92, 121915 (2008)
[3] “Spin-Charge-Lattice Coupling through Multi-Magnon Excitations in Multiferroic BiFeO3” arXiv:0803.3473 (March 2008)
4:45 PM - C12.4
Nanoscale Mapping of Nucleation and Growth Activation Energies for Individual Ferroelectric Domains.
Ramesh Nath 1 , Nicholas Polomoff 1 , Ramamoorthy Ramesh 2 , Bryan Huey 1
1 Materials Science and Engineering, University of Connecticut, Storrs, Connecticut, United States, 2 Materials Science and Engineering, University of California, Berkeley, Berkeley, California, United States
Show AbstractThe unique properties of ferroelectric perovskite thin films have been employed in several modern devices, but with the continuing trend towards miniaturization the microstructural influence on ultimate device performance is an increasingly important issue. Accordingly, this work focuses on mapping individual domain switching dynamics by performing a newly developed high speed variation of Piezoresponse Force Microscopy to uniquely investigate switching dynamics at the requisite nanoscale resolution. Specifically, complete image acquisition (256*256 pixels or better) with <20nm spatial resolution is achieved continuously in 6.4 seconds per frame. The resulting movies, comprising hundreds of consecutive images all acquired in a matter of minutes, provide significant statistical data on the switching dynamics by nucleation and growth mechanisms. The mechanism and kinetics involved in the dynamic domain switching process of epitaxial PZT thin films are therefore presented with nanoscale and microsecond resolution. This provides a spatially resolved analysis of nucleation and growth kinetics based on tracking thousands of individual domain locations, areas, nucleation times, and growth rates. Initial results show that domain dynamics processes are governed by the spatial distribution of inhomogeneities present in the film. Notably, for the same location, these high speed PFM measurements are repeated with a variety of electric fields. This uniquely allows the evolution of domain switching to be related to the energetics of any film defects in the field of view. Ultimately, an exponential behavior with electric field is observed for individual domain growth, and inversely for nucleation time. From this data, activation energies are extracted and mapped for the nucleation and growth of individual domains.
5:00 PM - C12.5
Nanoscale Piezoresponse Studies of Ferroelectric Domains in Epitaxial BiFeO3 Nanocapacitors Defined by Focused Ion Beam Lithography.
Seungbum Hong 1 , Jeffrey Klug 1 3 , Moonkyu Park 1 5 , Michael Bedzyk 1 3 4 , Kwangsoo No 5 , Amanda Petford-Long 1 , Orlando Auciello 1 2
1 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States, 3 Department of Physics and Astronomy, Northwestern University, Evanston, Illinois, United States, 5 Department of Materials Science and Engineering, KAIST, Seoul Korea (the Republic of), 4 Materials Science Department and Materials Reasearch Center, Northwestern University, Evanston, Illinois, United States, 2 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, United States
Show Abstract5:15 PM - C12.6
Probing Spin-Lattice Correlations in the Hexagonal RMnO3 System.
Trevor Tyson 1 , Zhiqiang Chen 1 , Catherine Dubourdieu 2 , Isabelle Gelard 2 , San-Wook Cheong 3
1 , New Jersey Inst. Tech., Newark, New Jersey, United States, 2 , LMGP, CNRS, Grenoble France, 3 , Rutgers University, Piscataway, New Jersey, United States
Show Abstract5:30 PM - C12.7
Direct Measurements of Individual Ferroelectric Domain Switching as a Function of Electrode Geometry and Pre-existing Domain Structure.
Nicholas Polomoff 1 , James Bosse 1 , Atif Rakin 1 , Ramamoorthy Ramesh 2 , Bryan Huey 1
1 Institute of Materials Science, University of Connecticut, Storrs, Connecticut, United States, 2 Materials Science and Engineering, University of California, Berkeley, Berkeley, California, United States
Show Abstract5:45 PM - C12.8
Antiferromagnetic Spin Polarization of Individual Domains in (001) BiFeO3 Thin Films.
Rebecca Sichel 1 , Alexei Grigoriev 1 , Daniel Ortiz 1 , Rasmi Das 1 , Chang-Beom Eom 1 , Zhonghou Cai 2 , Paul Evans 1
1 Materials Science Program, University of Wisconsin, Madison, Madison, Wisconsin, United States, 2 Advanced Photon Source, Argonne National Labs, Argonne, Illinois, United States
Show Abstract
Symposium Organizers
Charles Ahn Yale University
Philippe Ghosez Universite de Liege
Masashi Kawasaki Tohoku University
Darrell Schlom Cornell University
Jean-Marc Triscone University of Geneva
C13: Domain Structure and Dynamics
Session Chairs
Friday AM, December 05, 2008
Republic B (Sheraton)
9:30 AM - C13.1
The Influence of the Screening Effect on Domain Configuration in BiFeO3 Thin Films.
Christopher Nelson 1 , Xiaoqing Pan 1 , SeungHyub Baek 2 , Chang-Beom Eom 2
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
Show AbstractMultiferroics simultaneously exhibiting ferroelectric and ferro/antiferromagnetic order have been the subject of considerable research due to their potential use in novel magnetoelectric devices. Of the few single-phase materials which exhibit this dual behavior BiFeO3 has received the most attention due largely to its large polarization (90μC cm-2) and high Neel (~650K) and Curie (~1040K) temperatures. The ferroelectric properties of BiFeO3 depend on its domain structure. The domain configuration will vary with choice of substrate surface, film thickness, growth method and temperature, and the screening effect (or lack thereof) at the interfaces. The later refers to the presence of free charges at the film surface which act to stabilize out of plane polarization. In this work we systematically study the influence of this screening effect by studying BFO thin films with varying electrode configurations while keeping the other parameters constant. Four 200nm BFO films were studied: two with both top and bottom electrodes, one with the bottom electrode only, and one having no electrodes. Bottom electrodes were all 100nm SrRuO3 and of the two top electrodes one was 50 nm SrRuO3 and the other was 50nm platinum. All films were grown on 4 degree miscut (001) SrTiO3 substrates. The domain structure was characterized by cross sectional transmission electron microscopy. The differences observed in the domain configurations of these films as a result in the changes in screening effect is discussed.
9:45 AM - C13.2
Structure and Energetics of Domain Walls in LiNbO3 by Atomic-Level Simulation.
Donghwa Lee 1 , Haixuan Xu 1 , Venkatraman Gopalan 2 , Volkmar Dierolf 3 , Simon Phillpot 1
1 Department of Materials Science and Engineering, University of Florida, Gainesville, Florida, United States, 2 Department of Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania, United States, 3 Department of Physics , Lehigh University, Bethlehem, Pennsylvania, United States
Show Abstract10:00 AM - C13.3
Investigations of Ferroelectric Domains on All Crystal Faces of Lithium Niobate Single Crystals using Scanning Force Microscopy.
Tobias Jungk 1 , Akos Hoffmann 1 , Elisabeth Soergel 1
1 University of Bonn, Institute of Physics, Bonn Germany
Show AbstractWe present a full analysis of the contrast mechanisms for the detection of ferroelectric domains on all (x-, y-, and z-) faces of bulk single crystals using scanning force microscopy. The experiments were carried out with hexagonally poled lithium niobate to have access to a well defined domain structure on every crystal face. The domain contrast can be attributed to three different mechanisms: i) the thickness change of the sample due to an out-of-plane piezoelectric response (standard piezoresponse force microscopy), ii) the lateral displacement of the sample surface due to an expanding-contraction-movement, and iii) the electrostatic tip-sample interaction at the domain boundaries caused by surface charges on the crystallographic y- and z-faces. Interestingly, we could not observe any shear movement of the sample surface but his deformation turned out to be strongly suppressed by clamping. Note that the lateral displacement ii) is due to the fact that although the electric field from the tip is rotational symmetric, the effect of opposed components of the electric field do not cancel out. Quite the contrary takes place: they lead to an expansion on one side and a contraction on the other side resulting in a net sliding movement of the sample surface underneath the tip. In order sustain the driving mechanisms proposed above we performed angle-resolved measurements on every crystal face. We therefore upgraded our experimental setup with a PC-controlled high-precision rotation stage on top of which the sample was mounted. This improved setup allowed us to determine the direction of the in-plane surface displacements on every crystal face by rotating the sample while measuring the torsion of the cantilever. A careful analysis of the movements of the cantilever with respect to its orientation relative to the crystallographic axes of the sample allowed a clear attribution of the observed domain contrast to the driving forces.
10:15 AM - C13.4
Monodomain to Multidomain Transitions Induced by Depletion Layers in Ferroelectric Thin Films.
Nathaniel Ng 1 , Rajeev Ahluwalia 1
1 Materials Theory & Simulation Laboratory, Computational Materials Science, Institute of High Performance Computing, Singapore Singapore
Show AbstractWhile it has been shown that non-ferroelectric "dead" layers play a significant role due to the bound charges, we show that free charge surface layers can play an equally important role. A depletion layer at the interface between the ferroelectric and metallic electrode can form due a difference in the work function of the semiconductor and the electrodes, resulting in a built-in electric field which influences the polarization profile in the material. This investigation applies the time-dependent Ginzburg-Landau framework to study fully and partially-depleted thin films of BaTiO3 with varying amounts of space charge and film thicknesses. We show that these layers significantly influence the switching process as well as the remnant polarization in the film. An increase in the space charge density results in a domain instability with the formation of wedge-like domain structures in the space charge layer. At sufficiently small thicknesses, a single-domain remnant state can no longer be maintained and 180° striped domain structures are observed. This results in a reduction in the remnant polarization as a function of both space charge density as well as thickness. We also simulate the polarization switching process and show that the built-in electric field serves to lower the nucleation barrier for switching.
10:30 AM - C13.5
Field-Coupled Mechanics of Domain Structure Evolution in Ferroelectric Thin Film Capacitors.
William Oates 1 , Alexei Gruverman 2
1 Mechanical Engineering, Florida A&M/Florida State University, Tallahassee, Florida, United States, 2 Physics, University of Nebraska-Lincoln, Lincoln, Nebraska, United States
Show AbstractFerroelectric materials are important electronic materials for many industrial, aerospace, and biomedical applications. A strong understanding of the underlying domain structure evolution and crystal anisotropy is important to effectively utilize these materials in applications. Here, we report on recent observations of abnormal ferroelectric switching in lead zirconate titanate (PZT) thin film capacitors using piezoresponse force microscopy (PFM) and correlate this behavior with non-equilibrium, finite element phase field modeling. (111)-oriented 200 nm thick sputtered PZT films were formed into capacitor islands of several square micrometers using reactive ion etching. The obtained results show that the top electrode has a dramatic effect on polarization retention leading to increased polarization instability with an increase in the electrode thickness. Theoretical elasticity techniques and finite element phase field analysis illustrate key electro-mechanical material mechanisms associated with this unusual polarization retention behavior. It is shown that the crystal growth orientation, interface residual stress imposed by the top electrode in combination with charge compatibility along domain walls contribute to polarization instability in PZT capacitors. Elasticity techniques are then used to illustrate scaling relations that correlate capacitor size with reverse switching driving forces. The observed behavior and underlying field-coupled mechanics should be taken into account to avoid reliability issues in these electronic structures.
10:45 AM - C13.6
Phase-Field Simulations of Local Ferroelectric DomainSwitching in Piezoresponse Force Microscopy.
Samrat Choudhury 1 2 , Jingxian Zhang 2 , Sergei Kalinin 3 , Long Chen 2
1 Materials Science and Enginnering, University of Wisconsin, Madison, Madison, Wisconsin, United States, 2 Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania, United States, 3 The Center for Nanoscale Materials Sciences and Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractMesoscopic ferroelectric behavior, including static domain structures, domain wall and nucleation dynamics, and the role of microstructure on polarization behavior, has attracted much theoretical and experimental interest in the last decade due to rapidly emerging applications in information technologies and MEMS. Piezoresponse Force Microscopy (PFM) has emerged as a primary technique for characterization of ferroelectric behavior on the nanoscale. The primary limitation to date is the dearth of universal data analysis and modeling tools that can be used to analyze PFM data in complex microstructures. In this work, we summarize the recent advancement in phase-field modeling of PFM data in ideal surfaces [1], in the presence of 90 degree ferroelastic twins [2], and well-defined grain boundaries [3]. We developed a three-dimensional (3-D) phase-field model for predicting the evolution of domain structures and domain switching in ferroelectric thin films under a localized applied electric potential. Using lead zirconate titanate (PbZr0.2Ti0.8O3) and bismuth ferrite (BiFeO3) thin films as a model system, we will present the effect of defects such as grain boundaries and twin boundaries on the switching behavior of ferroelectric thin films. It will be shown that the electric potential to nucleate new domains is closely related to the number of twin defects directly below the tip. It is also observed that the presence of non-ferroelectric phase at a grain boundary significantly affects both the domain structure and the switching behavior in the vicinity of the grain boundary. The spatial distribution of nucleation voltages obtained from phase-field approach in presence of these defects is compared to experimental measurements using Piezo-Force Microscope.Acknowledgements:The financial supports from NSF under DMR-0507146 and DMR-0213623(SC, JXZ, and LQC) and from the U.S. Department of Energy under DE-FG02-07ER46417 (S.C. and L.Q.C.) are gratefully acknowledged. Research was sponsored in part (SVK) by the Division of Materials Sciences and Engineering, Office of Basic Energy Sciences, U.S. Department of Energy with Oak Ridge National Laboratory, managed and operated by UT-Battelle, LLC.References:[1] S. V. Kalinin, B. J. Rodriguez, S. Jesse, Y. H. Chu, T. Zhao, R. Ramesh, S. Choudhury, L. Q. Chen, E. A. Eliseev and A. N. Morozovska. Proc. Natl. Acad. Sci.,104, 20204, 2007.[2] S. Jesse, B. J. Rodriguez, S. Choudhury, A. P. Baddorf, I. Vrejoiu, D. Hesse, M. Alexe, E. A. Eliseev, A. N. Morozovska, J. Zhang, L.-Q Chen and S. V. Kalinin. Nature Mater., 7, 209, 2008.[3] B. J. Rodriguez, S. Jesse, K. Seal, A. P. Baddorf, T. Zhao, Y.H. Chu, R. Ramesh, A. Bhattacharyya, A. Eades, S. Choudhury, Long-Qing Chen and Sergei V. Kalinin, to be submitted to Adv. Mater.
11:30 AM - C13.7
Size Dependence Of Crystal Structure And Piezo- And Ferroelectric Properties in Pbtio3 Nanoislands Fabricated on Pt/Srtio3.
Masaru Shimizu 1 , Hironori Fujisawa 1 , Yoshihiro Kuroiwa 2 , Osami Sakata 3 , Jamie Soon 3 , Shigeru Kimura 3 , Minoru Osada 4
1 , University of Hyogo, Himeji, Hyogo, Japan, 2 , Hiroshima University, Higashi-Hiroshima Japan, 3 , JASRI (SPring-8), Sayo Japan, 4 , National Institute for Materials Science, Tsukuba Japan
Show AbstractInterest in size effects in ferroelectrics has increased greatly not only from the point of view of nanoelectronics, but also from that of basic ferroelectric physics. Many studies on size effects in ferroelectric nanoparticles have been discussed. However, there have been few reports on size effects in ferroelectric nanoislands with sizes smaller than 100nm fabricated on substrates.In this paper, we focus on size dependence of crystal structure, phase transition temperature and piezo- and ferroelectric properties in PbTiO3 nanoislands with lateral sizes less than 100nm fabricated on Pt/SrTiO3 (111) and (001) substrates.PbTiO3 nanoislands were fabricated by MOCVD. Lattice parameters were measured using Synchrotron X-ray diffraction (SPring-8). Phase transition temperature and piezo- and ferroelectric properties were examined using Raman spectroscopy and piezoresponse force microscopy, respectively. On Pt/SrTiO3(111) and (001) substrates, pyramidal-shaped islands and square-shaped islands were grown at an initial growth stage, respectively. c-axis lattice constant of PbTiO3(111) nanoislands drastically decreased with decreasing island size from 150nm to 25nm, though a-axis lattice constant did not changed. On the other hand, PbTiO3(001) nanoislands showed no change in c- and a-axis lattice constants. As island size decreased, The phase transition temperature (Tc) of PbTiO3(111) nanoislands decreased from 490 to 420oC. PbTiO3(001) nanoislands showed no size dependence of phase transition temperature. This difference in size dependence of Tc is mainly caused by that in the strain from the substrate.Piezoresponse (d33) in PbTiO3(001) nanoislands also decreased as the size and thickness decreased.
11:45 AM - C13.8
Polarization Vortices in GeTe Nanoclusters.
Engin Durgun 1 , Riad Shaltaf 2 , Xavier Gonze 2 , Philippe Ghosez 1 , Jean-Yves Raty 1
1 Physics, University of Liege, Liege Belgium, 2 PCPM, University of Catholic Louvain, Louvain-la-neuve Belgium
Show AbstractUsing a model Hamiltonian approach, it was predicted that, due to depolarizing field effects, ferroelectric oxide nanodots do no more exhibit a net polarization but instead develop polarization vortices. Here we consider GeTe, an alternative type of ferroelectric material, and investigate the ferroelectric and structural properties of nanodots up to 600 atoms from density functional theory (DFT) first-principles calculations. We demonstrate, for the first time at the DFT level, the existence in the interior of sufficiently large dots of polarization vortices giving rise to a net and reversible toroidal moment of polarization G. The amplitude of G decreases with the size of the system and is totally suppressed below a critical diameter of 2.5 nm. The pattern of atomic distortions and the size evolution of the properties are discussed in relationship with the existence of a surface region within which the atoms behave differently.
12:00 PM - C13.9
Domain Configurations in Ferroelectric Nanoshapes.
Dolan Byrne 1 , Alina Schilling 1 , Gustau Catalan 2 , James Scott 2 , Marty 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 Abstract12:30 PM - C13.11
Spatially Resolved Polarization Switching at an Engineered Defect: Bicrystal Grain Boundary in Bismuth Ferrite.
Brian Rodriguez 1 , Stephen Jesse 1 , Katyayani Seal 1 , Maxim Nikiforov 1 , Arthur Baddorf 1 , Sergei Kalinin 1 , Y. Chu 2 , R. Ramesh 2 , Samrat Choudhury 3 , Long-Qing Chen 3
1 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Dept. of Physics and Dept. of Mat. Sci. and Eng., University of California, Berkeley, California, United States, 3 Department of Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania, United States
Show AbstractPolarization switching in ferroelectric and multiferroic materials is controlled by structural defects that act as nucleation and pinning centers. The progress in the field necessitates the development of fundamental understanding of the atomistic mechanisms of these processes and their relationship with the atomic structure of the defects. Here, we study the ferroelectric polarization switching behavior mediated by the presence of the 24° bicrystal grain boundary (GB) in a multiferroic BiFeO3 epitaxial film. On the mesoscopic scale, Piezoresponse Force Microscopy (PFM) amplitudes across positively and negatively poled GB regions suggest the presence of a frozen polarization component at the interface. The switching experiments demonstrate that the GB attracts the domain wall and acts as a pinning center. The PFM results are compared with conductive atomic force microscopy images, which suggest domain-wall pinning at the GB can be partially attributed to increased conductance at the GB. The GB effect on ferroelectric domain nucleation is studied using the combination of Switching Spectroscopy PFM and phase-field modeling. The GB is shown to affect nucleation biases, resulting in clear feature in nucleation bias maps. In addition, the hysteresis loops in the vicinity of GB develop pronounced fine structure due to domain-defect interactions. The phase field modeling allows establishing the effect of crystallographic mismatch at GB on polarization switching and domain wall pinning, illustrating good agreement with experimental observations. Overall, bicrystal interface is shown to be relatively weak defect that leads to small (less then 30%) changes in nucleation biases. These studies will ultimately allow atomistic understanding of polarization switching processes and role of defect on switching on a single-defect level. Research supported by the Division of Materials Science and Engineering, Basic Energy Sciences, U.S. Department of Energy at Oak Ridge National Laboratory, which is managed by UT-Battelle, LLC.
12:45 PM - C13.12
Phase-field Model of the Relationship of Ferroelectric Hysteresis with Grain Size in Thin Films.
Benjamin Winchester 1 , Long Qing Chen 1 , Samrat Choudhury 1
1 , Pennsylvania State University, University Park, Pennsylvania, United States
Show AbstractA phase-field model was developed for studying the effect of polycrystallinity on the domain size and hysteresis loop of epitaxial ferroelectric thin films. A sixth-order Laundau-Devonshire thermodynamic potential was employed to describe the energy of a polycrystalline PbZr0.8Ti0.2O3 thin film at room temperature. The relative sizes of ferroelectric domains on PbZr0.8Ti0.2O3 thin films under different substrate strains and substrate orientations were obtained and compared. The hysteresis loop of the PZT was found to be affected by the grain size.