4:30 PM - **WW10.5
Strained EuTiO3 Confirmed to be a Strong Ferroelectric Ferromagnet.
June Hyuk Lee 1 2 , Lei Fang 3 , Xianglin Ke 4 , Eftihia Vlahos 2 , Young Woo Jung 3 , Lena Fitting Kourkoutis 5 , Philip Ryan 6 , John Freeland 6 , Tassilo Heeg 1 , Martin Roeckerath 7 , Veronica Goian 8 , Margitta Bernhagen 9 , Reinhard Uecker 9 , P. Chris Hammel 3 , Karin Rabe 10 , Stanislav Kamba 8 , Jürgen Schubert 7 , David Muller 5 , Craig Fennie 5 , Venkat Gopalan 2 , Peter Schiffer 4 , Ezekiel Johnston-Halperin 3 , Darrell Schlom 1
1 Department of Materials Science and Engineering, Cornell University, Ithaca, New York, United States, 2 Department of Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania, United States, 3 Department of Physics, Ohio State University, Columbus, Ohio, United States, 4 Department of Physics, Pennsylvania State University, University Park, Pennsylvania, United States, 5 Department of Applied and Engineering Physics, Cornell University, Ithaca, New York, United States, 6 Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois, United States, 7 Institute of Bio and Nanosystems, Research Centre Jülich, Jülich Germany, 8 , Institute of Physics ASCR, Prague Czech Republic, 9 , Leibniz Institute for Crystal Growth, Berlin Germany, 10 Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey, United States
Show AbstractWe report the emergence of a multiferroic ground state in biaxially strained EuTiO3 thin films in agreement with theory. Biaxial strain was predicted to induce a strong simultaneously ferromagnetic (spontaneous magnetization ~7 µB/Eu) and ferroelectric (spontaneous polarization ~10 µC/cm2) state in EuTiO3 due to spin-phonon coupling [1]. To confirm these predictions, we have grown epitaxial EuTiO3 films on (001) LSAT, (001) SrTiO3, and (110) DyScO3 substrates by reactive molecular-beam epitaxy (MBE) [2]. These substrates impart biaxial strains of −0.9%, 0.0% and about +1.1%, respectively. EuTiO3 on SrTiO3 is unstrained and EuTiO3 on DyScO3 is sufficiently strained in biaxial tension that it should be in the desired multiferroic state according to prediction. MBE growth of EuTiO3 was achieved by the codeposition of europium and titanium onto the substrates under an oxygen background partial pressure of 3×10-8 Torr at a substrate temperature of 650 °C. X-ray diffraction revealed phase-pure, epitaxial (001)-oriented EuTiO3 thin films commensurately strained to the substrates they were grown on. The rocking curve full width at half maximum values were as narrow as 8 arc sec (0.0022°). Scanning transmission electron microscopy revealed epitaxial films with abrupt interfaces between film and substrate. Electron energy loss spectroscopy and x-ray absorption spectroscopy confirmed the desired Eu2+ and Ti4+ oxidation state of the EuTiO3 films. Optical second harmonic generation revealed that the unstrained EuTiO3 on SrTiO3 was not polar, as expected, but the strained EuTiO3 on DyScO3 exhibited a paraelectric-to-ferroelectric phase transition at 250 K to a polar point group where domain switching by electric fields was observed. Far-infrared reflectance measurements revealed a soft mode anomaly and therefore dielectric constant exhibited maximum around 250 K. Magneto-optic Kerr effect and SQUID measurements showed that the unstrained EuTiO3 was antiferromagnetic with TN=5.5 K in agreement with bulk unstrained EuTiO3, whereas the strained EuTiO3 on DyScO3 was ferromagnetic with TC=4.2 K. Our results thus demonstrate a strong ferromagnetic ferroelectric state in strained EuTiO3 that is fully consistent with the predicted spin-lattice coupling mechanism [1].[1] C.J. Fennie and K.M. Rabe, Phys. Rev. Lett. 97, 267602 (2006).[2] J.H. Lee et al., Nature 466, 954 (2010).
9:00 PM - WW11.17
Raman Scattering and Magnetic Resonance Studies of Nanocrystalline KTaO3.
Iryna Golovina 1 , Ilia Geifman 2 , Vadim Bryksa 1 , Victor Strelchuk 1 , Alexandr Andriiko 3
1 , Institute of Semiconductor Physics of NASU, Kiev Ukraine, 2 , Quality Engineering Education, Inc. , Buffalo Grove, Illinois, United States, 3 , National Technical University of Ukraine “KPI”, Kiev Ukraine
Show AbstractNew multiferroics, i.e. materials, where such types of ordering as ferroelectricity and ferromagnetism can coexist, are presently the subject of growing interest. From potential application’s point of view, especially attractive are the materials, in which room temperature ferromagnetism is observed. Single-crystal potassium tantalate is an incipient ferroelectric, which does not undergo a ferroelectric phase transition down to 0 K. However, in nanosized crystals, which most recently have been synthesized by Dr. Andriiko’s group, some interesting effects were observed. Firstly, a wide maximum, within 20-30 K, was observed in the temperature dependence of dielectric constant. Since the dielectric peak did not shift to higher temperature as the measuring frequency was increased from 25 Hz to 1 MHz, it was suggested that an ordering transition takes place. Secondly, a ferromagnetic resonance (FMR) spectrum was registered at room temperature on the same sample. Last result indicates occurrence of a coupling between individual spins, which leads to a long-range magnetic order [1]. In the present work we report on two spectroscopic studies of undoped nanocrystalline potassium tantalate, micro-Raman spectra obtained in the temperature interval 4.2
9:00 PM - WW11.18
Self-assembled Oxide Nano-scaffolds for Enhanced Ferroelectricity in Thick Barium Titanate Films.
Sophie Harrington 1 , Zhenxing Bi 2 , Haiyan Wang 2 , SeungHyub Baek 4 , Chang-Beom Eom 4 , Sava Denev 5 , Venkatraman Gopalan 5 , Junyi Zhai 3 , Quanxi Jia 3 , Judith Macmanus-Driscoll 1
1 Department of Materials Science and Metallurgy, University of Cambridge, Cambridge United Kingdom, 2 Department of Electrical and Computer Engineering, Texas A and M University, Houston, Texas, United States, 4 Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States, 5 Department of Materials Science and Engineering, Pennsylvania State University, State College, Pennsylvania, United States, 3 Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractThe tetragonal to cubic phrase transition in barium titanate that naturally occurs around 120oC has been suppressed up to 800oC in thick, > 1μm, films. A self-assembled oxide nanoscaffold has been used to clamp the barium titanate unit cell with >1% out of plane strain, resulting in enhanced ferroelectric properties and reduced leakage. Films were deposited by pulsed laser deposition on SrTiO3 and characterised via TEM, high temperature XRD, SHG and direct electrical measurement.
9:00 PM - WW11.19
Phase-field Simulation of Strain-induced Magnetic Domain Switching in Epitaxial Cobalt Rerrite Thin Films.
Jiamian Hu 1 2 , Guang Sheng 2 , Jingxian Zhang 2 , Cewen Nan 1 , Longqing Chen 2
1 Materials Science and Engineering, State Key Lab of New Ceramics and Fine Processing, Tsinghua University, Beijing China, 2 Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania, United States
Show AbstractThe effect of biaxial in-plane strains on the magnetic domain structures of the epitaxial CoFe2O4 (CFO) thin films is studied using phase-field simulations. The results show that the magnetic domains of the CFO thin films can be switched from an initial in-plane to an out-of-plane direction under the action of in-plane elastic strains. An abrupt or gradual domain switching feature is exhibited for the single-domain and multi-domain CFO thin films, respectively. Typical magnetic domain structures as a result of the isotropic in-plane strains are presented. Such strain-induced magnetic domain switching in magnetic thin films provides routes for an electric-field tuning of magnetic domain structures in artificial magnetic/ferroelectric multiferroic heterostructures through piezoelectrically controlled strains.
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Comparisons and Analyses on Heterostructures Consisting of ZnO and Different Ferroelectric Films.
Nai-wen Zhang 1 , Ze Jia 1 , Ming-ming Zhang 1 , Tian-ling Ren 1
1 , Institute of Microelectronics, Tsinghua National Laboratory for Information Science and Technology, Beijing China
Show AbstractHeterostructures consisting of ferroelectric and semiconductor have been widely studied for its application in the ferroelectric field effect transistor. A charge carriers accumulation layer or depletion layer is formed in the semiconductor, depending on the orientation of ferroelectric polarization in the gate. In this work, two different types of ferroelectric/semiconductor heterostructures, made up of Pb(Zr,Ti)O3/ZnO (Zinc Oxide) and BiFeO3/ZnO respectively, were fabricated by sol-gel process. Their electrical properties were tested and showed a great difference. The mechanisms of different behaviors were proposed and the influencing factors were investigated.The ferroelectric/semiconductor structures were prepared by means of multilayer spin-coating. First, BiFeO3 and Pb(Zr,Ti)O3 ferroelectric thin films were deposited and crystallized on the Pt/Ti/SiO2/Si respectively. Then, ZnO film was prepared and annealed on the top of ferroelectric layer. After that, Pt top electrodes were fabricated on ZnO for the electrical property measurement. The current-voltage characteristics and capacitor-voltage relations of the two different heterostructures were measured. The crystallization conditions of the materials were examined by XRD (X-ray diffraction). Interface and surface topologies were tested by SEM (scanning electron microscope).Obvious diodelike behavior were observed in the BiFeO3/ZnO heterostructures when current-voltage characteristics were measured, while Pb(Zr,Ti)O3/ZnO heterostructures exhibited a symmetrical behavior. The hysteresis loops and capacitor-voltage relations of the two kinds of heterostructures were compared. Different electrical properties reveal that coupling mechanism between two ferroelectric materials and ZnO were different. Based on this, the mechanisms of different behaviors in ferroelectric/semiconductor heterostructures were proposed. Besides, different interfacial conditions were observed, which are also believed to be factors influencing electrical properties of the structures.
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Influence of Strain and Doping on the Structural and Ferroelectric Properties of Bismuth Ferrite Thin Films.
Florian Johann 1 , Alessio Morelli 1 , Miryam Arredondo 1 , Ionela Vrejoiu 1
1 , MPI of Microstructure Physics, Halle Germany
Show AbstractBiFeO3 (BFO) is at present the only known multiferroic perovskite at room temperature and therefore interesting for both fundamental research and applications. Large single crystals of BFO are difficult to grow and suffer from high leakage currents. It has been reported that many properties along with control of the ferroelectric/ferroelastic domain patterns can be improved by substituting Bi or Fe with other elements and growing BFO as heteroepitaxial films on suitably chosen substrates.We studied the influence of different strain states and dopants for various properties such as the ferroelectric domains and the spontaneous polarization. Pulsed laser deposition was used to grow epitaxial thin BFO films on different single crystals substrates such as SrTiO3 (100), DyScO3 (110), GdScO3 (110) or SmScO3 (110). Hence, we obtained a variety of strained films with an in-plane strain ranging from -1.4% to +0.75%. For electrical measurements a SrRuO3 bottom electrode layer was grown in-between. In order to study the doping effect, lanthanum and manganese doped BFO targets were used to produce films with doping on the A-site and B-site, respectively.X-ray diffraction and high resolution transmission electron microscopy measurements were performed to investigate the structure and quality of the films. The spontaneous polarization was measured macroscopically and piezoresponse force microscopy measurements were carried out to study the ferroelectric domain patterns and piezoelectric properties microscopically. This set of studies aims to yield an overview about the influence of different strain states and dopants on epitaxial bismuth ferrite thin films.
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Bias-induced Hysteresis and Nanoscale Multiferroic Properties in [Pr(La)]1-xCaxMnO3 Studied by Scanning Force Microscopy.
F. Figueiras 1 , V. Amaral 1 , D. Karpinsky 2 , N. Panwar 2 , P. Maksymovych 3 , S. Kalinin 3 , A. Kholkin 2
1 Dept. of Physics & CICECO, University of Aveiro, Aveiro Portugal, 2 DECV & CICECO, University of Aveiro, Aveiro Portugal, 3 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractOne of the proposed driving mechanisms for ferroelectricity in multiferroics is the occurrence of charge and orbital ordering that break inversion symmetry. Half-doped charge ordering manganite systems, like (Pr1-xCax)MnO3 or La1-xCaxMnO3 near x≈0.5 Ca content, were set forth as prototype systems for induced electronic ferroelectricity mechanism, associated with the appearance of site- and bond-centered orbital ordering (bond dimerization) or spin dimerization, respectively. However, the finite conductivity of these systems hinders an observation of possible macroscopic polarization study as direct proof of ferroelectricity. Considering that the polarization can exist in nanoscale volumes, we used the Piezoresponse Force Microscopy (PFM) [1] for studying local electrical and electromechanical properties of manganites. This (lock-in based) technique allows measurements of local hysteresis loops at the resolution of 10 nm level by detection of local piezoelectric deformation induced by an external electric field. Our previous results in La0.89Sr0.11MnO3 [2] are extended to (Pr1-xCax)MnO3 and La0.5Ca0.5MnO3 systems where a clear bias-induced piezocontrast and local hysteresis loops could be investigated provided evidence of the existence of a locally induced polar state with ferroelectric response even above the charge order transition. The microscopic mechanisms associated with these bias-induced modifications, which may be associated to the presence of nanoscopic CO regions, are discussed in terms of a charge doping process, according to the bias polarity dependence, and of the role of charge/ionic or oxygen vacancies motion mechanisms. The different time-scales associated with piezoelectric (electronic) deformations and with ionic electrodiffusion in the materials is discussed to elucidate the possible electrochemical strain effects. The possibility of producing single domain electronic phase transitions opens a new pathway to achieve spatially localized multiferroic studies (electronic reconstruction and phase control at interfaces) and widens the possibilities of high density memory applications, by the ability to create artificial multiferroic materials for memory cells. The authors from Portugal are thankful to Fundação para a Ciência e a Tecnologia (project PTDC/ FIS/105416/2008) for the financial support. This research is supported by the Center for Nanoscale Materials Sciences (CNMS) at the Oak Ridge National Laboratory and was part of a CNMS User Program.[1] S. V. Kalinin, N. Setter, A. L. Kholkin, MRS Bulletin 34, 634 (2009). [2] R. Mamin, I. K. Bdikin, A. L. Kholkin, Appl. Phys. Lett. 94, 222901 (2009).
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Fabrication and Characterization of Novel Room Temperature Relaxor Magneto-electric Multiferroics.
Ashok Kumar 1 , Ram Katiyar 1 , Jim Scott 1 2
1 PHYSICS, University of Puerto rico, San Jaun, Puerto Rico, United States, 2 , University of Cambridge, Cambridge United Kingdom
Show AbstractDesign of novel single phase materials and their development of practical magnetoelectric multiferroic devices for industry have stand on two pillars: The first is for weak-field sensors and second is for random access memory (RAM) elements. We have fabricated a variety of “PZT-PFW” (PbZr0.52Ti0.48O3)1-x(PbFe2/3W1/3O3)x [PZTFWx; 0.2 < x < 0.4] single-phase tetragonal ferroelectrics via chemical solution deposition (CSD) [polycrystalline] and pulsed laser deposition (PLD) [epitaxial] onto Pt/Ti/SiO2/Si(100) and SrTiO3/Si substrates. These exhibit ferroelectricity and (weak) ferromagnetism above room temperature with strain coupling via electrostriction and magnetostriction. Application of modest magnetic field strength (µ0H < 1.0 Tesla) destabilizes the long-range ferroelectric ordering and switches the polarization from ca. 35 µC/cm2 (0.35 C/m2) to zero (relaxor state). This offers the possibility of three-state logic (+P, 0, -P). MMIS device structures of Pt/PZTFWx/SrTiO3/Si (111) showed good memory windows(3-4V), suggesting good candidates for multiferroic RAMs.
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Room-temperature Multiferroic Properties of Bismuth Manganite Thin Film.
Wei-Cheng Kuo 1 , Chang-Yang Kuo 3 , Heng-Jui Liu 3 , Hong-Ji Lin 3 , Ying-Hao Chu 2 , Yi-Chun Chen 4 , Tzeng-Ming Uen 1 , Jenh-Yih Juang 1
1 Electrophysics, National Chiao Tung University, Hsinchu Taiwan, 3 , National Synchrotron Radiation Research Center, Hsinchu Taiwan, 2 Materials Science and Engineering, National Chiao Tung University, Hsinchu Taiwan, 4 Physics, National Cheng Kung University , Tainan Taiwan
Show AbstractMultiferroic materials, which possess coupled electric, magnetic and structural order parameters in the same phase, have attracted considerable attention among strong-correlated complex oxide systems. These materials are not only interesting from a scientific point of view but promising in novel application possibilities. In previous study, low temperature multiferroic properties in perovskite type BiMnO3(BMO) has been demonstrated. In this work, through epitaxial strains exerted by LaAlO3 single crystal substrate, we successfully demonstrate the growth the c-axis oriented new phase in BMO thin film. After the deposition, HRXRD has been used to characterize the lattice structure, which show new fascinating phase that are different from the papers early reported. We further revealed manganese valence through the X-ray Magnetic Linear Dichroism (XMLD) measurement and exhibit the mixed +3 and +4 valence of manganese. High quality expitaxy and sharp interface could be observed by Transmission electron microscopy. With LaNiO3 bottom electrode, room-temperature ferroelectricity is demonstrated by Piezoelectric Force Microscopy (PFM), which revealed the reversible ferroelastic switching through the external electrical bias. M-H curves are measured by SQUID magnetometer (Quantum Design, MPMS) as a function of temperatures. Ferromagnetic behaviors have been probed from room temperature (300K) to low temperature (10K), furthermore, 5 emu/cc of saturation magnetization at 300K has been observed. In our preliminary results, room temperature ferroelectric and ferromagnetic properties could be coexistent in single phase material through epitaxial strain, thus provide a modeling system to study the multiferroic material and a powerful candidate for the next-generation electronic devices.
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Characteristics of BiFeO3/LaNiO3 Multiferroic Superlattices Structure Prepared by RF Sputtering.
Yen-Ting Liu 1 , Hsin-Yi Lee 2 3 , San-Yuan Chen 2
1 , Program for Science and Technology of Accelerator Light Source, National Chiao Tung University, Hsinchu Taiwan, 2 , National Synchrotron Radiation Research Center, Hsinchu Taiwan, 3 , Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu Taiwan
Show AbstractArtificial superlattices structure consisting of multiferroic BiFeO3 (BFO) and conductive LaNiO3 (LNO) were epitaxial grown on SrTiO3 (001) single crystal substrates at temperatures in the range of 560–810°C by a RF magnetron sputtering system. X-ray reflectivity and high-resolution diffraction measurements were employed to characterize the microstructure of these films. The 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 BFO/LNO artificial superlattice structure formed on a SrTiO3 substrate at all temperature of deposition. The higher is the temperature of deposition, the smaller are the full width at half-maximum of the in-plane rocking curve and the better the crystalline quality. 710°C was the best temperature of the growth condition. The fitted result from x-ray reflectivity curves shows that the densities of the BFO and LNO sublayers are slightly less than their bulk values. X-ray measurements show that these superlattice films become subject to greater tensile stress along the c-axis, increased compressive stress parallel to the surface plane and increased crystalline quality with increasing the temperature.
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Electric Field-mediated Magnetic Coercivity in Magnetoelectric Bilayer: A Novel Memory Cell.
Zheng Li 1 , Jing Wang 1 , Yuanhua Lin 1 , Ce-wen Nan 1
1 Dept. Materials Science &Engineering, Tsinghua University, Beijing, Beijing, China
Show AbstractA multiferroic magnetoelectric bilayer with Fe0.93Ge0.07 film grown on fully-poled ferroelectric BiScO3-PbTiO3 (BSPT) substrate was fabricated. The magneto-optical Kerr effect measurement on the heterostructures demonstrated that the magnetism of the FeGe thin film can be manipulated by switching the electric voltage applied on the ferroelectric substrate, with a large change in the magnetic coercive field of the FeGe thin film. We present a novel magnetic memory cell in which electric-field-induced two different coercive-field Hc states (i.e., low-Hc and high-Hc) rather than magnetization states are used to write data bits. The FeGe/BSPT bilayer is used for illustration of such a prototype electric-write/magnetic-read memory cell which is nonvolatile. The reading process of the two different coercive-field Hc states information written by electric field is also presented by using magnetoresistance read head.
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Magnetic Properties of Self-assembled Epitaxial Nanocomposite Thin Films via a Chemical Solution Approach.
Hongmei Luo 1 , Stacy Baber 1 , Qianglu Lin 1
1 Chemical Engineering, New Mexico State University, Las Cruces, New Mexico, United States
Show AbstractAmong the family of spinel ferrite materials, cobalt ferrite (CoFe2O4) has received much attention due to its unique magnetic properties and its potential technological applications. The large magnetostriction coefficient makes CoFe2O4 an excellent candidate in composite materials. Self-assembled oxide nanocomposites CoFe2O4-SrTiO3, CoFe2O4-MgO, CoFe2O4-NiO, and CoFe2O4-Co3O4 thin films were grown on single crystal LaAlO3 substrates by a novel chemical solution approach of polymer-assisted deposition. The phase, epitaxy, strain and microstructure were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), and high resolution transmission electron microscopy (HRTEM). The magnetic properties were studied and compared with the single-phase CoFe2O4 films and those bi-layer thin films. The strain effects on the magnetic properties will be discussed.
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Tunable Low Field Magnetoresistance in (La0.7Sr0.3MnO3)0.5:(ZnO)0.5 Self-assembled Vertically Aligned Nanocomposite Thin Films.
Aiping Chen 1 , Zhenxing Bi 1 , Chen-Fong Tsai 1 , Xinghang Zhang 2 , Quanxi Jia 3 , Judith MacManus-Driscoll 4 , Haiyan Wang 1
1 Department of Electrical and Computer Engineering, Texas A&M University, College Station, Texas, United States, 2 Department of Mechanical Engineering, Texas A&M University, College Station, Texas, United States, 3 Center for Integrated Nanotechnologies (CINT), Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 4 Department of Materials Science and Metallurgy, University of Cambridge, Cambridge United Kingdom
Show AbstractTunable and enhanced low field magnetoresistance (LFMR) is observed in epitaxial (La0.7Sr0.3MnO3)0.5:(ZnO)0.5 (LSMO:ZnO) self-assembled vertically aligned nanocomposite (VAN) thin films, which grow on SrTiO3 (001) substrates by pulsed laser deposition (PLD). The enhanced LFMR properties of the VAN films reach as high as 30% at 1 T and 154 K. It is attributed to spin-polarized tunneling across the artificial vertical grain boundaries (GBs) introduced by the secondary ZnO nanocolumns. More interestingly, the vertical residue strain and the LFMR peak position of the VAN films can be systematically tuned by deposition frequency. The tunability of physical properties is associated with the vertical phase boundaries tuned as a function of the deposition frequency. The results suggest that the artificial vertical GB tuning in the unique VAN films with vertical ferromagnetic-insulating-ferromagnetic (FM-I-FM) tunneling structure provides a viable route to manipulate the magnetotransport properties in the VAN films with favorable epitaxial quality.
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Arrays of Oxide Nanostructures on Single Crystal Substrates Generated via Water Developable Electron Beam Lithography.
Josh Malowney 1 2 , Albert Calleja 1 , Jordi Arbiol 1 3 , Roger Guzman 1 , Francesc Belarre 1 , Jordi Llobert 2 , Narcis Mestres 1 , Teresa Puig 1 , Xavier Borrise 2 , Joan Bausells 2 , Xavier Obradors 1
1 Superconductors, Institute of Materials Science of Barcelona (ICMAB-CSIC), Barcelona Spain, 2 , National Center of Microelectronics (CNM-CSIC), Barcelona Spain, 3 , Catalan Institution for Research and Advanced Studies (ICREA), Barcelona Spain
Show AbstractControlled arrays of oxide nanostructures have been formed by spin coating a novel water developable precursor onto a single crystal substrate, then irradiating via an electron beam and followed finally by a high temperature pyrolysis step to form the nanocrystals. The precursor consists of a stoichiometric amount of La, Sr, and Mn in an aqueous nitrate solution, yielding La0.7Sr0.3MnO3 (LSMO), along with 5wt% polyvinyl alcohol. The reason for the PVOH is to form locally polymerized areas where the spun film is irradiated with doses greater than 0.5 mC/cm^2 [1]. The insulating single crystal substrates of SrTiO3, LaAlO3, and yttria stabilized ZrO2 (YSZ) were used to promote various amounts of localized strains on the grown nanoislands and nanowires. The precursor solution was confirmed to give epitaxial LSMO and yield a magnetic response in line with bulk values when spun and pyrolized on LaAlO3 as a thin film. The nanostructures which were written via electron beam range from nanoislands for radiation doses on the order of 1mC/cm^2 to nanowires at dosages larger than 220mC/cm^2. The nanoislands were investigated with AFM to show dimensions which are dosage dependent and on the order of 25 nm in height with a diameter of 150 nm and for the nanowires 30nm in height and 10 μm in length. The TEM analysis showed an epitaxial growth and the EELS analysis showed the nanostructures to be depleted of manganese which falls in line with previously reported results derived from other methods [2, 3]. By using SEM images at various stages of thermal treatment, the nanowires growth mechanism was studied and revealed to form at 800C and have a fast non-linear growth rate of 3 μm/hr for the first thirty minutes. This technique’s applicability was also confirmed by writing nanoislands and nanowires with a SrTiO3 precursor solution. AcknowledgementsThis work has been financed by the AGAUR grant resolution IUE/2681 and Consolider NANO-SELECT CSD 2007 00041References1.C. Chuang et al Nanotechnology 17 4399 (2006)2.A. Carretero et al Adv Func Mat 20 892 (2010)3.C. Moreno et al Adv Func Mat 19 2139 (2009)
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Relation between Electrical Properties and Structures of Ca2RuO4 and Sr2RuO4 Epitaxial Films on Various Perovskite Substrates.
Ludi Miao 1 , Wenyong Zhang 1 , Tijiang Liu 1 , Jin Peng 1 , Jin Hu 1 , Ilan Stern 1 , Xiaolan Zhou 1 , Punam Silwal 1 , Zhiqiang Mao 1 , Dae Ho Kim 1
1 Department of Physics and Engineering Physics, Tulane University, New Orleans, Louisiana, United States
Show AbstractLayered ruthenates, R2RuO4 (R=Ca, Sr) have attracted great attention for their richness in physical properties such as metal-insulator transition, magnetism, and superconductivity. Sr2RuO4 (SRO) shows tetragonal structure with orthogonal alignments of the RuO6 octahedrons leading to an unconventional spin-triplet-paired p-wave superconductor without doping. Several groups succeeded in growing high quality epitaxial films of SRO where the superconductivity was suppressed due to carrier trapping by disorders such as out-of-phase-boundaries. Only the films on lattice matching (LaAlO3)0.3(SrAl0.5Ta0.5O3)0.7 (LSAT) substrates with (001) orientation showed superconductivity. With smaller Ca cations replacing Sr, Ca2RuO4 (CRO) exhibits an orthorhombic structure with tilted octahedrons leading to insulating ground state. It is reported that epitaxial films of CRO on LaAlO3 (LAO) substrates with compressive strain showed metallic ground state. To investigate the effect of epitaxial strain on the structural and electrical transport properties, we have grown epitaxial c-oriented SRO and CRO films by pulsed laser deposition (PLD) on perovskite substrates with various lattice constants including SrTiO3, LSAT, NdGaO3, LaSrGaO4, and LAO all with (001) pseudo-cubic orientation. High resolution four circle X-ray diffraction (XRD) confirmed the structure and crystalline quality of the films. The resistivity was measured with varying temperature from 400K to 3K by 4-probe method. 20nm thick CRO film on a LAO substrate shows semiconducting transport behavior with metal to insulator transition around 200K. The transition temperature increases as increasing the thickness. On the other hand, SRO films on all substrates yield metallic behavior at the whole temperature range with occasional slight upturns at lower temperature in highly resistive samples. Residual resistivity at 3K of SRO films shows a sign of monotonic decrease with decreasing the full width at half maximum (FWHM) of the rocking curves. The FWHM strongly depends on the lattice mismatch between the films and the substrates. Our SRO film on LSAT with smallest lattice mismatch exhibits the narrowest rocking curve with FWHM of 0.02o and therefore the lowest residual resistivity of 6.6μΩcm. In-plane lattice constants of the films measured by reciprocal space maps of XRD show rapid relaxation of epitaxial strain in SRO grown on all substrates, in contrast to fully strained CRO films on both LAO (001) and LSAT (001) substrates. The observed resistance to epitaxial strain in SRO can be related to the rigid orthogonal network of the RuO6 octahedrons and the large elastic constants in bulk.
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Synthesis and Characterization of LiNbO3 Nanostructures.
Debasish Mohanty 1 , Girija Chaubey 1 , Amin Yourdkhani 1 , Gabriel Caruntu 1 , John Wiley 1
1 Department of Chemistry and Advanced Materials Research Institute, University of New Orleans, New Orleans, Louisiana, United States
Show AbstractFor the past several decades there has been considerable interest in the study of nanoscale distorted perovskite materials. Chemical precursor routes have become an excellent technique for the synthesis of high-purity multi-component nanoscale oxides because of their inherent qualities such as good homogeneity, compositional control, and lower processing temperatures. In this study, LiNbO3 nanocubes with an average edge length of 60 nm were synthesized using the single source precursor, LiNb(O-et)6 in a solvothermal method. By altering the precursors, reaction time and reaction temperature, hollow spheres of LiNbO3could also be produced. Piezoresponse force microscopy (PFM) was used to study the behavior of both nanocube and hollow sphere materials. Synthetic details and the structure-property-relationships of these LiNbO3 nanostructures will be presented. Further, these ferroelectric LiNbO3 nanostructures will be employed as a ferroelectric component to fabricate the multiferroic nanocomposites using magnetic nanostructures. The details of fabrication and characterization of these nanocomposites will also be presented.
9:00 PM - WW11.35
Tuning of Magnetic Properties in Cobalt-doped Nanocrystalline Bismuth Ferrite.
Gina Montes 1 , Oscar Perales Perez 2 , Marco Galvez 3 , Boris Renteria 1
1 Mechanical Engineering, University of Puerto Rico At Mayaguez, Mayaguez, Puerto Rico, United States, 2 Engineering Science and Materials, University of Puerto Rico, Mayaguez, Puerto Rico, United States, 3 Physics, University of Puerto Rico, Mayaguez, Puerto Rico, United States
Show AbstractFerromagnetism, ferroelectricity and ferroelasticity exhibited by bismuth ferrite BiFeO3 enable this material to be considered in the development of sensors, massive memory storage system or new devices based on the simultaneous use of the electron charge and spin. The present research is focused on the systematic study of the polyol synthesis of substrate-less nanocrystalline BiFeO3 particles and its structural and magnetic characterization. Synthesis under stoichiometric excess of bismuth species and the incorporation of cobalt ions in the ferrite lattice, coupled with the suitable selection of the thermal treatment conditions, allowed a fine tuning of the structural and magnetic properties of nancrystalline powders. Well-crystallized Bi1-xCoxFeO3 powders (x: 0.05-0.1 at%) were produced after annealing the precursors for one hour at 700οC. The corresponding average crystallite size was around 22 nm. Excess of Bi (5%-10%) promoted the complete crystallization of the ferrite powders, i.e., no precursor phases co-existed with the ferrite . In turn, both the saturation magnetization and coercivity of the powders were strongly influenced by the Cobalt concentration. These magnetic parameters varied from 2.70 emu/g and 19.57 Oe up to 5.70 emu/g and 1219 Oe for pure and 10 at.% Co-doped ferrite, respectively
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Crystal Structure and Multiferroic Properties of Bi0.5Sr0.5FeO3−δ.
K. Balamurugan 1 2 , N. Harish Kumar 1 , P. Woodward 3 , Maxim Avdeev 4 , Santhosh Nagappan Nair 1
1 Physics, Indian Institute of Technology Madras, Chennai, Tamilnadu, India, 2 Department of Chemistry and Biochemistry, Duquesne University, Pittsburgh, Pennsylvania, United States, 3 Department of Chemistry, Ohio State University, Columbus, Ohio, United States, 4 The Bragg Institute, Australian Nuclear Science and Technology Organization, Lucas Heights, New South Wales, Australia
Show AbstractThe polycrystalline Sr-substituted bismuth ferrite, Bi0.5Sr0.5FeO3−δ was synthesized by solid state reaction method and its magnetic and ferroelectric properties were investigated. Using X-ray diffraction (XRD) pattern, the crystal structure was determined by Rietveld refinement techniques. The XRD pattern of the sample was more or less equally fitted well using a cubic (Fm3m), orthorhombic (Pbnm) and rhombohedral (R3c) crystal structures. In accordance to the requirement of noncentrosymmetric structure imposed on the (magnetic) ferroelectrics by Neumann’s principle, the rhombohedral crystal system with the space group R3c is validated as the right structure to represent Bi0.5Sr0.5FeO3−δ. The corresponding refined lattice constants, in the hexagonal axes settings, are a = 5.5795(9) Å and c = 13.6655(5) Å. The magnetic measurements performed using a physical property measurement system (PPMS) showed clear hysteresis loops at 300, 200, 100 and 50 K. But, the magnetization does not exhibit any tendency to saturate even by applying a field of 7 T at 50 K. Further, the temperature dependency of magnetization showed a typical magnetic Curie transition above 350 K. Ferroelectric behavior of the sample is supported by a dielectric anomaly obtained around 675 K which corresponds to a typical ferroelectric to paraelectric transition. The ferroelectric property of Bi0.5Sr0.5FeO3−δ is understood to originate from the spontaneous ordering of the 6s2 lone pair electrons of Bi3+ ions. A systematic investigation was carried out, using neutron powder diffraction (NPD), Mössbauer spectroscopy and X-ray photoelectron spectroscopy (XPS) data, to determine the origin of the magnetic hysteresis observed at room temperature.
9:00 PM - WW11.37
Preparation of BiFeO3 Thin Film by Pulsed Laser Deposition under Magnetic Field.
Jung Min Park 2 , Fumiya Gotoda 2 , Seiji Nakashima 3 , Takeshi Kanashima 2 , Masanori Okuyama 1
2 Graduate School of Engineering Science, Osaka University, Toyonaka Japan, 3 Graduate School of Engineering, University of Hyogo, Himeji Japan, 1 Institute for Nanoscience Design, Osaka University, Toyonaka Japan
Show AbstractBiFeO3 (BFO) has attracted much attention as a multiferroic material, and its thin film shows giant ferroelectric polarization (Pr ~ 152 μC/cm2) at 80K. However, the insulation property is rather poor and has low magnetic hysteresis according to canting of spins. Therefore, improvement of the deposition method is required to obtain good insulation and magnetic properties. Here, when magnetic field is applied to evaporated species in the deposition chamber, moving directions of the species tend to be aligned along with the magnetic field by Lorentz force and chemical reaction of the species might be enhanced on the substrate. In this presentation, we have tried to prepare the BiFeO3 thin films by pulsed laser deposition using ArF excimer laser under magnetic field, and investigated crystallographic and dielectric properties. Magnetic field of 0-0.4T was applied in the vacuum chamber by a cylinder magnet cooled down by liquid nitrogen. The magnet consists of solenoid coil of oxide-superconductive tape immersed in liquid nitrogen container whose inner diameter, outer diameter and length are 70, 280 and 83 mm, respectively. Magnetic field is normal to the substrate and target. BFO thin films were deposited on Pt /TiO2 /SiO2 /Si at 550degree centigrade in oxygen of 0.05 and 0.1 Torr by this deposition apparatus. Deposition rate is about 6nm/min for the film prepared without magnetic field, but is enhanced 3 times larger for the film prepared at 0.4T. X-ray diffraction shows that the BFO thin films prepared without magnetic field is rhombohedral perovskite structure, and oriented preferentially to (110) and (111). The BFO films deposited under magnetic fields are oriented preferentially to (010) and (110). (010) diffraction peak shifts to lower angle by increasing magnetic field and lattice parameter normal to the film becomes larger. Ferroelectric hysteresis has been successfully obtained in the BFO thin film prepared with and without magnetic field. The film deposited under magnetic field gives better polarization saturation than the film prepared without magnetic field. From ferroelectric P-E hysteresis measurements, remanent polarization are 85.5 uC/cm2 for the film prepared without magnetic field and 42uC/cm2 for the film with magnetic field.
9:00 PM - WW11.38
Atomic-scale Structure of Nanosized BaTiO3 and BiFeO3 by Hhigh-energy XRD and Atomic Pair Distribution Functions Analysis.
Valeri Petkov 1
1 Physics, CMU, Mt.Pleasant, Michigan, United States
Show AbstractWith new technologies moving quickly towards smaller scales nanosized ferroelectric and multiferroic materials are produced in increasing numbers. Due to quantum size confinement effects, however, materials structured at the nanoscale exhibit extra structural distortions that can break the periodicity of their atomic-scale structure and make it substantially different from that occurring in the respective bulk materials. As a result nanosized materials, including nanosized ferroelectrics and multiferroics, may show properties that are very different from those exhibited by their bulk counterparts. We will present results from recent structure studies on free standing BaTiO3 [1] and BiFeO3 [2] particles with sizes varying from a few microns down to a few nm. The studies involve a combination of high-energy x-ray diffraction and atomic pair distribution functions analysis [3]. The observed strong correlation between the dimension, shape, structural distortions and properties of nanosized BaTiO3 and BiFeO3 will be discussed as well. 1.V. Petkov, V. Buscaglia, M. Buscaglia, Z. Zhao and Y. Ren “Structural Coherence and Ferroelectricity Decay in Submicron Sized Perovskites”, B 78 (2008) 054107.2. V. Petkov, S. M. Selbach, M.-A. Einarsrud, T. Grande and S. D. Shastri, “Melting of Bi-sublattice in nanosized BiFeO3 perovskite by resonant x-ray diffraction” , Phys. Rev. Lett. (November, 2010), in press.3. V. Petkov ” Atomic-scale structure of nanocrystalline materials by high-energy XRD”, Journal Cover Story : Materials Today 11 (2008) 28.
9:00 PM - WW11.39
Spin-charge-lattice Coupling Near 25 K in BiFeO3 Ceramics.
Ramachandran Balakrishnan 1 , Ambesh Dixit 2 , Ratna Naik 2 , Gavin Lawes 2 , Mamidanna Rao 1
1 Department of Physics, Indian Institute of Technology, Chennai, TamilNadu, India, 2 Department of Physics and Astronomy, Wayne State University, Detroit, Michigan, United States
Show AbstractInvestigations of low temperature Raman spectroscopy, dielectric, and magnetodielectric studies of as-prepared and vacuum annealed BiFeO3 ceramics revealed two dielectric anomalies near 25 K and 281 K. Systematic studies were carried out to probe the anomaly near 25 K which exhibits clear frequency dependence and falls close to a previously observed magnetic transition [1]. The low temperature dielectric relaxation behavior yielded characteristic energy scales of ~30 meV and ~34 meV for the as-prepared and vacuum annealed sample, respectively. Raman spectra showed softening of the E(TO5) and A1(TO4) modes near 25 K, and the Raman shift in phonon frequencies is found to be broader in the vacuum annealed than in the as-prepared ceramic. We observe a linear magnetodielectric coupling in both samples at 25 K, which we attribute to magnetoelectric coupling. These experimental results suggest that coupling among spin, lattice, and dielectric properties persist at low temperatures in BiFeO3. Detailed results will be presented and discussed. References:1. B. Ramachandran and M.S. Ramachandra Rao, Appl. Phy. Lett. 95, 142505 (2009).
9:00 PM - WW11.4
Tuning Resistive Switching Behavior in La0.7Sr0.3MnO3 with n+-Si Nanotips Arrays.
Cheong Chong 1 4 , Daniel Hsu 2 , Jauyn Grace Lin 2 , Li-Chyong Chen 2 , Kuei-Hsien Chen 3 , Yang-Fang Chen 1
1 Physics, National Taiwan University, Taipei Taiwan, 4 Taiwan International Graduate Program, Nano Science and Technology Program, Academia Sinica, Taipei Taiwan, 2 Center for Condensed Matter Sciences, National Taiwan University, Taipei Taiwan, 3 Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei Taiwan
Show AbstractDuring the last decade, electric-pulse-induced resistive switching (EPIR) effect in manganese oxide compounds (manganites) has been investigated intensively due to their strong potential for next generation memory devices. However, most research mainly focus on insulating manganites such as Pr0.7Ca0.3MnO3. There are very few studies on this EPIR effect in La0.7Sr0.3MnO3 (LSMO), probably due to its metallic behavior at room temperature. Nevertheless, its great interested to find ways to improve the EPIR effect in LSMO because of its high Curie temperature, which making it a good candidate for room temperature operated multiple resistance switching devices. Here we report the integration of LSMO into a heavy n-type-doped Si nanotips (SiNTs) arrays template. Owing to their large field enhancement of the tip geometry, low power operated resistive switching memory devices based on this SiNTs arrays could be expected. We first prepared the SiNTs by electron cyclotron resonance plasma enhanced chemical vapor deposition and this followed by the LSMO deposition using pulsed laser deposition method. Our data shows a huge enhancement of the EPIR ratio that is six times larger than the planar structure counterpart. More interestingly, different switching mechanism is discovered in LSMO that coated on n+-SiNTs with different tip geometry (in terms of apex angle, density and length). Our finding not only provides the route to enhance the switching ratio in this metallic LSMO, but also the information to understand and control the switching behavior in this nanojunction.
9:00 PM - WW11.40
Magnetic and Dielectric Properties Study of Cobalt Ferrite Nanoparticles Synthesized by Co-precipitation Method.
Muvvala Krishna Surendra 1 , D. Kannan 1 , Mamidanna Rao 1
1 Physics, Indian Institute of Technology, Chennai, TamilNadu, India
Show AbstractCobalt ferrite (CoFe2O4) is a promising material for the production of permanent magnets, magnetic recording media, magnetic fluids and catalysts. Cobalt ferrite nanoparticles were prepared by Massart’s method [1]. The phase purity was confirmed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). From XRD, using Debye-Scherer formula, the crystallite size of different particles was found to vary from 12 to 40 nm. Transmission electron microscopy (TEM) showed that the particles were spherical in shape and uniform in size with a narrow size distribution. All peaks of XRD patterns could be attributed to a cubic spinel structure with the lattice constant a = 8.397 Å. The XPS analysis indicates that the samples are composed of iron (Fe), cobalt (Co) and oxygen (O), with corresponding binding energies of 780.3 eV (Co 2p3/2), 796.0 eV (Co 2p1/2), 710.5 eV (Fe 2p3/2), 724.3 eV (Fe 2p1/2) and 529.7 eV (O 1s) respectively. The valence states were found to be Co2+, Fe3+ and O2-. The analysis of the Co 2p, Fe 2p and O 1s peaks yielded Co: Fe and Fe: O atomic ratios close to 1:2 and 1:2, respectively, as expected for the stoichiometric composition of cobalt ferrite. Mössbauer spectra showed two sextets corresponds to A and B sites of inverse spinel structured CoFe2O4. A and B sites having the hyperfine field (Hf) values of 46.1 and 41.7 T respectively, δ values were found to be 0.20 mm/s relative to the metallic iron, which were consistent with high spin Fe3+ [2]. Raman spectrum of cobalt ferrite shows the presence of five peaks at 200, 315, 467, 624, and 688 cm-1, in agreement with five Raman active optical modes (A1g + 1Eg + 3F2g) characteristic of cubic inverse-spinel structure space group O7h (Fd-3m). Magnetic transport studies were carried out by using vibrating sample magnetometer (VSM). Room temperature saturation magnetization (Ms) was found to be varied from 50.1 to 56.9 emu.g-1. The observed Ms for nanoparticles was found to be lower than that of the bulk value of CoFe2O4 particles (Ms~ 80 emu.g-1), however it is about 60 % of Ms observed in bulk which could prove to be useful in magneto-optical devices and in biomedical applications like hyperthermia and targeted drug delivery. The dielectric properties of nanocrystalline CoFe2O4 nanoparticles were studied using impedence analyser (Agilent 4294A, USA). The real part of the dielectric constant (εr') for the 15 nm grain size sample is found to be an order of magnitude higher than that of bulk cobalt ferrite. The present study showed that the dielectric properties can be tailor-made to suit the requirement of a particular application by controlling the grain size and the cation distribution. Detailed results will be presented and discussed in the manuscript.References:[1]Massart R. (1981) IEEE TRANSACTIONS ON MAGNETICS, VOL. MAG-17, No.2.[2]H. N. Ok, K.S. Baek, H.S. Lee, C.S. Kim, Phys. Rev. B., 1990, 41, 62.
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Engineered Perovskite-based Artificial Biferroic Heterostructures.
Ayan Roy Chaudhuri 1 , S. Krupanidhi 2
1 , Max Planck Institute of Microstructure Physics, Halle (Saale) Germany, 2 Materials Research Centre, Indian Institute of Science, Bangalore, Karnataka, India
Show AbstractIn order to realize large room temperature (RT) magnetoelectric behaviour and to overcome the shortcomings of the intrinsic multiferroic (MF) materials, there is a surge of interest in fabricating artificial MFs. Fabrication of two phase or multiphase composites is an attractive approach due to the lower leakage current and superior poling properties of bilayers and multilayers of such composites. Despite the advantages they suffer from severe limitations including poor mechanical coupling between the layers due to non epitaxial nature of the interfaces, impurities as a result of interfacial diffusion or reaction under high sintering temperatures, and lack of scaling capabilities. On the other hand, dramatic enhancement of properties in epitaxial superlattices (SLs) of various materials compared to their bulk properties inspired the researchers worldwide to fabricate artificial magnetoelectric epitaxial heterostructures, where lattice strain can effect in coupling the ferroelectric (FE) and ferromagnetic (FM) order parameters. To fabricate these artificial MF heterostructures mixed valence manganites have been adopted by many research groups as the FM materials and BaTiO3, Ba1-xSrxTiO3, (1-x) Pb(Mg1/3Nb2/3)O3 – x PbTiO3 etc. have been used as the FE materials. In this work epitaxial bilayered thin films consisting of La0.6Sr0.4MnO3 (LSMO) and 0.7 Pb(Mg1/3Nb2/3)O3 – 0.3 PbTiO3 (PMN-PT) layers of relatively different thicknesses were fabricated on LaNiO3 coated LaAlO3 (100) single crystal substrates by pulsed laser ablation technique. The crystallinity, ferroelectric, ferromagnetic and magneto-dielectric properties have been studied for all the bilayered heterostructures. Their microstructural analysis suggested possible Stranski-Krastanov type of growth mechanism in the present case. Ferroelectric and ferromagnetic characteristics of these bilayered heterostructures over a wide range of temperatures confirmed their biferroic nature. The magnetization and ferroelectric polarization of the bilayered heterostructures were enhanced with increasing PMN-PT layer thickness owing to the effect of lattice strain. In addition, evolution of the ferroelectric and ferromagnetic properties of these heterostructures with changing the thicknesses of the PMN-PT and LSMO layers indicated possible influence of several effects such as space charge, depolarization field, domain wall pinning, spin disorder etc. on the observed properties. Dielectric properties of these heterostructures studied over a wide range of temperatures under different magnetic field strengths suggested a possible role of elastic strain mediated magnetoelectric coupling behind the observed magneto-dielectric effect in addition to the influence of rearrangement of the interfacial charge carriers under an applied magnetic field.
9:00 PM - WW11.42
The Effect of Patterned vs. Unpatterned Acoustic Bragg Reflector on Barium Strontium Titanate Solidly Mounted Resonator.
George Saddik 1 , Robert York 1
1 Electrical and Computer Engineering, University of California Santa Barbara, Santa Barbara, California, United States
Show AbstractThe electrostrictive property of thin-film strontium titanate (STO) and barium strontium titanate (BST) is manifested as a voltage-induced piezoelectricity. During the past few years several research groups have demonstrated a new-type of voltage-activated bulk acoustic wave resonators that exploit this effect using the thin film bulk acoustic wave resonator (TFBAR) and solidly mounted resonator (SMR) approach. The SMR structure employs a distributed Bragg reflector or acoustic “mirror” under the device to isolate it from the substrate. There are several mechanisms that can contribute to the degradation of device performance such as surface and interface roughness associated with the top and bottom interfaces between the BST layer and the electrodes, acoustic losses in the SMR layers, excitation of lateral modes, and the use of an unpatterned “blanket” acoustic Bragg reflector (ABR). Several publications mention that a blanket ABR will degrade the SMR performance and advise to pattern the ABR. However, they do not quantify this degradation.The intention of this contribution is to investigate the performance degradation of the BST SMR due to the use of a blanket ABR. Two BST SMRs were fabricated, with a blanket and patterned ABR, respectively. The ABR in both cases consisted of a 4-layer Pt/SiO2/Pt/SiO2 structure, which has been used in all our previous BST SMR devices. Both devices were measured using a Cascade Microtech probe station, GGB GSG probes, and an Agilent PNA vector network analyzer. The data was collected on both samples from 0 V to 40 V in 5 V steps. The quality factors of the device with a blanket and patterned ABR were 70-80, and 120, respectively. The data clearly shows a 50% improvement in the SMR quality factor between the sample with a blanket and patterned ABR. This significant improvement in the quality factor of the SMR can be attributed to the reduction of undesirable parasitic capacitance and resistance between the contacts and the buried Pt-mirror layer.
9:00 PM - WW11.43
Effect of Nanomesa Size on Piezoelectric Response of BiFeO3 Thin Films.
Wittawat Saenrang 1 , Matthew Gossen 1 , Seung Hyub Baek 1 , Chung Wung Bark 1 , Thomas Tybell 2 , Chang-Beom Eom 1
1 , University of Wisconsin- Madison, Madison, Wisconsin, United States, 2 , Norwegian University of Science and Technology, Trondheim Norway
Show AbstractMany multifunctional oxide materials exhibit interesting piezoelectric, magnetoelectric and ferroelectric properties. Multiferroic BiFeO3 has been extensively studied due to its intriguing multifunctionality. Due to the strong magnetoelectric coupling between antiferromagnetism and ferroelectricity at room temperature, it has been considered as a promising candidate for new magnetoelectric devices. Also, BiFeO3, with the largest spontaneous polarization (Pr ~ 100 μC/cm2) have potential for high-density non-volatile memory devices. Moreover, the recently established strain-induced morphotrophic phase boundary indicates a potential for application of BiFeO3 in electromechanical devices. However, the piezoelectric properties of BiFeO3 thin films are expected to depend on mechanical boundary conditions and lateral size of the piezoelectric element.Here, we report the piezoelectric response of BiFeO3 thin films deposited, by radio frequency magnetron sputtering, on SrRuO3/SrTiO3 nanomesas having different sizes. The metallic SrRuO3 thin films were deposited on SrTiO3 substrates by pulsed laser deposition. Subsequently a set of nanomesa templates with lateral size ranging from 50 to 500 nm were defined in the SrRuO3/SrTiO3 by using a top-down lithography approach based on scanning tunneling microscopy. BiFeO3 thin films were then deposited on top of the nanomesa templates. Thereafter, the domain structure and the piezoelectric response were measured by piezoelectric force microscopy. Our work will help to utilize the piezoelectricity of BiFeO3 thin films in prospective nanoelectromechanical devices, as well as to understand fundamental physics of size-dependent piezoelectricity.
9:00 PM - WW11.44
Synthesis and Magnetic Properties of FePt@MnO Nano-hetero-Particles.
Thomas Schladt 1 2 , Tanja Graf 1 , Oskar Koehler 1 , Heiko Bauer 1 , Wolfgang Tremel 1
1 Institute for Inorganic and Analytical Chemistry, Johannes Gutenberg University Mainz, Mainz, RLP, Germany, 2 SpinAps, IBM Almaden Research Center, San Jose, California, United States
Show AbstractMonodisperse FePt@MnO nano-hetero-particles with different sizes and morphologies were prepared by a seed-mediated nucleation and growth technique. Both, size and morphology of the individual domains could be controlled by adjustment of the synthetic parameters. As a consequence, different particle constructs, including dimers, dumbbells and flowers, could be obtained by changing the polarity of the solvent. The FePt@MnO nano-hetero-particles were thoroughly characterized by (HR-)TEM- and XRD analysis and SQUID magnetometry. Due to a sufficient lattice match, the MnO NPs preferentially grow on the (111) surfaces of the fcc-FePt seeds. Furthermore, the surface spins of the antiferromagnetic MnO domains pin the magnetic moments of the ferromagnetic FePt NPs which leads to an exchanged biased magnetic hysteresis.
9:00 PM - WW11.45
Development and Characterization of Bismuth Ferrite-based Nanoceramics with a Core-shell Type Microstructure.
Li Sun 1 , Lin-feng Fei 1 , Helen L.W. Chan 1 , Y. Wang 1
1 Applied Physics, The Hong Kong Polytechnic University, Hong Kong SAR China
Show AbstractMultiferroic bismuth ferrite-based ceramics (BFO) which are featured with a core-shell type microstructure were prepared and characterized in this work. BFO ceramics prepared via conventional ceramic processes of ten exhibit relatively poor electric and magnetic properties as compared with BFO thin films and other materials. In particular, large leakage current, high coercive electric field, small ferroelectric polarization and magnetization are the major problems. To improve the electrical properties, the fabrication process was modified such that BFO ceramics with a core-shell type microstructure where BFO (with a grain size ~ tens nm) is the core and a thin layer of insulating metallic oxide (PZT etc) is the shell. With the shell to act as a barrier to electron and vacancy transportation, the leakage current of the material is significantly reduced. The BFO itself is doped with proper metallic element aiming to lower its leakage current and soften its ferroelectricity. With all these modifications, a large improvement in ferroelectric and magnetic properties and an enhanced coupling effect can be realized in the ceramics. Simulations were also conducted to investigate how such microstructure modification would affect the ME coupling of the material under external magnetic/electrical fields.
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Emergence of 90o Domain Walls in Multiferroic BiFeO3 Thin Film.
Jan-Chi Yang 1 , Chao-Hui Yeh 2 , Heng-Jui Liu 3 4 , Chun-Yen Peng 1 , Sheng-Chieh Liao 3 , Hsiang-Jung Chen 1 , Po-Wen Chiu 2 , Yi-Chun Chen 5 , Chih-Huang Lai 3 , Li Chang 1 , Ying-Hao Chu 1
1 Materials Science and Engineering, National Chiao Tung University, HsinChu Taiwan, 2 Institute of Electronics Engineering, National Tsing Hua University, HsinChu Taiwan, 3 Materials Science and Engineering, National Tsing Hua University, HsinChu Taiwan, 4 , National Synchrotron Radiation Research Center, HsinChu Taiwan, 5 Physics, National Chen Kung University, Tainan Taiwan
Show AbstractMultiferroic oxide systems have been a fascinating area for advanced condensed materials research since these materials offer the exciting potential for devices and applications that taking advantage of multiple order parameters. Room-temperature multiferroic BiFeO3 has played a key role in rejuvenating the field after a report of large ferroelectric polarization combined with both a high ferroelectric Curie temperature and a high antiferromagnetic Neel temperature. Inside this fascinating material, domain walls (DWs) of BiFeO3, which possess multifunctional electric and magnetic properties, are of great interests in future electronic devices. In previous study, room-temperature conductivity at ferroelectric DWs that are 180o and 109o have been observed. In this work, through epitaxial growth constraints, carefully-controlled BiFeO3 thin films are grown on NdScO3 single crystal substrate, which provide tensile strain on BiFeO3 thin films, and thus results in orthorhombic-like BiFeO3 and corresponding periodic 90o DWs. High-quality epitaxial BiFeO3 are grown by using pulsed laser deposition. X-ray reciprocal mapping and piezoresponse force microscopy has again confirmed the orthorhombic and 90o-like DW structure. Conducting behaviors on periodical 90o DWs are observed by conducting atomic force microscopy. Through atomic layer deposition and electron-beam lithography, natural formed 90o DW transport behaviors as a function of temperatures and magnetic fields have been probed to understand the fundamental properties of 90o DWs in BiFeO3. In addition, exchange bias studies and X-ray magnetic dichroism based spectromicroscopy have further revealed the fascinating magnetic properties in the tensile strained BiFeO3 DWs. Our results have shown that new type of DW could be created and stabilized through epitaxial strain. The 90o DW in orthorhombic-like BFO possesses unusual electronic and magnetic behaviors which are different from that in bulk of BiFeO3. Such results also show promising electrical properties for modern electronic devices and nanoelectronic applications which are based on multiferroic BiFeO3 DWs.
9:00 PM - WW11.48
Polarization Switching Behavior of Magnetoferroelectric YMnO3 Epitaxial Films at around the Magnetic Phase Transition Temperature.
Takeshi Yoshimura 1 , Kazuhiro Maeda 1 , Atsushi Ashida 1 , Norifumi Fujimura 1
1 Department of Physics and Electronics, Osaka Prefecture University, Sakai, Osaka, Japan
Show AbstractMultiferroic materials, which exhibit two or more ferroic features such as ferroelectric, are recently attracted much attention for cross-correlation between magnetic and electric properties. We are focusing on hexagonal rare-earth manganites RMnO3 (R= Ho, Er, Tm, Yb, Lu, Y, Sc, In) because it has unique features as magnetoferroelectrics. The spontaneous polarization of hexagonal RMnO3 is about 5 μC/cm2 and is directed along the sixfold z axis. Moreover, the spins of the six Mn3+ ions in the unit cell of hexagonal RMnO3 are ordered anitiferromagnetically in a triangular structure perpendicular to the polar axis below the Néel temperature (TN~60-80K). We have investigated the correlation between ferroelectric (FE) polarization switching and antiferromagnetic (AFM) ordering using YMnO3 and YbMnO3 epitaxial thin films. In YMnO3, Fiebig et al. reported that the FE domain wall is always accompanied by an AFM domain wall, while a single AFM domain wall can exist independently.[1] Therefore, it can be expected that the FE domain wall motion is influenced by AFM domain. (0001) YMnO3 epitaxial films were deposited using pulsed laser deposition method. Well saturated P-E hysteresis loops are observed from 280 to 10 K. The coercive electric field (EC) increases with decreasing temperature as shown in Fig. 1. It was also found that the frequency dependence of Ec is accorded with Ishibashi-Orihara's theory. In addition to these results, the FE domain wall motion is investigated using various characterizations including bias voltage dependence of dielectric constant, the time constant of the domain wall motion and Raman spectroscopy. It is suggested that the domain size and the velocity of domain wall motion increases with decreasing temperature and that domain wall motion is inhibited at around 120 K, which is higher than the TN of YMnO3.[1] M. Fiebig et al.: Nature vol. 419 (2002) 818.
9:00 PM - WW11.49
Nanoscale Ferroelectric, Magnetic and Surface Potential Behaviors of Multiferroic Copper-doped ZnO Using Scanning Probe Microscopy Technique.
Kaiyang Zeng 1 , Meng Fei Wong 1 , Tun Seng Herng 2 , Jun Ding 2
1 Mechanical Engineering, National University of Singapore, Nil Singapore, 2 Materials Science and Engineering, National University of Singapore, Nil Singapore
Show AbstractWide band gap semiconductors of ZnO have been of growing technological importance due to its versatile properties. Recent research has demonstrated that the substitution of transition-metal ions (such as Cu-ion) into the Zn sites leads to ferromagnetic ordering and ferroelectric behavior. In this study, pure ZnO film and Cu-doped ZnO (ZnO:Cu) films are fabricated with Pulsed Laser Deposition (PLD) method. Piezoresponse Force Microscopy (PFM), Magnetic Force Microscopy (MFM) and Kelvin Probe Force Microscopy (KPFM) techniques have been employed to investigate nanoscale ferroelectric, magnetic and surface potential behaviors of the ZnO:Cu films. Switching Spectroscopy PFM measurements show an inverse ferroelectric hysteresis loop within ±9.8 V, in which a negative bias increases the amplitude of the piezoresponse and vice versa. From this ferroelectric loop and localized poling effect, it is postulated that ZnO:Cu films may have a predominantly upward ferroelectric domains, which is in-phase with the negative bias. Furthermore, magnetic domains, ~1 – 2 μm in width, are successfully observed using the MFM technique. Finally, KPFM measurements show that ZnO:Cu films exhibit stable bipolar surface potential behavior at room temperature with an appropriate amount of Cu doping (~8 at.%), this phenomena is believed due to the existing of the oxygen vacancies can effectively trap the holes locally. All these findings unveil the potential of the ZnO:Cu film as a new transparent storage medium in memory and charge storage applications.
9:00 PM - WW11.5
Strain Effect on the Structure and the Electric Polarization of BiFeO3 and (SrTiO3)n(BiFeO3)n (n=2,4) Heterostructures.
Emilie Bruyer 1 , Adlane Sayede 1 , Rachel Desfeux 1
1 Unite de Catalyse et de Chimie du Solide - CNRS UMR 8181, Universite d'Artois, Lens France
Show AbstractWe report first principles calculations on strain effect on the structural properties and the electric polarization of BiFeO3 (BFO) and (SrTiO3)n(BiFeO3)n heterostructures. The calculations were done using the generalized gradient approximation (GGA) within the projected augmented wave method, as implemented in the Vienna Ab initio Simulation Package (VASP) code.Several symmetries, i.e. rhombohedral (R3c) and monoclinic (Cc, Pm and Pc), have been taken into account for the BFO structures under strain ranging from -1% to 6%. The studied (SrTiO3)n(BiFeO3)n heterostructures were constructed as an alternation of BFO and SrTiO3 (STO) unit cells along the [001] direction. All studied structures were assumed to exhibit a G-type antiferromagnetic ordering.Our first results reveal that BFO with moderate compressive strain adopts the Cc symmetry, as reported by previous LDA+U calculations [1]. For the (SrTiO3)n(BiFeO3)n heterostructures, it is found that the in-plane lattice constant takes an intermediate value between the equilibrium lattice constants of SrTiO3 and BiFeO3. Moreover, we observed an elongation of each superlattice along the c axis, due to a pronounced deformation of the layers at the interface STO/BFO, while outer layers undergo a slight compression along the c axis. Consequently, the spontaneous polarization is expected to increase mainly along the [001] direction. Reference:[1] A.J. Hatt, N.A. Spaldin, C. Ederer, Phys. Rev. B 81 (2010), 054109
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Ferroelectric Polarization and Domain Structure in Tetragonal Phase BFO Thin Film.
Jinxing Zhang 1 , R. Ramesh 2
1 Physics and Materials Science, University of California, Berkeley, Berkeley, California, United States, 2 Physics, UC Berkeley, Berkeley, California, United States
Show AbstractEpitaxial strain can be used to stabilize the mixture of tetragonal- and rhombohedral-like phases in BiFeO3 crystals. Higher strain can give rise to pure tetragonal-like phases, which is predicted to be a ferroelectrics with a large polarization of ~150 µC/cm2. A rotation of ferroelectric polarization from tetragonal-like phase to rhombohedral-like phase has also been predicted. In this abstract, a high ferroelectric polarization of 125 µC/cm2 has been observed in the tetragonal-like BFO thin films. Piezoresponse force microscopy images and x-ray diffraction patterns reveal its monoclinic nature on this super-tetragonal structure. The origin and dynamics of the large polarization and nanoscale polarization switching in BiFeO3 film with a mixture of rhombohedral- and tetragonal-like symmetries have been explored based on the understanding of its ferroelectric domain configuration. Here we propose a rotation of ferroelectric polarized vectors from phase to phase by re-constructing the polarization across the phase boundaries within 10 to 15 unit cells. Detailed electric-field-driven switching path unveils the mechanism behind the ultrahigh electromechanical coupling effect, which can be introduced into the explorations of large ferroelectric polarization in other ferroelectrics. This work also provides insights into engineering ferroelectrics for the future ferroelectric storage devices.
9:00 PM - WW11.51
Multiferroic Properties of Nano-structured Pb(Zr,Ti)Ox-CoFe2O4 Hybrid Material.
Feng Zhang 1 , Jea Cho 1 , Thomas Quicke 2 , Ya-Chuan Perng 1 , Sarah Tolbert 2 , Jane Chang 1
1 Chemical and Biomolecular Engineering, UCLA, Los Angeles, California, United States, 2 Chemistry and Biochemistry, UCLA, Los Angeles, California, United States
Show AbstractHybrid multiferroic materials have attracted much attention due to their interesting multifunctional properties and potential applications in next generation of memory devices. Bilayered multiferroic Pb(Zr,Ti)O3/CoFe2O4 (PZT/CFO) thin films were proved to have good magnetoelectric (ME) effect, thus it is promising to motivate the investigation of three-dimensional and nano-scaled PZT/CFO architecture to increase memory density and optimize multiferroic properties. Mesoporous CFO thin films were formed by evaporation-induced self-assembly with pores of 14 nm in diameter and exhibited ferromagnetism with saturation magnetization of 9×10-4 emu and coercivity of 1200 Oe at room temperature. Ultra-thin PZT films were synthesized by atomic layer deposition with a deposition rate of 0.7 nm/cycle and a 14-nm thick film presented remanent and saturation polarization of 4.3 and 7.9 μC/cm2, and a coercive electrical field (Ec) of 1.26 MV/cm. Combining the porous CFO with a uniform and conformal coating of 5-7 nm PZT films, a nano-structured PZT-CFO hybrid material was formed and confirmed by scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS) measurements. To assess multiferroic properties of the PZT/CFO composite, superconducting quantum interference device (SQUID) magnetometer was used. When the samples were measured in-plane, the saturation magnetization was relatively constant at 7.8×10-4 emu after electrical poling at 1kV/cm. While the samples were measured out-of-plane, the saturation magnetization decreased from 9.0×10-4 to 8.5×10-4 emu after identical electrical poling. Polarization voltage (P-V) measurement is underway and so far the promising results indicate ALD enables the synthesis of a PZT-CFO composite with magnetoelectric coupling effect and potential in memory applications.
9:00 PM - WW11.52
Excimer Laser Annealing of Piezoelectric Thin Films for MEMS Applications.
Bharadwaja Srowthi 1 , Susan Trolier-McKinstry 1
1 Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania, United States
Show AbstractFerroelectric materials have a wide range of applications such as nonvolatile memories, pyroelectric detectors, miniaturized piezoelectric transducers and tunable microwave devices. However, the crystallization temperatures of ferroelectric thin films are often ≥ 600 oC to obtain better functional properties. Lowering the crystallization temperatures of ferroelectric/piezoelectric thin films should enable integration with CMOS circuits as well as on temperature sensitive substrates such as polymers. In this presentation, the crystallization kinetics in laser annealed Pb(Zr0.52,Ti0.48)O3 (PZT) and BaTiO3 thin films on different substrates will be discussed. A KrF excimer laser having a ~20-25 ns pulse width and an energy density ~40-60 mJ/cm2 was used to crystallize the films at substrate temperatures below 400 oC. The orientations of the films were controlled via a bottom template layer at the film substrate interface; {111} and {100} orientations were achieved on (111) Pt and {001} PbTiO3 surfaces, respectively. Laser annealed {001} and {111} oriented PZT thin films exhibited dielectric permittivity and loss tangents of 1000, 0.05 and 1100, 0.04 respectively. The remanent polarization for {001} and {111} samples are 33 μC/cm2 and 21 μC/cm2 respectively, with corresponding e31,f values of ~ -9 C/m2 and -8 C/m2. Furthermore, laser assisted crystallization of ~ 200-300 nm thick PZT layers on (111) Pt-coated polyimide (Kapton) substrates exhibited dielectric and ferroelectric properties comparable to laser annealed PZT films on platinized silicon substrates. In addition, the structural and electrical properties of laser annealed PZT thin films on polymers will be discussed for possible energy harvesting and flexible electronics applications. For both Pb-based and non Pb-based electroceramic thin films, the crystallization kinetics via laser annealing are nucleation limited. This will be discussed within the framework of rate dependent Avrami theory.
9:00 PM - WW11.53
The Size-dependent Ferroelectric Phase Transition in BaTiO3 Nanocrystals Probed by Surface Plasmons.
Daniel Szwarcman 1 , Daniel Vestler 1 , Gil Markovich 1
1 School of Chemistry, Tel-Aviv University, Tel-Aviv Israel
Show AbstractUnderstanding the fundamental aspects of nanoscale ferroelectricity is important for various applications of ferroelectrics, such as non-volatile memories, pyroelectric and piezoelectric devices. At the nanoscsale, in particular at nanocrystals (NCs) that are strongly confined, deviations from “bulk” properties are expected due to stronger depolarization fields. This leads to the idea of a critical correlation volume below which ferrolelectricity cannot be sustained. Reports of the size dependent phase transition properties encompass a broad range of results and suggest a drop in Curie temperature with decreasing size. As NC size decreases and the surface layer takes a substantial part of the volume an average over surface and interior would be measured using techniques such as XRD and Raman scattering. Thus, in order to probe the phase transition at the nanoscale, a different method selectively sensitive to the surface of the ferroelectric NCs should be used.A technique for probing the temperature dependence of the dielectric constant of ferroelectric NCs using shifts in the localized surface plasmon resonance wavelength of gold nanoparticles attached to the surface of the ferroelectric NCs is demonstrated. We study the ferroelectric-to-paraelectric phase transition of Barium Titanate (BTO) nanocubes in three size regimes. Temperature-dependent Raman spectroscopy was applied to probe the whole volume of the NCs. It was revealed that ~16nm BTO NCs were dominated by surface effects, and as the NC size increased bulk BTO behavior governed. This work strengthens the concept of having different surface and interior, bulk-like contributions to the ferroelectricity and to the phase transitions. It thus indicates on the absence of an intrinsic size-dependence of the transition temperature. In addition the surface ferroelectricity behaves differently from the bulk-like ferroelectricity and is characterized by long relaxation time scales.
9:00 PM - WW11.54
Influence of Crystal System on Ferroelectric Properties of (001) BiFeO3 Epitaxial Thin Films.
Katsuya Ujimoto 1 , Takeshi Yoshimura 1 , Atsushi Ashida 1 , Norifumi Fujimura 1
1 Graduate School of Engineering, Osaka Prefecture University, Sakai, Osaka, Japan
Show Abstract Lead-free ferroelectric BiFeO3 is one of the promising materials for piezoelectric devices because BiFeO3 has a huge spontaneous polarization as large as ~100 μC/cm2 and high Curie temperature (TC; 850 °C). There are various attempts to engineer the properties of BiFeO3. For engineering the piezoelectric property, it is important to explore morphotropic phase boundary (MPB) composition and to control crystallographic structure [1]. There are lots of reports about engineering the crystal structure and ferroelectric properties of BiFeO3 thin films by substitution. While crystal system of BiFeO3 is rhombohedral in bulk, it becomes tetragonal or monoclinic in film form in many cases due to the restriction of the substrate clamping. Therefore, it is important to reveal the effect of substrate clamping on the crystal system and ferroelectric properties of the films. In this paper, the lattice misfit is controlled by introducing the buffer layer. The effect of the misfit strain on the crystal system and the ferroelectric property of the films is investigated. BiFeO3, bottom electrode and buffer layer were deposited by pulsed laser deposition method. BaTiO3 epitaxial films were deposited on (001) SrTiO3 substrate as the buffer layer. Epitaxially grown SrRuO3 bottom electrode with 5-nm-thick was deposited on the buffer layer so that the lattice constant of SrRuO3 becomes equal to that of buffer layer by clamping. Finally, BiFeO3 epitaxial films were deposited at a growth temperature of 500 °C and an oxygen pressure of 1 mTorr. 900-nm-thick BiFeO3 films with and without buffer layer were fabricated. The structural analysis using reciprocal space mapping of X-ray diffraction indicates that the lattice misfit and crystal system of BiFeO3 film with and without the buffer layer is 0.5 %, rhombohedral and -1.3 %, monoclinic, respectively. In the electric field dependence of remanent polarization a significant difference was not recogniazed for both films. Furthermore, the electric permittivity of the rhombohedral film is 14 % larger than that of monoclinic film. On the other hand, it was found that the out of plane inverse piezoelectric response of the rhombohedral film is about 2 times larger than that of monoclinic film. Since the enhancement of piezoelectric response cannot be explain by intrinsic effect, it is suggested that the enhancement is caused by the effect of engineered domain.[1] S. -E. Park and T. R. Shrout, J. Appl. Phys., 82, 1804 (1997)
9:00 PM - WW11.55
Magnetic and Ferroelectric Properties of Sol-gel Derived NiFe2O4 and Pb(Zr0.52Ti0.48)O3 Thin Film Multilayer Composites on Silicon Substrates.
Safoura Seifikar 1 , Xiaotao Liu 1 , Frank Hunte 1 , Weston Straka 1 , Yaser Bastani 2 , Christopher Quintero 2 , Justin Schwartz 1 , Nazanin Bassiri-Gharb 2
1 Material Science and Engineering department, North Carolina State University, Raleigh, North Carolina, United States, 2 Mechanical Engineering Department, Georgia institute of technology, Atlanta, Georgia, United States
Show AbstractMagnetoelectric materials are a class of multifunctional materials that show the coupling interaction between ferroelectricity and ferromagnetism. This property is observed in single phase materials but is generally low and seen mostly at low temperature. Thus, heterostructure magnetoelectric composites have been developed based on coupling of piezoelectric and magnetic materials to obtain a large magnetoelectric response at room temperature. Through interfacial coupling, these materials show electrical polarization in an applied magnetic field, and conversely display a magnetostrictive response to an applied electrical field.In this study, magnetoelectric thin film multilayers are prepared successfully using NiFe2O4 as the magnetostrictive phase and Pb(Zr0.52Ti0.48)O3 as Piezoelectric phase via chemical solution processing. The phase formation and orientation is evaluated by XRD and the morphology and interface are characterized by electron microscopy. The ferroelectricity and magnetization of the composite are measured at room temperature. It is revealed that the composites exhibit well-defined ferroelectric hysteresis loop with saturation polarization and coercive field about 68 μC/cm2 and 35 kV/cm, respectively. The composite shows a magnetic coercive field of 120 Oe, which is significantly lower than pure nickel ferrite films, while saturation magnetization values are close and about 170 emu/cm3. In this study, the effect of magnetic field and annealing temperature on texture and properties of the piezoelectric and magnetostrictive layers are also discussed.
9:00 PM - WW11.57
Magnetic-field Tuning of Ferroelectric Piezoelectric Response in Magnetoelectric Core-shell Nanowires.
Stephanie Johnson 1 , Peter Finkel 2 , Stephen Nonnenmann 1 , Konrad Bussman 3 , Jonathan Spanier 1
1 Materials Science & Engineering, Drexel University, Philadelphia, Pennsylvania, United States, 2 Code 1512, Naval Undersea Warfare Center, Newport, Rhode Island, United States, 3 Code 6360, Naval Research Laboratory, Washington, District of Columbia, United States
Show AbstractWe present on the growth, structure, and functional property characterizations of core-shell magnetoelectric nanowires (NWs) with synthetic control of core and shell diameters. Each NW consists of a ferromagnetic metal core exhibiting high magnetostriction and a piezoelectric shell made of either multiferroic or ferroelectric oxides. The ferroelectric piezoelectric properties and the effects of finite shell thickness and curvature were investigated via static proximal probing as a function of applied DC magnetic field and bias electric field using a scanning probe microscope. The ferroelectric and related properties of the oxide components, including the ferroelectric hysteresis, coercive field, and the magnitude of piezoelectric response are all seen to depend sensitively on applied magnetic field. We find evidence for strong responses owing to magnetic field-induced magnetoelastic and magnetoelectric coupling. We will discuss the effects of varying core and shell diameters. Work supported by the ARO and by the ONR.
9:00 PM - WW11.7
Hydrogenated ROMP Copolymers as Novel High Temperature Dielectric Materials with Improved Processing Characteristics.
Shawn Dirk 1 , Leah Appelhans 1 , Kirsten Cicotte 1 , Ross Johnson 1
1 Organic Materials, Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractMuch research has focused on the development of new polymer thin film dielectric materials. A potential application for these materials is in capacitors for use in the inverters of next generation hybrid electric vehicles (HEVs). Capacitors used in HEVs inverters will be required to operate at 150 °C, 450V, and have an energy density of 0.2 J/cm3 or greater at 450 V. Polymer based thin film capacitors are ideal for this application due to their low cost and high dielectric breakdown field. In addition, thin polymer film-based capacitors exhibit a preferred failure mechanism known as graceful failure where the capacitor fails as an open rather than failing as a short, which could lead to potential fires or explosions. Polynorbornene formed via the ring opening metathesis reaction (ROMP) is a promising material as a polymer dielectric as it has high breakdown strength (~3000 kV/cm) and a reasonable dielectric constant (2.93); however, it has a limited operational temperature range when used as a capacitor dielectric. We have increased the operational temperature range by copolymerizing norbornene with N-phenyl-7-oxanorbornene-5,6-dicarboximide. The copolymerization served as a method to increasing the glass transition temperature and to increase the heteroatom content. Processing the copolymer material into thin films was difficult as the copolymers were thermal-set resins and needed to be solvent-cast rather than extruded. We hydrogenated a series of copolymers in order to convert the polymers to thermoplastics. The new hydrogenated materials with a large mole fraction of imide formed dielectrics with improved breakdown strengths and improved processing characteristics. The hydrogenated dielectrics enabled the formation of capacitors with improved high temperature performance at temperatures in excess of 150 °C. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.
9:00 PM - WW11.8
Dynamic Dielectric and Impedance Anomalies Near Magnetic Phase Transitions in Multiferroics.
Sandra Dussan 1 , Ashok Kumar 1 , Ram Katiyar 1
1 Physics and Institute for Functional Nanomaterials, University of Puerto Rico, San Juan United States
Show AbstractMagnetoelectric (ME) Multiferroics (MF) are attractive class of multifunctional materials that simultaneously exhibit more than two ferroic orders (i.e ferroelectric (FE), ferromagnetic (FM) and/or ferroelastic) and the additional coupling between them are of interest owing to their potential applications in devices, such as novel memory elements and magnetic- field sensors. Artificially designed Nanocapacitor superlattices were formed with 5nm/1nm and 7nm/1nm periodicity of ferroelectric (piezoelectric) PbZr0.52Ti0.48O3 (PZT) and half-metallic ferromagnetic La0.67Sr0.33MnO3 (LSMO) deposited onto 100-LaAlO3 (LAO) and (LSAT) substrates by pulsed laser deposition. θ-2θ x-ray scan and phi scan revealed epitaxial growth of nanocapacitors. At room temperature, the dielectric tunability was ~35 % at high frequencies with well saturated polarization whereas the local piezo force microscopy (PFM) measurements revealed switching of polarization under the external bias field. To gain further understanding of the electrical properties of the nanocapacitors, impedance spectroscopy, dielectric permittivity and ac conductivity were investigated. We observed dynamic magneto-resistive and magneto-dielectric effects near the LSMO metal-insulator and ferromagnetic phase transition temperature.
9:00 PM - WW11.9
Electron Diffraction Studies of Multiferroic BiMnO3-δ.
Alexander Eggeman 1 , Paul Midgley 1 , Anthony Cheetham 1 , Chintanami Rao 2
1 Materials Science, University of Cambridge, Cambridge United Kingdom, 2 International Centre for Materials Science, JNCASR, Bangalore India
Show AbstractElectron diffraction studies of several oxygen-deficient bismuth manganite structures are reported. One sample (with the lowest oxygen content) exhibits the accepted orthorhombic structure of bismuth manganite with the space group C2/c. The other samples exhibit different orthorhombic structures, the sample with the highest oxygen content crystallises into a large orthorhombic cell with approximate cell parameters 4ap x √2ap x 2√2ap and a likely space group Pmn21. The intermediate oxygen content seems to have formed two different structures, a majority phase with the conventional orthorhombic perovskite super-cell structure and a minority component that forms a n=2 Ruddlesden-Popper phase with space group Cmc21. The presence of non-centrosymmetric space-groups for the latter two structures allows the reported multiferroic properties of the samples to be explained.
Symposium Organizers
Patrycja Paruch University of Geneva
Mark Rzchowski University of Wisconsin-Madison
Evgeny Tsymbal University of Nebraska-Lincoln
Thomas Tybell Norwegian University of Science and Technology
WW13: Ferroelectric Thin Films and Improper Ferroelectrics
Session Chairs
Friday PM, April 29, 2011
Room 2018 (Moscone West)
2:30 PM - **WW13.1
First Principles Simulations on Insulating/Insulating and Insulating/Metal Oxide Interfaces.
Pablo Aguado-Puente 1 , Pablo Garcia-Fernandez 1 , Marcos Verissimo-Alves 1 , Javier Junquera 1
1 Ciencias de la Tierra y Física de la Materia Condensada, Universidad de Cantabria, Santander, Cantabria, Spain
Show AbstractFerroelectric perovskites are materials of great fundamental and applied interest. This family of materials displays a great range of functionalities, from ferroelectricity to superconductivity. More interestingly, perovskites show a very rich phase diagram allowing for a great tunability playing with doping, epitaxial strain, and the combination of different materials in heterostructures. This has led to the discovery of completely new interfaced-based phenomena in the last years, for instance (i) a fundamentally new type of ferroelectricity has been discovered in PbTiO3/SrTiO3 superlattices, due to the unexpected coupling of ferroelectric and antiferrodistortive structural distortions in these heterostructures1 or (ii) the discovery of metallic conduction at the n-type polar interface between LaAlO3 and SrTiO3, two excellent band insulators.2The work by Bousquet et al. focused on the monodomain configuration of the superlattices. However, a recent work3 has suggested that the ground state of this system might be actually polydomain for most periodicities. This work also points out that the small mismatch between PbTiO3 grown on SrTiO3 allows the growth of relatively thick enough superlattices making this a very suitable system for the study of domain structures in ultrathin films. In this talk we will report on our recent first-principles simulations on PbTiO3/SrTiO3 superlattices including the presence of domains to complement the last experimental results to better understand the properties of domain structures in these superlattices.We will also present our results on the possibility of generating a two dimensional electron gas at the p-type and n-type interfaces between a I-V oxide (such as KNbO3) and a II-IV oxide (such as BaTiO3), highlighting the importance that the lattice screening has on the formation of the 2DEG. [1] E. Bousquet, M. Dawber, N. Stucki, C. Lichtensteiger, P. Hermet, S. Gariglio, J.-M. Triscone, & Ph. Ghosez, Nature 452 , 732 (2008).[2] A. Ohtomo & H. Y. Hwang, Nature 427 , 423 (2004). [3] P. Zubko, N. Stucki, C. Lichtensteiger, & J. M. Triscone, Phys. Rev. Lett. 104 , 187601 (2010).
3:00 PM - WW13.2
Thickness Dependent Ferroelectric Properties of Ultrathin BaTiO3 Films.
David Felker 1 , H. Jang 3 , M. Rzchowski 1 , C. Eom 2
1 Physics, UW - Madison, Madison, Wisconsin, United States, 3 , Korea Institute of Science and Technology, Seoul Korea (the Republic of), 2 Materials Science and Engineering, UW - Madison, Madison, Wisconsin, United States
Show AbstractThe thickness dependence of the spontaneous polarization and coercive field of ultrathin epitaxial BaTiO3 with single crystal SrRuO3 electrodes on SrTiO3 substrates was studied. The heterostructures were grown by pulsed laser deposition with in-situ reflection high energy electron diffraction analysis. The BaTiO3 thickness ranged from 6 unit cells (uc) to 125 uc. Films as thin as 8 uc showed electric polarization hysteresis loops with clear spontaneous polarization. This is the thinnest BaTiO3 incorporated in a device structure for which ferroelectric properties have been demonstrated with a direct electrical measurement. We compare these results to a theoretical model where the polarization is reduced by a depolarizing field incompletely-screened by the SrRuO3 electrodes. Capacitance-electric field loops at low frequencies show hysteresis only for thicker BaTiO3 samples, suggesting that the remanent polarization goes to zero around 25 uc to 50 uc. In light of a nonzero spontaneous polarization extracted from the polarization vs electric field loop measurements, we conclude that BaTiO3 remains ferroelectric below 25 uc, but breaks into equal up and down domains with zero net polarization. This leads to a higher critical thickness for memory applications than strictly the critical thickness between the ferroelectric and paraelectric state. The coercive field increases with decreasing thickness in the entire range studied. The temperature dependence of the ferroelectric properties is investigated down to 77 K.
3:15 PM - WW13.3
Polarization Instability in Ultrathin BaTiO3 Capacitors.
Haidong Lu 1 , D. Wu 1 , P. Lukashev 1 , X. Liu 1 , J. Burton 1 , A. Stamm 1 , C. Bark 2 , C. Folkman 2 , D. Felker 3 , M. Rzchowski 3 , C. Eom 2 , E. Tsymbal 1 , A. Gruverman 1
1 Department of Physics and Astronomy, University of Nebraska-Lincoln, Lincoln, Nebraska, United States, 2 Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States, 3 Department of Physics, University of Wisconsin-Madison, Madison, Wisconsin, United States
Show AbstractMaintaining and controlling a stable electrical polarization at room temperature in ferroelectric perovskite oxide thin films is essential for exploiting the functionality of these materials for nanoscale applications. We report on the investigation of polarization relaxation in high-quality single-crystalline ultrathin (in the range from 2 to 20 nm) BaTiO3 capacitors by means of piezoresponse force microscopy (PFM) and pulsed switching current measurements (PUND). It is shown that although polarization is stable in ultrathin BaTiO3 films with no top electrodes, deposition of top electrodes (SrRuO3 or La0.7Sr0.3MnO3) results in severe polarization relaxation. This effect is a consequence of strong effective depolarizing fields due to unfavorable interface terminations with the deposited electrodes, as opposed to more complete screening in the films by adsorbed charges on the free surface. These interface effects can smear out the ferroelectric transition and can even make the ferroelectricity unstable at room temperature. Several approaches to enhance polarization retention in the case of a deposited electrode, including strain engineering and control of electrically boundary conditions, were explored. In particular, first-principle calculations based on density functional theory show that engineering of the atomic termination at the electrode interface with BaTiO3 by insertion of ultrathin dielectric layers of SrTiO3 can alleviate stability issues in the case of SrRuO3 electrodes. This approach is confirmed by PFM observations showing spatially resolved dynamics of relaxation, local PFM spectroscopy and determination of the characteristic relaxation times by PUND.
3:30 PM - WW13.4
Critical Thickness of Ferroelectric Thin Films Controlled by Polar Interfaces.
Yong Wang 1 , Manish Niranjan 1 , Karolina Janicka 1 , Julian Velev 2 , Mikhail Zhuravlev 3 , Sitaram Jaswal 1 , Evgeny Tsymbal 1
1 Department of Physics and Astronomy, University of Nebraska-Lincoln, Lincoln, Nebraska, United States, 2 Department of Physics, University of Puerto Rico, San Juan, Puerto Rico, United States, 3 Kurnakov Institute for General and Inorganic Chemistry, Russian Academy of Sciences, Moscow Russian Federation
Show AbstractTo increase the capacity of the storage media and open possibilities for novel functional nanoscale structures, such as ferroelectric and multiferroic tunnel junctions [1] and switchable two-dimensional electron gases, [2] it is essential to bring ferroelectricity into the nanometer scale. Ferroelectric stability of thin films placed between two metal electrodes is affected by a number of factors, such as the screening associated with free charges in metals, [3] ionic screening in oxide electrodes, [4]and intrinsic dipole moments at the interfaces. [5] Here based on first-principles and model calculations we investigate the effect of polar interfaces on the ferroelectric stability of thin-film ferroelectrics. [6] We consider Vacuum/LaO/BaTiO3/LaO, LaO/BaTiO3, and SrRuO3/LaO/BaTiO3/LaO heterostructures as representative systems, where a LaO monolayer at the interface with a TiO2-terminated BaTiO3 produces a polar interface. We find that the polar interfaces create an intrinsic electric field that is screened by the electron charge leaking into the BaTiO3 layer. The amount of the leaking charge is controlled by the boundary conditions which are different for the three heterostructures considered. The intrinsic electric field forces ionic displacements in BaTiO3 to produce the electric polarization directed into the interior of the BaTiO3 layer. This creates a ferroelectric dead layer near the interfaces that is non-switchable and thus detrimental to ferroelectricity. The effect is stronger for a larger effective ionic charge at the interface and longer screening length due to a stronger intrinsic electric field that penetrates deeper into the ferroelectric. The predicted mechanism for a ferroelectric dead layer at the interface controls the critical thickness for ferroelectricity in systems with polar interfaces. References:1. E. Y. Tsymbal and H. Kohlstedt, Science 313, 181 (2006).2. M. K. Niranjan et al., Phys. Rev. Lett. 103, 016804 (2009). 3. R. R. Mehta et al., J. Appl. Phys. 44, 3379 (1973).4. G. Gerra et al., Phys. Rev. Lett. 96, 107603 (2006).5. C.-G. Duan et al, Nano Lett. 6, 483 (2006).6. Y. Wang et al., Phys. Rev. B. 82, 094114 (2010).
3:45 PM - WW13.5
Electrical Properties of Improper Ferroelectrics.
Massimiliano Stengel 1 , Craig Fennie 2
1 , ICMAB (CSIC), Bellaterra Spain, 2 , Cornell University, Ithaca, New York, United States
Show AbstractIn many ferroelectric materials and superlattices, the macroscopic polarization interactsnontrivially with additional structural order parameters. In perovskite oxides and hexagonalmanganites these are often related to rotations and tilts of the oxygen polyhedra surroundingthe B-site cation. In some cases, the nature of the coupling is such that the polarizationappears as a secondary effect, whereas the structural degrees of freedom act as primary orderparameters in the phase transition. These materials are called "improper" ferroelectrics,as opposed to the "proper" ones like, e.g., BaTiO3 or PbTiO3.Improper ferroelectrics are characterized by unusual features that are very interesting,both from the point of view of the fundamental physics and in sight of potential deviceapplications. This is particularly true in the context of multiferroics research, wherethese materials are playing an increasingly central role. A major limiting factor to practicaluse of improper ferroelectrics of any type, however, are their relative scarcity and materialdesign rules have remained elusive. As a result discovery of new improper ferroelectricsoccurs serendipitously.First-principles calculations have proven to be a valuable tool to understand the relevantdegrees of freedom and mutual couplings in this class of materials, and to use this knowledgeto design new compounds with tailored properties. While powerful, this kind of studies can berelatively cumbersome, especially in compounds with lower symmetry which are characterizedby a large number of active degrees of freedom at the microscopic level. A general theoreticaltool that would allow us, solely on the basis of the macroscopic electrical properties, to clearlyidentify whether an arbitrary compound is likely to display an improper ferroelectric behavior,would be a clear advantage in this context.In this talk, I will discuss how the recently developed methods to control the macroscopicelectric displacement in periodic ab-initio calculations can naturally provide such a test.In particular, I will show that unambiguous features in the electrical diagram provide asolid theoretical means to clearly distinguish the electrical properties of improperstructural ferroelectrics from those of proper ferroelectrics such as BaTiO3.I will illustrate these ideas by using YMnO3 and PbTiO3/SrTiO3 superlattices asprototypical test cases.
4:30 PM - WW13.6
WITHDRAWN 4/29/11 Ca3Mn2O7: A `Hybrid’ Improper Ferroelectric in which Oxygen Rotations are Predicted to Enable Electrically-poleable Magnets: Part 2--Experiment.
Carolina Adamo 1 , Rajiv Misra 2 , Nicole Benedek 4 , Sava Denev 3 , A. SenGupta 3 , Julia Mundy 4 , June Lee 1 , David Muller 4 , Venkat Gopalan 3 , Craig Fennie 4 , Peter Schiffer 2 , Darrell Schlom 1
1 Department of Materials Science and Engineering, Cornell University, Ithaca, New York, United States, 2 Department of Physics and Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania, United States, 4 School of Applied and Engineering Physics, Cornell University, Ithaca, New York, United States, 3 Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania, United States
Show AbstractBenedek and Fennie[1] recently identified a new mechanism involving octahedral rotations enabling an applied electric field to globally and deterministically switch the magnetization by 180 degrees in a single-phase multiferroic material. An embodiment of this mechanism identified by their first-principles calculations is Ca3Mn2O7, an n=2 Ruddlesden-Popper phase. To test their predictions we report relevant properties of epitaxial Ca3Mn2O7 thin films. 50 nm thick unstrained Ca3Mn2O7 films were grown by reactive molecular-beam epitaxy on (110) YAlO3 single crystal substrates using a shuttered growth technique where the shuttering is used to deposit the constituent monolayers in the same order as the layering along the c-axis of Ca3Mn2O7. The phase purity and crystallinity of the films was monitored during growth by reflection high-energy electron diffraction and after growth by four-circle x-ray diffraction (XRD). XRD reveals that the Ca3Mn2O7 films are single phase and epitaxial with (001) Ca3Mn2O7 // (110) YAlO3. The out-of-plane lattice spacing is c=1.94+/-0.01 nm. The magnetic properties show a Neél transition temperature of T = 120K, similar to the bulkmaterial.[2] Second harmonic generation measurements show that a weak polar order exists at room temperature and it persists until ~700 degrees C.[1] N. A. Benedek and C. J. Fennie, arXiv:1007.1003v1.[2] J. B. MacChesney, H. J. Williams, H. F. Potter, and R.C. Sherwood, Phys. Rev 164, 2 (1967).
4:45 PM - WW13.7
Strain-induced Ferromagnetism in Epitaxial LaCoO3 on Si (100).
Agham Posadas 1 , Morgann Berg 1 , Hosung Seo 1 , David Smith 2 , Alexander Kirk 3 , Dmitry Zhernokletov 3 , Robert Wallace 3 , Alex de Lozanne 1 , Alexander Demkov 1
1 Physics, University of Texas at Austin, Austin, Texas, United States, 2 Physics, Arizona State University, Tempe, Arizona, United States, 3 Materials Science and Engineering, University of Texas at Dallas, Richardson, Texas, United States
Show AbstractPerovskite oxides exhibit a wide variety of properties including superconductivity, colossal magnetoresistance, ferroelectricity, and ferromagnetism, making them excellent materials for many types of electronic devices and sensors. Because of the close interplay between the lattice and electronic degrees of freedom in the perovskites, large changes in the functional behavior of these materials can be induced through epitaxial strain. To fully exploit the functionalities of the perovksite oxides in device applications, epitaxial integration with silicon is essential. One such material that is strain-sensitive is LaCoO3, a correlated oxide that normally has a diamagnetic ground state in bulk. Recently, LaCoO3 films grown by pulsed laser deposition on single crystal SrTiO3 have been shown to exhibit ferromagnetic order as a result of tensile strain. Subsequent first-principles calculations of strained LaCoO3 are not in agreement about the details of how the ferromagnetism arises in this material. In this talk, we describe the development of strain-induced ferromagnetism in epitaxial layers of normally non-magnetic LaCoO3 grown on Si (100) using molecular beam epitaxy (MBE) via an epitaxial SrTiO3 buffer. Transmission electron microscopy and x-ray diffraction shows that MBE-grown LaCoO3 on SrTiO3/Si is epitaxial and tensile-strained. X-ray photoelectron spectroscopy measurements on the LaCoO3 on Si are consistent with stoichiometric LaCoO3. We also confirm that the strained LaCoO3 becomes ferromagnetic with a Curie temperature of ~85 K. In order to shed light on the origin of ferromagnetism, we also performed first-principles calculations of LaCoO3 as a function of epitaxial strain. The calculations were performed using a large simulation cell consisting of four formula units, allowing for more degrees of freedom for lattice relaxation compared to earlier calculations. The calculations show that a sufficiently large tensile strain does induce ferromagnetism. Analysis of the atomic structure shows that the ferromagnetic order is accompanied by a partial “untilting” of the CoO6 octahedra. This work is also the first demonstration of the growth of LaCoO3 using MBE, providing another avenue for the epitaxial integration of magnetism with silicon.
5:00 PM - WW13.8
First-principles Study of Strain-induced Ferromagnetism in LaCoO3.
Hosung Seo 1 , Alexander Demkov 1
1 Physics, The University of Texas at Austin, Austin, Texas, United States
Show AbstractWe study theoretically the effect of biaxial in-plane strain on magnetic properties of LaCoO3 using density functional theory within the local spin density approximation combined with the Hubbard U method (LSDA+U). LaCoO3 (LCO) is normally a non-magnetic insulator with trivalent cobalt ions in low-spin state (t2g6). Owing to close interplay between orbital, spin, and lattice degrees of freedom, it shows rich magnetic behavior such as temperature-induced spin state transition. The origin of the spin transition in the bulk is subject to some controversy [3-5]. Recently, the tensile-strained LCO film is experimentally confirmed to have ferromagnetic ground state. [1,2] The underlying mechanism to stabilize the ferromagnetic ground state is, however, unclear [6,7]. Using a large tetragonal cell with four independent LCO formula units, we calculate full structural response of the system to applied strain for both non-magnetic and magnetic solutions. We show that beyond tensile strain of 3.8% the ferromagnetic solution with Co ions in intermediate-spin state (t2g5 eg1) is stabilized accompanied by partial untilting of CoO6 octahedral network. Other significant structural features such as variation in Co-O-Co bond angle and their physical implication will be discussed. We also perform the calculation for compressive-strained structures and the difference between these and the tensile strained structures will be presented.References[1] D. Fuchs, C. Pinta, T. Schwarz, P. Schweiss, P. Nagel, S. Schuppler, R. Schneider, M. Merz, G. Roth, and H. v. Löhneysen, “Ferromagnetic order in epitaxially strained LaCoO3 thin films”, Phys. Rev. B 75, 144402 (2007).[2] A. Posadas, M. Berg, H. Seo, A. de Lozanne, A.A. Demkov, D.J. Smith, A.P. Kirk, D. Zhernokletov, and R.M. Wallace,” Strain-induced ferromagnetism in correlated oxide LaCoO3 epitaxially grown on Si (100)”, submitted to the Appl. Phys. Lett.[3] M.A. Korotin, S.Yu. Ezhov, I.V. Solovyev, and V.I. Anisimov, “Intermediate-spin state and properties of LaCoO3”, Phys. Rev. B 54, 5309 (1996).[4] K. Knizek, P. Novak and Z. Jirak, “Spin state of LaCoO3: Dependence on CoO6 octahedra geometry”, Phys. Rev. B 71, 054420 (2005).[5] H. Hsu, K. Umemoto, M. Cococcioni, and R. Wentzcovitch, “First-principles study for low-spin LaCoO3 with a structurally consistent Hubbard U”, Phys. Rev. B 79, 125124 (2009).[6] J.M. Rondinelli and N.A. Spaldin, “Structural effects on the spin-state transition in epitaxially starined LaCoO3 films”, Phys. Rev. B 79, 054409 (2009).[7] K. Gupta and P. Mahadevan, “Strain-driven magnetism in LaCoO3 thin films”, Phys. Rev. B 79, 020406 (2009).
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Defect Related Magnetism in LaCoO3 Epitaxial Films.
Virat Mehta 1 2 , Yuri Suzuki 1 2
1 Materials Science and Engineering, UC Berkeley, Berkeley, California, United States, 2 Material Sciences Division, Lawrence Berkeley National Laboratories, Berkeley, California, United States
Show AbstractBulk LaCoO3(LCO) exhibits a complex spin behavior involving a transition from a low-temperature diamagnetic state to a high-temperature paramagnetic state; however, recent studies of epitaxial thin films of LCO surprisingly show ferromagnetism (FM) up to 80K [1, 2]. The insulating FM behavior has been attributed to tetragonal distortions due to epitaxial mismatch with the substrate [2, 3, 4] or slight oxygen or cation non-stoichiometry [5]. The source of the long-range ordering is still not very well understood. In this work we report on the anomalous magnetic properties observed in films grown on (001)-oriented LaAlO3 (LAO) and SrTiO3 (STO) substrates as a function of the growth conditions and degree of epitaxy to the substrate. X-ray diffraction shows that our films grown on STO substrates are under in-plane biaxial tension while those grown on LAO are under biaxial compression. In either case, the films exhibit tetragonal unit cells at lower thicknesses. With increasing thickness, the lattice parameters relax towards the psuedocubic bulk value for LCO of ~3.81 Å. SQUID magnetometry shows the Curie temperature of ~80K does not vary significantly for different films and film thicknesses. Omega rocking curve scans at the 002 peak show increasing FWHM with increasing thickness indicating an increase in mosaicity of the films. The increasing relaxation and mosaic spread in the films with increasing thickness may be associated with a possible increase of defects in the film. The coherently strained thin films show a saturated moment ~0.8μB/Co on STO, and ~0.4μB/Co on LAO with the field applied in the in-plane direction. For films grown on LAO, the remnant magnetization (Mr) and the coercive field (Hc) increase with little change to the saturation magnetization (Ms) as the structure relaxes to the bulk. However, films on STO show a gradual decrease of Ms with increasing thickness with little change in Mr and Hc. These trends in magnetic properties as a function of increasing thickness suggest that defects may play an important role in explaining the FM in these films. Additionally, we also observe a large anisotropy in Ms for films measured with the field in-plane versus out-of-plane for all films on STO and thick films on LAO. Coherently strained films, less than 50 nm thick, on LAO do not show this anisotropy. This anisotropy cannot be explained by background errors or impurities in the substrate but may help shed light on the origin of FM in epitaxial LCO thin films.[1] D. Fuchs, C. Pinta, T. Schwarz, P. Schweiss, P. Nagel, S. Schuppler, R. Schneider, M. Merz, G. Roth, and H. v. Loehneysen, Phys. Rev. B 75 144402 (2007). [2] D. Fuchs, E. Arac, C. Pinta, S. Schuppler, R. Schneider, and H. v. Loehneysen. Phys. Rev. B 77 014434 (2008). [3] J. Rondinelli and N. Spaldin, Phys. Rev. B 79 054409 (2009).[4] K. Gupta and P. Mahadevan Phys. Rev. B 79 020406 (2009).[5] J. Freeland, J. Ma, and J. Shi, Appl. Phys. Lett. 93 212501 (2008).