Symposium Organizers
Cammy R. Abernathy University of Florida
Salah Bedair North Carolina State University
Pierre Ruterana SIFCOM-ENSICAEN
Rachel Frazier Naval Research Laboratory
K1: Mechanisms and Transport
Session Chairs
Tuesday PM, April 10, 2007
Room 3009 (Moscone West)
9:30 AM - **K1.1
Origin and Control of High Temperature Ferromagnetism in Diluted Magnetic Semiconductors.
Tomasz Dietl 1 2
1 , Institute of Physics, Polish Academy of Sciences, Warszawa Poland, 2 , ERATO Project of JST; Institute of Theoretical Physics, Warsaw University, Warszawa Poland
Show Abstract10:00 AM - **K1.2
Ab initio Materials Design for Room Temperature Ferromagnetism in Diluted MNagnetic Semiconductors.
Hiroshi Katayama-Yoshida 1 , Kazunori Sato 1 , Tetsuya Fukushima 1 , Masayuki Toyoda 1 , Hidetoshi Kizaki 1 , An van Dinh 1 , Peter Dederichs 2
1 Condensed Matter Physics, ISIR, Osaka University , Osaka Japan, 2 Institut fur Festkoerperforschung, Forschungszentrum Juelich, Juelich Germany
Show Abstract10:30 AM - **K1.3
Electron-induced Stabilization of Ferromagnetism in Semiconductors.
Gustavo Dalpian 1
1 Centro de Ciências Naturais e Humanas, Universidade Federal do ABC, Santo Andre, SP, Brazil
Show Abstract12:00 PM - K1.5
Rashba Spin-Splitting and Spin Currents in GaN Heterojunctions
Wolfgang Weber 1 , Simon Seidl 1 , Leonid Golub 2 , Sergey Danilov 1 , Vasily Bel'kov 2 1 , Wilhelm Prettl 1 , Zee Kvon 3 , Hyun-Ick Cho 4 , Jung-Hee Lee 4
1 Department of Physics, Universität Regensburg, Regensburg Germany, 2 A.F. Ioffe Physico-Technical Institute, Russian Academy of Science, St. Petersburg Russian Federation, 3 , Institut of semiconductor physics, Novosibirsk Russian Federation, 4 , Kyungpook National University, Sankyuk-Dong Korea (the Republic of)
Show AbstractGallium nitride is a potentially interesting material system forspintronics since it is expected to become ferromagnetic with aCurie-temperature above room temperature if doped withmanganese and long spin relaxation times are detected in thismaterial. Recently we observed thatalso a substantial Rashba spin-splitting in the electron band structure is present allowing spin manipulation by an electric field [1].The Rashba spin-splitting, which is not expected in wide-band semiconductors, in GaN is caused by a large piezoelectric effect which yields a strong electric field at the AlGaN/GaN interface and a strong polarization induced doping effect.Here we report on an investigation of the circular photogalvanic effect (CPGE) caused byRashba spin-splitting [2] and on the observation of zero-bias spin separation [3] inthis material. The CPGE results in a spin polarized electric current andis caused by selective photoexcitation of carriers in k-space with circularly polarized light due to optical selection rules. Zero-bias spin separation is achieved by spin-dependent scattering of electronsdue a term in the scattering matrix elements linear in wavevector k and generates a pure spin current. Both effects have been detected in a wide range of temperaturesfrom technologically important room temperature to 4.2 K. Experiments were carried out on hexagonal (0001)-oriented GaN heterostructures applying linear or circular polarized infrared and terahertz radiation.[1] W. Weber, S.D. Ganichev, Z.D. Kvon, V.V. Bel'kov, L.E.Golub, S.N. Danilov, D. Weiss, W. Prettl, Hyun-Ick Cho, andJung-Hee Lee, Appl. Phys. Lett. 87, 262106 (2005)[2] S.D. Ganichev, and W. Prettl, Intense Terahertz Excitation of Semiconductors, Oxford University Press, (2006).[3] S.D. Ganichev, V.V. Bel'kov, S.A. Tarasenko, S.N. Danilov, S. Giglberger, Ch. Hoffmann, E.L. Ivchenko, D. Weiss, W. Wegscheider, Ch. Gerl, D. Schuh, J. Stahl, J. De Boeck, G.~Borghs, and W. Prettl,Nature Physics (London) 2, 609 (2006).
12:15 PM - K1.6
Anomalous Hall Effect Measurement in GaMnN-based Multilayered Structures.
Amr Mahrous 1 , Ahmed Emara 1 , Oliver Luen 1 , Salah Bedair 1 , John Zavada 3 , Nadia El-Masry 2
1 Dept of Electrical and Computer Engineering, North Carolina State University, Raleigh, North Carolina, United States, 3 , Army Reasearch Office, Durham, North Carolina, United States, 2 Materials Science and Engineering Department, North Carolina State University, Raleigh, North Carolina, United States
Show AbstractSince the discovery of the carrier induced ferromagnetism in transition metal doped GaAs, dilute magnetic semiconductors gathered interest because of its potential application as a new functional material utilizing the spin degree of freedom into semiconductor devices. We have reported the room temperatures ferromagnetism in MnGaN-based dilute magnetic semiconductor films. The Mn composition ranged from 0.5 to 1.5% Mn in the Ga1-xMnxN films.In this work we have studied the magnetic, optical and magneto-transport properties of the GaMnN and p-type (AlGaN/GaN) hetero-structures. Tri-layered structures of [p-type (AlGaN/GaN)/Ferromagnet-GaMnN/p-type (AlGaN/GaN)] were grown by MOCVD. The room temperature ferrommagnetic hysteresis curves of the structure rendered to be three times stronger compared to the same film grown as a bulk ferromagnetic GaMnN thin film. This finding indicates a charge transfer between the trilayers that enhances the ferromagnetism in the GaMnN film. A magnetic field dependence of the film's resistivety showed anomalous Hall Effect in the trilayer structure. This is the first step to fabricate novel functional devices that control charges and spin by using GaMnN-based ferromagnetic multilayer structures.
12:30 PM - K1.7
Mobility of Charge Carriers in Dilute Magnetic Semiconductors
Michael Foygel 1 , James Niggemann 1 , A. Petukhov 1
1 Physics, SDSMT, Rapid City, South Dakota, United States
Show AbstractWe studied electrical transport in dilute magnetic semiconductors, which is determined by scattering of free carriers by localized magnetic moments. In our calculations of the scattering time and the mobility of the majority and minority-spin carriers we took into account both the effects of thermal spin fluctuations and of built-in spatial disorder of the magnetic atoms. These effects are responsible for the magnetic-field dependence of the mobility of the charge carriers. The application of the external magnetic field suppresses the thermodynamic spin fluctuations thus increasing the mobility. Simultaneously, depending on the type of the carriers and on parameters of the impurity potential, scattering by built-in spatial fluctuations of the atomic spins increases or decreases with the magnetic field. The latter effect is due to the change in the magnitude of the random local Zeeman splitting with the magnetic field. We discuss the role of the above effects on mobility and magnetoresistance of semiconductors where magnetic impurities are electrically active or neutral.
12:45 PM - K1.8
Electronic Transport in Diluted Magnetic Semiconductors: Application of the Memory Function Formalism for Spin and Charge Disordered Media.
Fedir Kyrychenko 1 , Carsten Ullrich 1
1 Department of Physics, University of Missouri - Columbia, Columbia, Missouri, United States
Show AbstractK2: Nitride DMS
Session Chairs
Tuesday PM, April 10, 2007
Room 3009 (Moscone West)
2:30 PM - **K2.1
Development of Ferromagnetic III-N Semiconductor Materials for Spintronic Applications.
Nate Newman 1 , H. Liu 1 , S. Wu 1 , R. Singh 1 , J. Medvedeva 2 , Z. Yu 3 , S. Krishnamurthy 3 , A. Freeman 4 , M. van Schilfgaarde 1
1 School of Materials, Arizona State University, Tempe, Arizona, United States, 2 Physics Department, University of Missouri-Rolla, Rolla, Missouri, United States, 3 , SRI International, Menlo Park, California, United States, 4 Physics Department, Northwestern University, Evanston, Illinois, United States
Show AbstractRecent progress towards producing prototype magnetoelectronic structures based on III-N semiconductor materials will be described. This talk will specifically focus on III-N materials’ properties associated with producing, injecting, transporting, manipulating and detecting spin-polarized electron populations. MBE growth has been used to synthesize single phase and epitaxial Cr-doped GaN and AlN thin films that exhibits ferromagnetism to temperatures above 900K. Channeling RBS studies on optimized GaN films show that ~90% of the Cr impurities occupy substitutional sites (CrGa) and as much as 60% are magnetically active. This unambiguously demonstrates that Cr-doped III-Nitrides are true dilute magnetic semiconductors. Additional theoretical and experimental work has shown that ferromagnetism in III-N semiconductors arises as a result of a double exchange like mechanism where carriers move in the Cr t2 near mid-gap level. The electrical resistivity of magnetic Cr-doped GaN films are found to follow the exponential law, R=Roexp[(Tο/T)1/2], indicating that variable range hopping in the Cr t2 defect level is indeed the dominant transport mechanism. We will also describe other advantages of the III-N semiconductor system for spintronic applications. Numerical calculations predict two orders of- magnitude longer electron spin relaxation times in GaN than in GaAs. First-principles theoretical calculations reveal the possibility of efficient spin injection from a ferromagnetic Cr-doped GaN electrode through an AlN tunnel barrier. Progress in developing magnetic tunnel junctions using Cr-doped GaN electrodes will be discussed. We have also used an antiferromagnetic MnO overlayer to demonstrate exchange biasing of Cr-doped GaN films. This review should provide some insight into the potential for realizing new and exciting possibilities in the area of spintronics. The work at ASU supported by the DARPA spins program and the work at NU supported by the NSF (through its MRSEC program).
3:00 PM - K2.2
Properties of MOVPE Grown (Ga,Cr)N Layers for Spintronic Applications.
Nicoleta Kaluza 1 , Yong Cho 1 , Hilde Hardtdegen 1 , Vitaliy Guzenko 1 , Thomas Schaepers 1 , Uwe Breuer 2 , Klaus Schmalbuch 3 , Bernd Beschoten 3 , Jan Zenneck 4 , G. Chambard 5 , Pierre Ruterana 5
1 Institute of Bio- and Nanosystems (IBN-1),Center of Nanoelectronic Systems for Information Technology (CNI), Virtual Institute of Spin Electronics (VISel), Research Center Juelich, Germany, Juelich Germany, 2 Central Division of Analytical Chemistry (ZCH), Research Center Juelich, Juelich Germany, 3 II. Physikalisches Institut and VISel , RWTH Aachen, Aachen Germany, 4 IV. Physikalisches Institut and VISel, Georg-August Universität Göttingen , Göttingen Germany, 5 SIFCOM UMR 6176, CNRS-ENSICAEN , Caen France
Show Abstract3:15 PM - K2.3
Relation between Structural, Electronic, and Magnetic Properties in MOCVD Grown (Ga,Fe)N.
Alberta Bonanni 1 , Michal Kiecana 2 , Clemens Simbrunner 1 , Hanka Przybylinska 2 , Andrea Navarro-Quezada 1 , Matthias Wegscheider 1 , Maciej Sawicki 2
1 Institute for Semiconductor and Solid State Physics, Johannes Kepler University, Linz Austria, 2 Institute of Physics, Polish Academy of Sciences, Warsaw Poland
Show Abstract3:30 PM - K2.4
Surface Diffusion Effects on the Magnetic Properties on MOCVD-grown GaMnN and GaFeN
Matthew Kane 1 2 , Shalini Gupta 2 , William Fenwick 2 , Eun Park 2 , Man Han 4 , Z. Zhang 4 , Enno Malguth 3 , Axel Hoffmann 3 , Ian Ferguson 2 1
1 Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 2 Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 4 Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia, United States, 3 Institut für Festkörperphysik, Technische Universität Berlin, Berlin Germany
Show AbstractThough wide bandgap dilute magnetic semiconductors have been investigated for room temperature spintronic applications, their materials properties and ultimate device utility are still a subject of controversy. Initial theories predicted room temperature hole mediated ferromagnetism in the system [1]; such ferromagnetic behavior is often reported in the literature. Because Mn has a very strong interaction self-interaction parameter in GaN, it has been suggestest that spinodal decomposition into Mn-rich regions is responsible for the observed magnetic behavior [2]. It has also been recently predicted that the magnetic phase segregation can be altered by tailoring the charge state of the Mn [3]. Ultimately, it will be essential to correlate the nanoscale distribution of elements as a result of the processing conditions of the growth technique used. In this work, we explore the magnetic properties of GaMnN and GaFeN grown by metalorganic chemical vapor deposition as a function of growth conditions including the use of silane as an antisurfactant to modify the adatom surface diffusion length and to modify the charge state of transition metal ions during growth. Magnetic hysteresis is observed at room temperature in the samples, even at dilute alloying concentrations. Three contributions may exist in the overall measured magnetization – a Pauli paramagnetic contribution from the d5 ions (Mn2+/Fe3+), a temperature independent Van Vleck paramagnetic contribution from the d4/d6 (Mn3+/Fe2+) ions, and an above room-temperature ferromagnetic contribution from some unidentified Mn-rich phase. Conversion of the trivalent to divalent transition metal states has been confirmed via optical transmission techniques. With increasing silicon codoping, a distinct splitting is observed in the zero field cooled and field cooled magnetization curves. This is consistent with an observed magnetic hysteresis due to an agglomeration of nanoscale magnetic regions with high blocking temperatures due to large anisotropies inherent in the layer-by-layer growth. With Si doping, the anti-surfactant effect from the Si results in a decrease in surface diffusion length and thus Mn-rich island size, leading to the observed blocking behavior. These results from a nominally charged surfactant species will be compared with those from neutral surfactants and growth rate effects to discuss the effects two-dimensional surface diffusion during the growth process on the magnetic behavior in the Ga1 xMnxN system. Control of the magnetization strength due to Mn-Mn interactions during the MOCVD process is a complex function of the gas flow rates, temperature, growth rate, surface diffusion length and Mn-charge state during MOCVD growth.[1] T. Dietl, H. Ohno, et al., Science 287 (2000) 1019.[2] K. Sato, H. Katayama-Yoshida, et al., Jap. Journ. Appl. Phys. 44 (2005) 948.[3] T. Dietl, Nat. Mat. 9 (2006) 673.
4:30 PM - **K2.6
Rare Earth Doped III-Nitrides for Optoelectronics and Spintronics
John Zavada 1
1 , U. S. Army Research Office, Raleigh, North Carolina, United States
Show AbstractIn recent years, red, blue, green, and infrared luminescence has been achieved in electronic devices based on rare earth (RE) doped III-N films. Potential applications for these devices include full-color displays, white lighting systems, and electrically-activated optical amplifiers. These materials may also have an impact in spintronics since experiments have shown that III-N thin films, doped at low RE concentrations, give rise to room temperature ferromagnetism. Here we will review latest spectroscopic and magnetic data of III-N thin films doped with different RE ions. Samples have been prepared by different methods including ion-implantation, metal organic molecular beam epitaxy, and molecular beam epitaxy. While luminescence and ferromagnetic behavior depend strongly upon the synthesis method, results indicate that magnetic and optical functionality can be achieved on a single chip.
5:00 PM - **K2.7
Gd-doped GaN – A ferromagnetic semiconductor with high Curie temperature and unusual magnetic properties
Klaus Ploog 1
1 , Paul Drude Institute for Solid State Electronics, Berlin Germany
Show AbstractFerromagnetic semiconductors are considered to be efficient spin injectors for spintronic devices and they allow the realization of all-semiconductor devices, including spin valves and GMR devices. Despite more than four decades of research, there are only very few ferromagnetic semiconductors with Curie temperature above room temperature. We have recently reported room temperature ferromagnetism in Gd-doped GaN. In addition to the high Curie temperature of 800 K, magnetic measurements reveal an unexpectedly high magnetic moment per Gd atom. This colossal magnetic moment was also observed in GaN implanted with Gd. The observed ferromagnetic behavior cannot be explained by the classical theories of ferromagnetism. We have therefore introduced a phenomenological model assuming a large polarization of the GaN matrix by the Gd atoms. In addition to the colossal magnetic moment, Gd-doped GaN exhibits a magnetic behavior very different from classical ferromagnets. Details will be presented in this contribution.
5:30 PM - K2.8
Effect of Radiation on Nitride Dilute Magnetic Semiconductors.
Jennifer Hite 1 , K. Allums 1 , R. Davies 1 , R. Frazier 1 2 , G. Thaler 1 3 , C. Abernathy 1 , S. Pearton 1 , R. Dwivedi 4 , S. Ardalan 4 , R. Wilkins 4
1 , University of Florida, Gainesville, Florida, United States, 2 , Naval Research Laboratory, Washington, District of Columbia, United States, 3 , Sandia National Laboratory, Alburquerque, New Mexico, United States, 4 , Prairie View A&M University, Prairie View, Texas, United States
Show AbstractInterest in the III-nitrides has recently been extended to applications in two extreme arenas: space and spintronics. The ability of these materials, especially GaN, to operate under high temperatures and power loads also extends to the radiation laden conditions seen in space. Of the types of radiation experienced in low earth orbits, the most prevalent is proton bombardment. In addition, the field of spintronics has embraced the use of GaN as a matrix for dilute magnetic semiconductors (DMS) which may provide a path to devices such as magnetic tunnel junctions, spin valves, and spin-FETs. As work progresses in this field, it is also important to investigate the effects radiation have on DMS materials semiconductors, which might also aid understanding of the mechanism involved in the magnetic ordering of these materials. Both GaGdN and GaCrN films were grown via gas source molecular beam epitaxy and exposed to high energy proton irradiation. The dosages chosen (10 and 40 MeV at 5 x 10^9 cm^-2) were to simulate the radiation incurred by space craft in low earth orbits for 10 years. With these conditions, the stopping distance of the protons is expected to be much greater than the DMS film thicknesses. Photoluminescence measurements of the DMSs were comparable to that of undoped GaN, with the band edge emission decreasing with radiation. Magnetic measurements also showed decreasing signal with radiation. In both DMS films, the GaGdN experienced a much larger response to radiation than GaCrN, with a 87% loss of saturation magnetization at higher proton energy. Annealing the irradiated DMS samples under a nitrogen plasma at 500C resulted in complete magnetic recovery. The greater sensitivity of the Gd-doped material is expected due to the lower dopant concentration as compared to the films using a Cr dopant.
5:45 PM - K2.9
Metastable Magnetic Properties of Gd-doped GaN.
Andreas Ney 1 , L. Perez 2 , K H Ploog 2 , F. Wilhem 3 , A. Rogalev 3 , T. Kammermeier 1 , E. Manuel 1 , V. Ney 1 , S. Dhar 1 2
1 Experimentalphysik, Universitaet Duisburg-Essen, Duisburg Germany, 2 , Paul-Drude-Institut , Berlin Germany, 3 , European Synchrotron Radiation Facility (ESRF), Grenoble France
Show Abstract
Symposium Organizers
Cammy R. Abernathy University of Florida
Salah Bedair North Carolina State University
Pierre Ruterana SIFCOM-ENSICAEN
Rachel Frazier Naval Research Laboratory
K3: Oxide DMS
Session Chairs
Wednesday AM, April 11, 2007
Room 3009 (Moscone West)
9:30 AM - K3.1
Room-temperature Ferromagnetism in GaN and ZnO Powders.
Peter Moeck 1 , Lori Noice 1 , Bjoern Seipel 1 , Chunfei Li 1 , Rolf Erni 2 , Amita Gupta 1 3 , Nigel Browning 2 , Frank Owens 4 , Venkat K Rao 3
1 Department of Physics, Portland State University, Portland, Oregon, United States, 2 Department of Chemical Engineering and Materials Science, University of California at Davis, Davis, California, United States, 3 Department of Materials Science, The Royal Institute of Technology, Stockholm Sweden, 4 Department of Physics, Hunter College, New York, New York, United States
Show Abstract9:45 AM - K3.2
Magnetic and Electronic Properties of n type (Al,Ga) co-doped Zn(Cu)O based Dilute Magnetic Semiconductors.
Deepayan Chakraborti 1 , John Prater 2 , Jagdish Narayan 1
1 Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina, United States, 2 Marerials Sciences Division, Army Research Office, Research Triangle Park, North Carolina, United States
Show Abstract10:00 AM - K3.3
Room Temperature Ferromagnetism in Carbon-doped ZnO
Hui Pan 1 , Jiabao Yi 2 , Jianyi Lin 1 3 , Yuan Ping Feng 1 , Jun Ding 2 , Li Hui Van 2 , Jianhua Yin 2
1 Department of Physics, National University of Singapore, Singapore Singapore, 2 Department of Materials Science & Engineering, National University of Singapore, Singapore Singapore, 3 , Institute of Chemical & Engineering Sciences, Singapore Singapore
Show AbstractWe report magnetism in carbon doped ZnO. Our first-principles calculations based on density functional theory predicted that carbon substitution for oxygen in ZnO results in a magnetic moment of 1.78 μB per carbon. The theoretical prediction was confirmed experimentally. C-doped ZnO films deposited by pulsed laser deposition with various carbon concentrations showed ferromagnetism with Curie temperatures higher than 400 K, and the measured magnetic moment based on the content of carbide in the films (1.5 - 3.0 μB per carbon) is in agreement with the theoretical prediction. The magnetism is due to bonding coupling between Zn ions and doped C atoms. Results of magneto-resistance and abnormal Hall effect show that the doped films are n-type semiconductors with intrinsic ferromagnetism. The carbon doped ZnO could be a promising room temperature dilute magnetic semiconductor (DMS) and our work demonstrates possiblity of produing DMS with non-metal doping.
10:15 AM - **K3.4
Transition Metal Doped ZnO for Spintronics
D. Norton 1 , M. Ivill 1 , A. Hebard 2 , J. Zavada 3 , W. Chen 4 , I. Buyanova 4 , Stephen Pearton 1
1 MSE, Univ.Florida, Gainesville, Florida, United States, 2 Physics, University of Florida, Gainesville, Florida, United States, 3 Electronics Division, US Army Research Office, Research Triangle Park, North Carolina, United States, 4 Physics and Measurement Technology, Linkoping University, Linkoping Sweden
Show AbstractSpin-dependent phenomena in ZnO may lead to devices with new or enhanced functionality, such as polarized solid-state light sources and sensitive biological and chemical sensors. In this talk we review experimental results on transition metal doping of ZnO and show that the material can be made with single phase at high levels of Co incorporation(~15 at %) and exhibits the Anomalous Hall Effect (AHE). ZnO is expected to be one of the most promising materials for room temperature polarized light emission, but to date we have been unable to detect optical spin polarization in ZnO. The short spin-relaxation time observed likely results from the Rashba effect. Possible solutions involve either cubic phase ZnO or use of additional stressor layers to create a larger spin-splitting in order to get polarized light emission from these structures or to look at alternative semiconductors and fresh device approaches.
10:45 AM - K3.5
Comparison of Structural and Magnetic Properties of Co- and Gd-Doped ZnO and Gd-Doped GaN.
Verena Ney 1 , F.-Yuh Lo 2 , A. Melnikov 2 , A. Wieck 2 , T. Kammermeier 1 , S. Dhar 1 3 , A. Ney 1
1 Experimentalphysik, Universitaet Duisburg-Essen, Duisburg Germany, 2 Angewandte Festkoerperphysik, Ruhr Universitaet Bochum, Bochum Germany, 3 , Paul-Drude-Institut fuer Festkoerperelektronik, Berlin Germany
Show AbstractIt has been found recently, that ion implanted dilute magnetic semiconductors (DMS) like Gd:GaN can exhibit long range magnetic order above room temperature together with a colossal magnetic moment per doping atom in the very dilute limit [1]. ZnO with its favorable optical properties is another wide band-gap DMS which shows magnetic order up to room temperature [2]. Here we performed structural and magnetic investigations on ZnO single crystals which were ion implanted with different concentrations of Co and Gd and on cubic and wurtzite MBE grown GaN which were ion implanted with Gd. The samples were thouroughly characterized prior to the implantation by means of X-ray diffraction and electron spin resonance. Phase segregation is ruled out based on X-ray diffraction, however, at high implantation doses indications for structural damage are visible. All samples show magnetic order at room temperature as revealed by SQUID measurements. However, there are significant differences in the magnetic properties between wurtzite and cubic GaN and wurtzite ZnO with Gd-implantation on the one hand and between Gd and Co implantation of ZnO on the other hand. The influence of the defects on the magnetic properties will be discussed by means of annealing experiments. [1] S. Dhar et al., Appl. Phys. Lett. 89, 062503 (2006).[2] M. Venkatesan et al., Phys. Rev. Lett. 93, 177206 (2004).
11:30 AM - K3.6
The Effects of Rapid Thermal Annealing on the Magnetism in Co-doped ZnO Nanocrystals.
Xuefeng Wang 1 , J. Xu 1 , Jin An 1 , W. Cheung 1 , Ning Ke 1 , S. Wong 1
1 Department of Electronic Engineering, The Chinese University of Hong Kong, Shatin, New Territories Hong Kong
Show Abstract11:45 AM - K3.7
Effects of Defects and Thermal Annealing on the Ferromagnetism of (Zn,Co)O Nanowires.
Ji-Jung Kai 1 , Jong-Yi Wu 1 , Fu-Rong Chen 1
1 Department of Engineering and System Science, National Tsing Hua University, Hsinchu Taiwan
Show Abstract12:00 PM - K3.8
Structural, Magnetic and Transport Properties of Cobalt doped ZnO Epitaxial Thin Films
Yoon Jeong 1 , Hyojin Lee 1 , Sung-Ho Lee 1
1 Physics, POSTECH, Pohang Korea (the Republic of)
Show AbstractSemiconductors with ferromagnetism at room temperature has been actively searched for in recent years; a prospect of spintronic devices using both charge and spin continuously gives impetus to the activities. Since Mn-doped GaAs, perhaps the representative magnetic semiconductor, possesses the Curie point Tc well below room temperature, transition metal doped oxide materials have been of particular interest as a high Tc material. Co substituted ZnO, for example, is one of the prime candidates. However, various studies of Co-doped ZnO thin films do not seem to converge on a definite picture and controversy continues. What is needed is well synthesized and thoroughly characterized samples. A series of Zn1-xCoxO (0≤x≤0.2) thin films on sapphire (0001) substrates were epitaxially grown by using Laser MBE deposition technique, controlling laser fluence, substrate temperatures and oxygen partial pressures. In-situ RHEED pattern showed that the films grew in the layer by layer growth mode. We performed high resolution XRD, SEM, TEM, and AFM measurements to confirm the structure and morphology of the films. XRD figures showed that the films were of single phase with the pure ZnO wurtzite structure. AFM measurements showed that the RMS values of roughness of the films were about 2Å. XAS and XMCD measurements using synchrotron radiation were also carried out to confirm the microscopic origin of magnetism. We paid particular attention to the role of oxygen vacancies. Oxygen diffusion rate into the films by post-deposition treatments were carefully studied as a function of thickness. Magnetization, resistivity, and Hall coefficient measurements were also carried out systematically as a function of x and oxygen contents. These measurements revealed that Co doping brings about self-curing of oxygen vacancies. At x = 0.15, the films become good insulators which then can be further doped with carriers. Strong correlation between the presence of the n-type carriers and the emergence of magnetism at room temperature was found. These results will be presented in detail.
12:15 PM - K3.9
Effect of Free Carrier on Ferromagnetic Properties of Zn1-xCoxO Thin Films.
Kousik Samanta 1 , Pijush Bhattacharya 1 , Ram Katiyar 1 , J. Duque 2 , C. Rettori 2 , P. Pagliuso 2
1 Physics, University of Puerto Rico, San Juan, Puerto Rico, United States, 2 Instituto de Fisica DEQ-UNICAMP, Cidade Universitaria- Barao, SP Belize
Show AbstractK4: Mn-Containing DMS
Session Chairs
Wednesday PM, April 11, 2007
Room 3009 (Moscone West)
2:30 PM - **K4.1
Strategies and Challenges for Achieving Room-Temperature Ferromagnetism in III-Mn-V Alloys.
Jacek Furdyna 1
1 Physics, University of Notre Dame, Notre Dame, Indiana, United States
Show AbstractWhile ferromagnetic III1-xMnxV alloys such as Ga1-xMnxAs exhibit features that are attractive for spin-electronic (“spintronic”) applications, ferromagnetism in these systems typically occurs below 200K, which severely limits their practical usefulness. It is now well established that the Curie temperature TC in these materials increases with increasing concentration of Mn ions x occupying substitutional group-III positions (MnIII), and with the concentration of holes p. We have shown that during typical growth of III1-xMnxV alloys by low-temperature molecular beam epitaxy (LT-MBE) nature imposes a thermodynamic limit on both these parameters. First, there is a limit on the Fermi level (i.e., on the value of p) which can form during the growth process; and since MnIII ions act as acceptors, this automatically also limits the value of x. When xmax is attained, any additional Mn ions are forced to interstitial positions, where they act as donors, thus reducing the effective hole concentration; and they also compensate the magnetic moments of MnIII by antiferromagnetic pairing. This automatically reduces TC as well as the total magnetization of the III1-xMnxV system. While the above processes arise as a consequence of growth thermodynamics, having a clear understanding of what limits TC allows us to design strategies to circumvent these bottlenecks. For example, the concentration of Mn interstitials can be markedly reduced by annealing at special conditions, thus increasing both TC and the total magnetic moment of the system. One can also base modulation-doping strategies (including, counter-intuitively, co-doping by donors), which can be designed to increase TC beyond these thermodynamically-imposed limits. We will discuss a series of such approaches designed for the case of Ga1-xMnxAs. One should note that the limits identified above all arise from the formation and behavior of defects. We can thus make a general statement that the key to increasing TC in III1-xMnxV alloys lies in our ability to control and to manipulate defects in these materials in a desired manner.
3:00 PM - **K4.2
Ferromagnetic GaMnN Films and Heterostructures (a Review).
Nadia El-Masry 1
1 Materials Scienec and Engineering Department, North Carolina Satate University, Raleigh, North Carolina, United States
Show Abstract3:30 PM - **K4.3
Spin Carrier Exchange Interactions in Wide Bandgap Diluted Magnetic Semiconductors GaMnN and ZnMnO.
Henri Mariette 1 , Wojciech Pacuski 1 2 , David Ferrand 1 , Eirini Sarigiannidou 1 , Joel Cibert 3 , Piotr Kossacki 2 , Jan Gaj 2
1 DRFMC, CEA-CNRS, Grenoble France, 2 Institute of Experimental Physics, Warsaw university, Warsaw Poland, 3 Lab Louis Néel, CNRS, Grenoble France
Show Abstract4:45 PM - K4.5
Charge Transfer Through a Hetero-Interface and its Effect on the Ferromagnetic Properties of GaMnN
Erdem Arkun 2 , Acar Berkman 2 , Mason Reed 1 , John Zavada 3 , Nadia El-Masry 2 , Salah Bedair 1
2 Materials Science and Engineering Department, Carolina State Univresity, Raleigh, North Carolina, United States, 1 Dept of Electrical and Computer Engineering, North Carolina State University, Raleigh, North Carolina, United States, 3 , Army research Office, Durham, North Carolina, United States
Show AbstractThe study demonstrates that a ferromagnetic or paramagnetic GaMnN film can be rendered paramagnetic or stronger ferromagnetic by changing the occupancy of the Mn energy band.To check this assumption, the effect of presence of a silicon doped GaN layer adjacent to a GaMnN layer was investigated. The starting GaMnN layer (paramagnetic) was grown between GaN:Si layers to form a GaN:Si/GaMnN/GaN:Si (DHS), and was found to stay paramagnetic. In another case study an initially ferromagnetic GaMnN layer was selected as a starting material, and was grown between two silicon doped GaN layers. Carriers in the n-type GaN layer will transfer to the adjacent GaMnN layer, in which the Mn 3d-band is partially occupied, and fill up the Mn band. Since carriers are not mobile with the Mn 3d band completely occupied, ferromagnetic properties were effectively reduced or disappeared depending on the doping level of the adjacent GaN:Si layer. According to our model, we will also show that initially non-magnetic GaMnN can be rendered ferromagnetic by placing an Mg-doped GaMnN layer adjacent to it. These experiments explicitly show that the ferromagnetic properties are carrier mediated and perturbations to the electronic structure of the crystal alter the magnetic properties. The Mn concentration in all of the films was 1020atoms/cm3 as measured by SIMS. GaMnN films were grown at a temperature, with growth parameters, that is either leading to ferromagnetic or paramagnetic GaMnN films as desired. These films showed ferromagnetism with a magnetization magnitude depending on the availability of Mg acceptor levels, and in turn dependent on the thickness of the GaN:Mg layer.
5:00 PM - K4.6
Compositional Tuning of Ferromagnetism in Ga1-xMnxP and Ga1-xMnxP-based Quaternary Alloys
Peter Stone 1 2 , Michael Scarpulla 1 2 , Rouin Farshchi 1 2 , Ian Sharp 1 2 , Kin Yu 2 , Jeff Beeman 2 , Elke Arenholz 3 , Eugene Haller 1 2 , Oscar Dubon 1 2
1 Materials Science and Engineering, University of California-Berkeley, Berkeley, California, United States, 2 Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 3 Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractThat the Curie temperature (TC) record in Ga1-xMnxAs has remained well below room temperature suggests the need to look to other semiconductors to achieve the goal of room temperature ferromagnetism. A natural consequence has been an increased interest in wider-gap Ga-Mn-Group V materials in which smaller lattice constants and enhanced p-d exchange may lead to stronger inter-Mn interactions. In fact, above room temperature ferromagnetism has been reported in the (Ga,Mn)N and (Ga,Mn)P systems [Thaler et al. Appl. Phys. Lett. 80 3964 (2002); Theodoropoulou et al. Phys. Rev. Lett. 89 107203 (2002)]. In this work we report compositional tuning of the ferromagnetic properties of the carrier-mediated phase of Ga1-xMnxP produced by Ion Implantation followed by Pulsed-Laser Melting (II-PLM). We find that TC increases monotonically with the substitutional Mn concentration x for 0.009≤x≤0.042 with TC varying from 6 K to 65 K over this range of x [Farshchi et al. Solid State Commun. 140 443 (2006)]. Extrapolation of this linear trend indicates that x ≈ 0.18 may be required for room temperature ferromagnetism in Ga1-xMnxP. While TC is lower in Ga1-xMnxP relative to Ga1-xMnxAs for all x, the TC vs. x trend is similar in the two materials. This is consistent with results obtained by X-ray magnetic circular dichroism (XMCD) measured at the Mn L3,2 edge in which nearly identical XMCD lineshapes are observed in the two materials [Stone et al. Appl. Phys. Lett. 89 012504 (2006); Edmonds et al., Appl. Phys. Lett. 84 4065 (2004)]. This indicates that the electronic environment around substitutional Mn is quite similar in Ga1-xMnxP and Ga1-xMnxAs despite differences in bond lengths, acceptor binding energies, and hole localization associated with the anion substitution.In the Ga1-xMnxP1-ySy system both the spin polarization of the hole states and bulk magnetic properties of Ga1-xMnxP are strongly influenced by compensation of ferromagnetism-mediating holes due to electrons introduced by sulfur donors. Both the TC and XMCD in Ga1-xMnxP1-ySy decrease monotonically with y. Finally, we explore Ga1-xMnxAs1-yPy for which it has been predicted [Masek et al. cond-mat/0609158v1] that TC will increase in these systems as y increases, and, thus, provide a route to room temperature ferromagnetism based on the well-studied Ga1-xMnxAs system. This work is supported by the Director, Office of Science, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. The Advanced Light Source is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under contract No. DE-AC02-05CH11231.
5:15 PM - K4.7
Hydrogen Passivation Patterning of Ferromagnetic Semiconductors for Planar Spintronics
Rouin Farshchi 1 3 , Rajesh Chopdekar 1 , Yuri Suzuki 1 , Paul Ashby 3 , Ian Sharp 1 3 , Jeffrey Beeman 3 , Eugene Haller 1 3 , David Hwang 2 , Costas Grigoropoulos 2 , Daniel Estrada 1 3 , Oscar Dubon 1 3
1 MSE, UC Berkeley, Berkeley, California, United States, 3 , Lawrence Berkeley Lab, Berkeley, California, United States, 2 ME, UC Berkeley, Berkeley, California, United States
Show AbstractFerromagnetic semiconductors demonstrate a unique correlation of magnetic and electrical properties that make them promising candidates for use in spin-based electronics, or spintronics. These materials are typically based on III-V or II-VI semiconductors in which a small fraction of the cation sublattice host atoms is substituted with a magnetic impurity such as Mn, Cr or Co. We have recently demonstrated that Mn ion implantation followed by pulsed laser melting (II-PLM) is an effective processing route for creating ferromagnetic III-Mn-V semiconductors. By this process Ga1-xMnxAs films displaying magnetic and electrical properties similar to those of films formed by low-temperature molecular beam epitaxy (LT-MBE) have been synthesized.Here we demonstrate the application of II-PLM and hydrogenation to produce planar Ga1-xMnxAs regions embedded in a non-magnetic GaAs substrate. Gallium manganese arsenide prepared by II-PLM is exposed to a hydrogen plasma. Such hydrogenation has the well-known effect of passivating the Mn acceptors, rendering them electrically and magnetically inactive. By blocking the desired active regions of Ga1-xMnxAs with a lithographically patterned oxide layer during hydrogenation, one forms isolated active regions in a passivated substrate. Conductance atomic force microscopy (C-AFM) reveals the electrical (hence magnetic) passivation of the plasma exposed regions while magnetotransport measurements performed on hydrogenation-patterned Hall bar samples show that the oxide-protected regions are unaffected by the hydrogenation. By this process arbitrarily shaped microscopic structures can be formed. To achieve sub-micrometer resolution, we propose a maskless process based on focused laser radiation to locally anneal hydrogenated films. Manganese-hydrogen complexes in Ga1-xMnxAs are stable to approximately 190C; using focused laser radiation, one can locally break up Mn-H complexes and thus reactivate Ga1-xMnxAs regions in a passivated substrate. Because the laser spot-size can be focused to sub-50nm by optical near-field schemes, this technique allows for the realization of nanoscale dot and wire structures from hydrogenated Ga1-xMnxAs. Although Ga1-xMnxAs is used as the test bed for hydrogenation patterning, these techniques can be applied to other ferromagnetic semiconductors in which hydrogen has a passivating effect on dopants including transition metal impurities.This work was supported in part by the U.S. Department of Energy under contract No. DE-AC02-05CH11231. O.D.D. acknowledges support from the National Science Foundation under contract number DMR-0349257.
5:30 PM - K4.8
Magnetic Properties of Mn Substituted I-III-VI2 Semiconductors
Susan Schorr 1 , Roland Hoehne 2 , Boris Korzun 3
1 Solar Energy Research (SE3), Hahn-Meitner-Institute Berlin, Berlin Germany, 2 Institute of Experimental Physics II, University Leipzig, Leipzig Germany, 3 Institute of Physics of Solids and Semiconductors, National Academy of Science Belarus, Minsk Belarus
Show AbstractTernary AIBIIIX2VI semiconductors were proposed as new class of ferromagnetic semiconductors [1]. Ab initio calculations showed [2] the favoritism of the ferromagnetic state. Predicted Curie temperatures are 100-160 K [2,3] (CuGaX2 (X=S,Se) with Mn on Ga-site), calculations on CuAl1-xMnxS2 estimated TCs which are 10% higher. More recently first-principles calculations [4] evaluated the magnetic stability energy ΔEFM=EFM-EAFM for different Mn pair configuration showing ΔEFM<0 when Mn substitutes either the Cu or BIII site in CuBIIIS2. For a MnCu-MnB pair ΔEFM=0, i. e. no ferromagnetism would occur. Up to now besides theoretical calculations only a few experimental results concerning I-III-VI2 chalcopyrites with Mn substitution exist in literature, reporting paramagnetic behaviour, antiferromagnetic coupling or the absence of magnetic order.In the presented work the first experimental evidence for ferromagnetism in Mn substituted I-III-VI2 semiconductors is discussed. Powder samples of CuMn2xIn1-xS2, Mn2xCu1-xInS2 and Mn2xCu1-xAlS2 were investigated by X-ray diffraction and magnetization measurements using a SQUID. The results of the Rietveld analysis of the diffraction data showed, that Mn occupies cation sites of the chalcopyrit type structure. Moreover no hints for the existence of Mn precipitates or other Mn alloys as well as Mn oxides can be found.The field depenedence of the mass magnetization for Mn2xCu1-xInS2 and Mn2xCu1-xAlS2 is characterized by a dominating linear behaviour with a positive and strongly temperature dependent susceptibility as expected for paramagnets. After subtraction of the linear part of the magnetization s-formed, ferromagnetic like loops with almost no hysteresis and almost no temperature dependence between 2 and 300 K were obtained. This behaviour speaks for a real effect of ferromagnetism stable well above 300 K. In the case Mn substitutes the BIII site (CuMn2xIn1-xS2), ferromagnetic like hysteresis was observed below 15K. However, this effect is small in comparison to the paramagnetic part of magnetization.The temperature dependence of the magnetization at different magnetic fields shows a pronounced splitting between ZFC and FC curves below certain temperatures (15K for Cu1.04Mn0.05In0.91S2 and 50 K for Mn0.06Cu0.90In1.04S2), indicating the existence of a magnetic exchange interaction. It should be noted, that in the case of MnCu-MnB substitution only paramagnetic behaviour with no indication of a magnetic transition was observed.In agreement with theory [4] it was shown experimentally for the first time, that Mn substitution on either the Cu or the BIII site in I-III-VI2 chalcopyrites leads to ferromagnetic behaviour.[1] Zhao et al., J Magn Magn Mat 246 (2002) [2] Picozzi et al., Phys Rev B 66 (2002) [3] Wimmer et al., Phys Rev B 24 (1981) Jansen et al., Phys Rev B 30 (1984) [4] Zhao et al., Phys Rev B 69 (2004)
K5: Poster Session: DMS
Session Chairs
Thursday AM, April 12, 2007
Salon Level (Marriott)
9:00 PM - K5.1
Materials Design of CuAlO2-based Dilute Magnetic Semiconductors for Semiconductor Spintronics
Hidetoshi Kizaki 1
1 , The Institute of Scientific and Industrial Resarch, Osaka University, Osaka Japan
Show AbstractCuAlO2 is a transparent semiconductor and has direct band gap of 3.5 eV and indirect gap of 1.8 eV. Recently, CuAlO2 attracts much attention as a candidate of p-type transparent conducting oxide. Moreover, due to its characteristic electronic structure CuAlO2 is a promising compound for effective thermoelectric materials. In this paper, we explore another potentiality of CuAlO2 and we propose a first-principles materials design of ferromagnetic dilute magnetic semiconductors (DMS) based on CuAlO2 for semiconductor spintronics [1]. First, in order to obtain overall chemical trend of magnetic states of CuAlO2-DMS, we calculate total energy difference between ferromagnetic state and paramagnetic state of (Cu, TM)AlO2, where TM=V, Cr, Mn, Fe, Co and Ni. This energy difference gives an estimation of Curie temperature within the mean field approximation [2]. Substitutional and magnetic disorder in (Cu, TM)AlO2 is treated by using the Korringa-Kohn-Rostoker coherent potential approximation (KKR-CPA) method [3]. All of the present calculations are based on the local density approximation. It is found that all of TM impurities show high-spin magnetic states and the ferromagnetic state is stable in Mn-, Fe, Co- and Ni-doped CuAlO2. Calculated electronic structure of them shows clear impurity band in the band gap and this means that the ferromagnetism is stabilized due to the double exchange mechanism[2]. All of ferromagnetic (Cu, TM)AlO2-DMS show half-metallic density of states. Next, to estimate Curie temperature of CuAlO2-DMS, we calculate effective exchange interactions between magnetic impurities in CuAlO2-DMS by using the Liechtenstein’s formula [4]. In this formula, the total energy change due to infinitesimal rotations of the two magnetic moments embedded in CuAlO2-DMS at sites i and j is calculated using the magnetic force theorem and the total energy change is mapped on the classical Heisenberg model to estimate the effective exchange interaction Jij. It is found that exchange interactions in CuAlO2-DMS are in general short ranged, because the magnetic interaction is mediated by deep impurity bands (double exchange). In addition, it is found that in-plane exchange interactions in CuAlO2-DMS are ferromagnetic, on the other hand, interlayer exchange interactions are very weak. We will show exact Curie temperatures of the CuAlO2-DMS estimated by the Monte Carlo simulation for the Heisenberg model with ab-initio exchange interaction.1. H. Kizaki et al., Jpn. J. Appl. Phys. 44, L1187 (2005).2. H. Akai and P. H. Dederichs, Phys. Rev. B 47, 8739 (1993).3. K. Sato et al., Europhysics Lett. 61, 403 (2003).4. A. I. Liechtenstein et al., J. Magn. Magn., Mat. 67, 65 (1987).
9:00 PM - K5.2
Effects of the Annealing Temperature and Dose on a Ferromagnetic Property of Cu Implanted GaN.
Jong-Han Lee 1 3 , Sangwon Shin 2 3 , Sunggoo Lee 2 3 , In-Hoon Choi 1 , Chungnam Whang 2 , J. Lee 2 , Jong-Hyeob Baek 4 , Junggeun Jhin 4 , Jonghan Song 3
1 Materials Science and Engineering, korea univ., seoul Korea (the Republic of), 3 Advanced Analysis Center, Korea Institute of Science and Technology, Seoul Korea (the Republic of), 2 Institute of Physics and Applied Physics, Yonsei University, Seoul Korea (the Republic of), 4 LED Device Team, Korea Photonic Technology Institute, Gwangju Korea (the Republic of)
Show Abstract9:00 PM - K5.3
Transition Metal-doped GaN Nanostructures grown by Metalorganic Chemical Vapor Deposition
Shalini Gupta 1 , Yong Huang 1 , Hun Kang 1 , Matthew Kane 2 1 , Ian Ferguson 1 2
1 Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 2 Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Show Abstract III-V diluted magnetic semiconductors (DMS) have attracted attention in recent years since they offer the potential to fabricate room temperature spintronic devices such as integrated chip-based magnetic memories, reconfigurable logic elements, and polarized light emitters. Several studies have been performed on thin films and bulk crystals GaN doped with transition metals such as manganese. However, the potential of transition metal alloyed GaN nanostructures has yet to be explored. Ferromagnetic nanostructures offer the possibility of fabricating efficient multifunctional devices, which would have enhanced optical, electrical, and magnetic properties. This work presents the MOCVD growth and characterization of optically active GaN nanostructures that have been doped with Mn and Fe for potential spintronic applications. The diluted magnetic semiconductor nanostructures were grown on smooth AlN (6 Å) buffer layers deposited on (0001) sapphire substrate. A novel growth method has been developed to produce optically active GaN-based nanostructures using a two-step process. First, GaN is deposited at low growth temperatures (< 850oC) and low V-III ratios (< 30). This is followed by an in-situ activation step in which the temperature is ramped up to 970°C in a nitrogen atmosphere. Stranski-Krastanow – like growth is demonstrated for these nanostructures. The presence of GaN A1(LO) mode via Raman spectroscopy confirms the high crystalline quality of these layers. A red shift in observed in the GaN PL peak for most of the as-grown nanostructures due to an internal piezoelectric effects. GaN:Mn and GaN:Fe nanostructures were grown by introducing Cp2Mn or Cp2Fe to the growth chamber under optimal conditions for the formation of nanostructures. Atomic force microscopy (AFM) images revealed that increasing the percentage of Mn enhances nucleation as the nanostructures density increases and the lateral size decreases. Unlike the GaN nanostructures, an annealing step was not necessary to provide small, high density nanostructures. Similar results were observed when Fe was incorporated into GaN nanostructures. AFM measurements revealed that Fe, like Mn, affected the surface morphology of the nanostructures. The presence of Fe leads to suppression of adatom migrations due to altering of the surface free energy, thereby enhancing island formation and 3-dimensional growth. Magnetization measurements revealed a room temperature ferromagnetic component in the GaN:Fe nanostructures. The magnetization and coercivity increased as the amount of Fe incorporated increased. The origin of this ferromagnetic component may be related to either a ferromagnetic DMS component, or self-assembled Fe-Fe type clusters embedded within the nanostructures.
9:00 PM - K5.4
Spin Polarization of Diluted Magnetic Semiconductors under the Impurity Photoexcitation.
Manuela Vieira 1 , Peter Gorley 2 , Vitalii Dugaev 3 4 5 , Jozef Barnas 6 7 , Paul Horley 2 , Oksana Mysliuk 2
1 DEETC, Instituto Superior de Engenharia de Lisboa, Lisbon Portugal, 2 Dept. of Electronics and Energy Engineering, Chernivtsi National University, Chernivtsi Ukraine, 3 Dept. of Mathematics and Applied Physics, University of Technology, Rzeszów Poland, 4 Dept. of Physics and CFIF, Instituto Superior Técnico, Lisbon Portugal, 5 , Institute for Problems of Material Science, Chernivtsi Ukraine, 6 Dept. of Physics, AM University, Poznan Poland, 7 , Institute of Molecular Physics PAS, Poznan Poland
Show AbstractOne of the most efficient methods to control and manipulate spin polarization in diluted magnetic semiconductors (DMS) is controllable illumination with polarized light. There is currently a need to develop a theory to explain existing experimental data, taking into the account the long-time relaxation (LTR) mechanisms. In this paper we propose a system of kinetic equations which describe dynamics of the nonequilibrium spin systems of band electrons and electrons occupying the impurity levels. It is assumed that the semiconductor is illuminated with the polarized light of frequency corresponding to the impurity absorption. The presence of LTR processes is taken into account for band electrons and magnetic ions, together with the processes of thermal impurity ionization and spin-spin interaction of the band and impurity electrons. We present analytical expressions to determine the spin polarization degrees of band electrons he through the spin polarization hs of magnetic ions. The stationary space-inhomogeneous distributions of spin-polarized electron concentrations and polarization degrees he and hs are studied numerically as a function of the polarization type (clockwise, counter-clockwise, linear) and intensity of light, magnitude of the LTR times, etc. We calculated the dynamics of the spin subsystem using parameters typical of InP:Fe. It is shown that the distribution of electron concentration in thick films shows damped oscillations, the amplitude of which coincides with the stationary space-homogeneous distribution on the back side of the sample (opposite to the illuminated side). The concentration of spin-polarized band electrons is by more than four orders of magnitude larger than the intrinsic carrier concentration. The linear-polarized light enhances the concentration of the band electrons three times due to the transitions between the impurity level and conduction band; counter-clockwise polarized light allows to obtain two-times higher concentrations, while the clockwise polarized light enhances the concentration only by 150%. The results are in good agreement with existing experiments. This work was partially supported by the STCU grant #3098.
9:00 PM - K5.5
Evidence of Hole-mediated Double Exchange Ferromagnetism in GaN:Mn Nanowires.
Han-Kyu Seong 1 , Tae-Hyun Lee 1 , Tae-Eon Park 1 , Ryong Ha 1 , Han-Nah Jeong 1 , Heon-Jin Choi 1
1 School of Advanced Materials Science and Engineering, Yonsei University , Seoul Korea (the Republic of)
Show Abstract9:00 PM - K5.6
Search for Room Temperature Diluted Magnetic Semiconductor in Transition Metal Doped ZnS.
Yousong Gu 1 , Xueqiang Wang 1 , Jianming Li 1 , Yue Zhang 1
1 Department of Material Physics and Chemistry, University of Science and Technology Beijing, Beijing, Beijing, China
Show Abstract9:00 PM - K5.7
Effects of Annealing on Structural and Magnetic Properties of Cobalt Implanted TiO2 Thin Films.
Sai Peng Wong (deceased January 2007) 1 3 , Wing Yan Luk 1 , Quan Li 2 3 , Ning Ke 1 , Joerg Lindner 4
1 Dept of Electronic Engineering, The Chinese University of Hong Kong, Shatin Hong Kong, 3 Materials Science & Technology Research Centre, The Chinese University of Hong Kong, Shatin Hong Kong, 2 Dept of Physics, The Chinese University of Hong Kong, Shatin Hong Kong, 4 Institut fur Physik, University of Augsburg, Augsburg Germany
Show Abstract9:00 PM - K5.8
Effect of Al Doping in Room Temperature Ferromagnetic Zn(0.95-x)Co(0.05)Al(x) Diluted Magnetic Smiconductors.
Sanjukta Ghosh 1 , Sayak Ghoshal 2 , P. Anilkumar 2
1 Experimental Condensed Matter Physics, Institute of Physics, Bhubaneswar, Orissa, India, 2 Physics, Indian Institute of Science, Bangalore, Karnataka, India
Show Abstract
Symposium Organizers
Cammy R. Abernathy University of Florida
Salah Bedair North Carolina State University
Pierre Ruterana SIFCOM-ENSICAEN
Rachel Frazier Naval Research Laboratory
K6: Transition Metal Doped DMS
Session Chairs
Thursday AM, April 12, 2007
Room 3009 (Moscone West)
9:30 AM - K6.1
Behavior of Excitonic Luminescence in P:ZnMnO Treated by RTA.
A Ryoung Lee 1 , Uiseok Jung 1 , Jihoon Kim 1 , Junje Seong 1 , Hajong Bong 1 , Young Min Lee 1 , Hoon Young Cho 1 , Deuk Young Kim 1 , Sejoon Lee 2 , Youn Hwan Lee 3
1 Quantum-functional Semiconductor Research Center, Dongguk University, Seoul Korea (the Republic of), 2 Institute of Industrial Science, University of Tokyo, Tokyo Japan, 3 Information Communication Engineering, Dongguk University, Gyeongju Korea (the Republic of)
Show Abstract9:45 AM - K6.2
P+-ion Impantation into ZnMnO Thin Film and its Ferromagnetic Properties.
Hajong Bong 1 , Uiseok Jung 1 , A Ryoung Lee 1 , Jihoon Kim 1 , Junje Seong 1 , Young Min Lee 1 , Hoon Young Cho 1 , Deuk Young Kim 1 , Sejoon Lee 2 , Youn Hwan Lee 3
1 Quantum-functional Semiconductor Research Center, Dongguk University, Seoul Korea (the Republic of), 2 Institute of Industrial Science, University of Tokyo, Tokyo Japan, 3 Information Communication Engineering, Dongguk University, Gyeongju Korea (the Republic of)
Show Abstract10:00 AM - K6.3
The Fine Structure of the Mn Distribution in ZnO Layers Deposited by Magnetron Sputtering for Spintronic Application.
Pierre Ruterana 1 , Chunli Liu 2 , Hadis Morkoç 3
1 SIFCOM, ENSICAEN, Caen France, 2 School of Physics and Astronomy, Seoul National University, Seoul Korea (the Republic of), 3 Electrical Engineering, Virginia Commonwealth University, Richmond, Virginia, United States
Show Abstract10:15 AM - K6.4
Chemical Control of Lattice Defect Formation and High-TC Ferromagnetism in Oxide Diluted Magnetic Semiconductors.
Daniel Gamelin 1
1 Chemistry, University of Washington, Seattle, Washington, United States
Show AbstractDiluted magnetic semiconductors (DMSs) are pivotal architectural elements in many proposed spintronics devices. In particular, wide band gap DMSs are being intensely investigated for their potential use in high-temperature spintronics technologies, but such applications have been hindered by their inconsistent magnetic properties. This talk will summarize our group's recent findings related to: (a) Direct chemical synthesis and magneto-optical spectroscopy of DMS nanostructures(b) Chemical manipulation of room-temperature spin ordering in oxide DMSs(c) Charge transfer electronic structures of oxide DMSsApart from the technological advantages of reliable, controllable, and even switchable high-TC ferromagnetic semiconductors, this research is motivated by the new fundamental insights it provides into the microscopic origins of ferromagnetism in this class of materials.Related references:(1) Kittilstved, K. R.; Schwartz, D. A.; Tuan, A. C.; Heald, S. M.; Chambers, S. A.; Gamelin, D. R. "Direct Kinetic Correlation of Carriers and Ferromagnetism in Co2+:ZnO." Phys. Rev. Lett., 2006, 97, 037203.(2) Kittilstved, K. R.; Liu, W. K.; Gamelin, D. R. "Electronic Structure Origins of Polarity Dependent High-TC Ferromagnetism in Oxide Diluted Magnetic Semiconductors." Nature Materials, 2006, 5, 291-297.(3) Archer, P. I.; Radovanovic, P. V.; Heald, S. M.; Gamelin, D. R. "Low-Temperature Activation and Deactivation of High-TC Ferromagnetism in a New Diluted Magnetic Semiconductor: Ni2+-Doped SnO2." J. Am. Chem. Soc., 2005, 127, 14479-14487.(4) Kittilstved, K. R.; Norberg, N. S.; Gamelin, D. R. "Chemical Manipulation of 300K Ferromagnetism in ZnO Diluted Magnetic Semiconductors." Phys. Rev. Lett., 2005, 94, 149049.
10:30 AM - K6.5
Mn2+ in n-type ZnO Thin Films by MOCVD: a Classical II-VI DMS.
Ekaterine Chikoidze 1 2 , Yves Dumont 1 , Jurgen Von Bardeleben 3 , Jerome Glieze 4 , Ouri Gorochov 1 , Edouard Rzepka 1
1 GEMAC, CNRS, MEUDON France, 2 material Science Department, Tbilisi Stet university, Tbilisi Georgia, 3 CNRS, Institut des Nanosciences de Paris (INSP, Paris France, 4 Laboratoire de Physique des Milieux Denses, Université de Metz, Metz France
Show Abstract10:45 AM - K6.6
Correlations Between Optical Transmission and Magnetic Properties of Doped and Undoped GaMnN.
Salah Bedair 1 , Erdem Arkun 2 , Mason Reed 1 , John Muth 1 , X. Zhang 1 , Nadia El-Masry 2
1 Dept of Electrical and Computer Engineering, North Carolina State University, Raleigh, North Carolina, United States, 2 Materials Science and Engineering Department, NC State University, Raleigh, North Carolina, United States
Show Abstract GaMnN films undoped, silicon and Mg doped were grown by MOCVD on (0001) sapphire substrates. The magnetic properties were measured at room temperature by SQUID. Optical transmission measurement was carried out and two Mn related absorption bands were observed. The first (band I) was centered on 1.5 eV above the valence band. The second band (band II) is fairly broad and started at about 2 eV above the valence band and extended close to the conduction band. The absorption at these bands was found to scale with the thickness of the GaMnN film and the Mn concentrations. We have also observed that transmission through these bands depend on the nature of the Si or Mg and the doping levels. A fairly weak correlation was observed between the band located at 1.5 above EV and the magnetic properties of these GaMnN films.These optical transmission data will be explained based on the location of the Fermi level in the GaMnN band gap. For example heavy silicon doping will move the Fermi level closer to the conduction band resulting in a decrease in the magnetic properties and the optical absorption band I . Similar correlations were also observed for Mg doping. These optical measurements will be useful in developing better understanding of the role of the mediated carriers on the ferromagnetic properties of GaMnN.
11:30 AM - K6.7
Optimal Doping Control of High-Tc Magnetic Semiconductors via Subsurfactant Epitaxy.
Zhenyu Zhang 1 2 , Changgan Zeng 2 , Klaus van Benthem 1 , Matthew Chisholm 1 , Wenguang Zhu 2 , Hanno Weitering 2 1
1 Materials Science & Technology Division, ORNL, Oak Ridge, Tennessee, United States, 2 Department of Physics and Astronomy, The University of Tennessee, Knoxville, Tennessee, United States
Show Abstract11:45 AM - K6.8
Investigating the Origin of Room-temperature Ferromagnetism in 1D GeMn.
Olga Kazakova 1 , Jaideep Kulkarni 2 , Donna Arnold 2 , Justin Holmes 2
1 , NPL, Teddington United Kingdom, 2 , UCC, Cork Ireland
Show Abstract12:00 PM - K6.9
Magneto-photoluminescence in Mn-ion Implanted Silicon Nanocrystals.
Wei Pan 1 , M. Carroll 1 , Y. Wang 2
1 , Sandia National Labs, Albuquerque, New Mexico, United States, 2 Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show Abstract12:15 PM - K6.10
Enhanced Room Temperature Ferromagnetism in Co- and Mn-Ion Implanted Silicon
Joonsung Lee 1 , Jeongwon Park 1 , Sungho Jin 1 , Se Ahn Song 2 , Prabhakar Bandaru 1
1 Materials Science program, UC, San Diego, La Jolla, California, United States, 2 Analytical Engineering Center, Samsung Advanced Instite of Technology, Suwon Korea (the Republic of)
Show AbstractFurther progress in the rapidly advancing field of spintronics is critically dependent on the availability of room temperature magnetic semiconductors. We report here, for the first time, on the occurrence of ferromagnetism at room temperature, in cluster–free cobalt and manganese ion implanted crystalline silicon. Room temperature magnetism has been measured by Alternating Gradient Magnetometry (AGM) and confirmed through SQUID magnetometry. Structural analysis, with high-resolution Transmission Electron Microscopy (HRTEM) and Rutherford Backscattering spectroscopy (RBS), has been used to rule out cluster and extraneous phase formation.Through magnetic and structural analysis it has been shown that the ion implanted Si consists of two layers of Co- and Mn-containing silicon: (1) an amorphous Si layer on the surface, and (2) single crystalline Si beneath. The amorphous layer shows very little magnetism by itself, but seems to be responsible for partially canceling out or masking the ferromagnetism in the crystalline Si. We also observe that etching of the amorphous Si layer dramatically enhances the measured magnetism, by as much as 400%. The temperature variation of the magnetic properties and possible origins of the observed magnetism in terms of currently accepted models will be presented.
12:30 PM - K6.11
Correlation Between Ferromagnetism and Cluster Formation in (Zn,Cr)Te co-doped with Charge Impurities.
Shinji Kuroda 1 , Nozomi Nishizawa 1 , Koki Takita 1 , Masanori Mitome 2 , Yoshio Bando 2
1 Institute of Materials Science, University of Tsukuba, Tsukuba, Ibaraki, Japan, 2 Advanced Materials and Nanomaterials Laboratories, National Institute for Materials Science, Tsukuba, Ibaraki, Japan
Show Abstract