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2011 MRS Spring Meeting & Exhibit

April 25-29, 2011 | San Francisco
Meeting Chairs: Ping Chen, Chang Beom-Eom, Samuel S. Mao, Ryan O'Hayre

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Symposium WW : Multiferroic, Ferroelectric, and Functional Materials, Interfaces, and Heterostructures

2011-04-25 Show All Abstracts

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

WW1: Materials Composition and Defects

Session Chairs

Thomas Tybell

Monday PM, April 25, 2011

Room 2018 (Moscone West)

10:00 AM - **WW1.1

Defects in Ferroelectric Oxide-based Materials.

Clive Randall ¹, Russell Maier ¹, Soonil Lee ¹
¹Materials Science & Engineering, Pennsylvania State University, University Park, Pennsylvania, United States

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10:30 AM - **WW1.2

Synthesis, Stability and Composition Control of Multiferroic and Ferroelectric Perovskite Materials.

Tor Grande ¹
¹Materials Science and Engineering, NTNU, Trondheim Norway

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11:00 AM - WW1

BREAK

11:30 AM - WW1.3

Incommensurabilities and Hidden Degrees of Freedom in Multiferroics.

Dennis Meier ^{1 2}, Naemi Leo ², Ladislav Bohaty ³, Petra Becker ³, Ramamoorthy Ramesh ¹, Manfred Fiebig ²
¹Materials Science and Engineering, UC Berkeley, Berkeley, California, United States, ²HISKP, University Bonn, Bonn, NRW, Germany, ³Institute of Crystallography, University of Cologne, Cologne, NRW, Germany

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11:45 AM - WW1.4

Stoichiometry Dependence of Defect Complexes on the Cu²⁺ Doped Alkali Niobate Piezoceramics Monitored by Electron Paramagnetic Resonance.

Ebru Erunal ¹, Rudiger Eichel ¹, Jerome Acker ², Hans Kungl ², Micheal Hoffmann ²
¹Ins. f. Phys. Chem., University of Freiburg, Freiburg i.Br. Germany, ²Ins. f. Ceramics in Mech. Eng., Karlsruhe Institute of Technology, Karlsruhe Germany

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12:00 PM - WW1.5

Extrinsic and Intrinsic Defect Interplay in Lanthanum Doped Strontium Titanate.

Elif Ertekin ¹, Varadharajan Srinivasan ², Jeffrey Grossman ¹
¹, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, ², Indian Institute of Science Education and Research, Bhopal India

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Due to its diverse and remarkable properties, Strontium Titanate (SrTiO3) has been the focus of renewed research efforts and interest in recent years. Some of these properties include an electron--doping induced insulator to metal transition, low temperature superconductivity, the formation of two--dimensional electron gases at the interface of SrTiO3 and polar oxides, blue light emission, and defect induced ferroelectricity. The Oxygen vacancy, understood to be an electron donor in SrTiO3, is currently considered to lie at the heart of most (if not all) of these properties. However, experimental evidence of other intrinsic defects such as Strontium vacancies and their complexes have also been reported in the literature. Also, recent Hall effect measurements indicate that the metal insulator transition in Lanthanum (La) doped SrTiO3 epitaxial thin films is reduced unless low oxygen partial pressures are present during growth, indicating the possible influence of other intrinsic defects that reduce carrier concentrations.Although identifying the source of the observed properties depends on understanding the combined interplay between intrinsic defects such as vacancies (as well as extrinsic doping agents), this complex point defect phase space has not yet been fully and systematically explored. Using total energy electronic structure methods based on density functional theory, we explore the formation energies of neutral and charged point defects in intrinsic and extrinsically doped SrTiO3. Based on our results, we construct a point defect phase diagram for n-type, p-type, or intrinsically pure SrTiO3. In the case of Lanthanum doped SrTiO3, Lanthanum as a substitutional impurity for Strontium is understood to be an electron donor in SrTiO3. Our calculations suggest that native compensating point defects present at high Lanthanum doping concentrations may be responsible for the observed reduction of the carrier concentration in Hall effect measurements. These findings also suggest that compensating point defects may be involved in the formation of transparent conducting oxides from Lanthanum doped SrTiO3.

12:15 PM - WW1.6

(Anti)Ferroelectric Ultra-thin Epitaxial PbZrO3 Films.

Ayan Roy Chaudhuri ¹, Miryam Arredondo ¹, Alessio Morelli ¹, Ionela Vrejoiu ¹
¹, Max Planck Institute of Microstructure Physics, Halle (Saale) Germany

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Antiferroelectric materials (AFE’s), unlike ferroelectrics (FE’s), undergo a structural phase transition from a high temperature paraelectric (PE) non-polar state to an anti-polar state with decrease in temperature. Under sufficiently large applied electric field these materials can undergo an electric field driven transition to a FE phase which again switches back to the AFE state on removal of the electric field. Therefore AFE’s are characterized by a double polarization hysteresis (P-E) loop and zero remnant polarization (Pr). PbZrO3 (PZO) is a well known AFE oxide possessing perovskite structure. At room temperature PZO possesses an orthorhombic unit cell which under an applied electric field transforms to a rhombohedral FE phase. Previous investigations suggested that the FE phase of PZO can be stabilized in thin films. Ferroelectricity was observed in polycrystalline thin films of PZO on Si with reducing PZO layer thickness and has been explained in terms of the effect of the built in electric field at the PZO/Si interface. In epitaxial PZO thin films the P-E responses were found to be dependent on the orientation of the film. Depending on the film orientations FE switching and co-existing FE and AFE switching have been reported for epitaxial PZO thin films. Further, rhombohedral FE phase was observed in PZO/Pb(Zr0.8Ti0.2)O3 heterostructures below a critical layer thickness. All these observations suggested that elastic strain might possibly play a significant role in stabilizing the FE phase in PZO thin films under a critical thickness.In order to investigate the role of substrate induced lattice strain on epitaxial PZO thin films and to establish the structure-property correlation we have selected three different single crystal substrates [SrTiO3 (100), DyScO3 (110) and GdScO3(110)] to vary the substrate induced elastic strains on PZO. Epitaxial PZO(120) thin films of thicknesses ranging between 3-40 nm were deposited by pulsed laser ablation on the substrates coated with a thin SrRuO3 (SRO) layer. All the samples exhibited pure PZO phase with smooth surface. X-Ray Diffraction measurements in the θ-2θ geometry and reciprocal space mapping indicated a possible distortion in the crystal structure of the PZO ultra-thin films (<10 nm) under epitaxial strain. Detailed structural characterizations were performed by HRTEM measurements. Room temperature P-E measurements exhibited a mixed FE and AFE behaviour for the PZO films and an increase in Pr was observed with reducing the PZO layer thickness. Piezoresponse Force Microscopy measurements and a large Pr (~ 20 μC/cm2) observed for PZO films of ~ 30 nm thickness indicated the existence of ferroelectricity in PZO films. The structural distortion accompanied by the increase in Pr values with reducing PZO layer thickness suggested elastic strain mediated stabilization of FE phase in ultra-thin epitaxial PZO films.

12:30 PM - WW1.7

Light-induced Control of the Polarization in PbTiO3 Ferroelectric Nanolayers.

Dan Daranciang ¹, Matthew Highland ², Harold Hwang ³, Nathaniel Brandt ³, Haidan Wen ², Klaus Sokolowski-Tinten ⁶, Jorgen Larsson ⁴, David Reis ⁵, Keith Nelson ³, Paul Fuoss ², G. Stephenson ², Aaron Lindenberg ^{1 5}
¹Materials Science, Stanford University, Stanford, California, United States, ²Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States, ³Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, ⁶, University of Duisberg-Essen, Duisberg Germany, ⁴Physics, Lund Institute of Technology, Lund Sweden, ⁵Photon Science, SLAC National Accelerator Laboratory, Menlo Park, California, United States

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12:45 PM - WW1.8

Structural and Magnetic Properties of Cobal Ferrite – Barium Titanate Nanotube Arrays.

Dario Bueno-Baques ¹, Veronica Corral-Flores ¹, Norma Morales-Carrillo ², Alejandro Torres-Castro ³, Hector Camacho-Montes ⁴, Ronald Ziolo ¹
¹Advanced Materials, Centro de Investigacion en Quimica Aplicada, Saltillo, Coahuila, Mexico, ², Instituto Tecnologico de Saltillo, Saltillo, Coahuila, Mexico, ³FIME, Universidad Autonoma de Nuevo Leon, Monterrey, Nuevo Leon, Mexico, ⁴Institute for Engineering and Technology , Universidad Autónoma de Ciudad Juarez, Ciudad juarez, Chihuahua, Mexico

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WW2: Ferroelectric Domains

Session Chairs

Tor Grande

Monday PM, April 25, 2011

Room 2018 (Moscone West)

2:30 PM - **WW2.1

Nanoscale-engineered Tunable Microwave Dielectrics.

Che-Hui Lee ^{1 2}, Turan Birol ³, Nathan Orloff ^{4 5}, Ye Zhu ³, Lena Kourkoutis ³, Veronica Goian ⁶, Ryan Haislmaier ², Eftihia Vlahos ², Michael Biegalski ⁷, Nicole Benedek ³, Margitta Bernhagen ⁸, Yongsam Kim ³, Joel Brock ³, Reinhard Uecker ⁸, Venkatraman Gopalan ², Stanislav Kamba ⁶, Xiaoxing Xi ⁹, David Muller ^{3 10}, Ichiro Takeuchi ¹¹, James Booth ⁴, Darrell Schlom ¹, Craig Fennie ³
¹Materials Science and Engineering, Cornell University, Ithaca, New York, United States, ²Department of Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania, United States, ³School of Applied and Engineering Physics, Cornell University, Ithaca, New York, United States, ⁴, National Institute of Standards and Technology, Boulder, Colorado, United States, ⁵Department of Physics, University of Maryland, College Park, Maryland, United States, ⁶, Institute of Physics ASCR, Prague Czech Republic, ⁷Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, ⁸, Leibniz Institute for Crystal Growth, Berlin Germany, ⁹Department of Physics, Temple University, Philadelphia, Pennsylvania, United States, ¹⁰, Kavli Institute at Cornell for Nanoscale Science, Ithaca, New York, United States, ¹¹Department of Materials Science and Engineering, University of Maryland, College Park, Maryland, United States

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3:00 PM - **WW2.2

Probing Local Ionic Motion and Conductivity Phenomena in Correlated Oxides.

Sergei Kalinin ^{1 2}, Stephen Jesse ¹, Amit Kumar ¹, Arthur Baddorf ¹, Peter Maksymovych ¹, Nina Balke ¹, Michael Biegalski ¹, Donovan Leonard ², Albina Borisevich ²
¹The Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, ²Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States

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3:30 PM - **WW2.3

Real-time Studies of Ferroelectric Switching and Spontaneous Vortex Nanodomain Arrays at Ferroelectric Heterointerfaces.

Xiaoqing Pan ¹, Christopher Nelson ¹, Yi Zhang ¹, Peng Gao ¹, Benjamin Winchester ², Yijia Gu ², Colin Heikes ³, Alexander Melville ³, Carolina Adamo ³, Chad Folkman ⁴, Seung-Hyub Baek ⁴, Chang-Beom Eom ⁴, Darrell Schlom ³, Long-Qing Chen ²
¹Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States, ²Materials Science and Engineering, Penn State University, University Park, Pennsylvania, United States, ³Materials Science and Engineering, Cornell University, Ithaca, New York, United States, ⁴Materials Science and Engineering, University of Wisconsin , Madison, Wisconsin, United States

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Polarization switching between energetically equivalent states in ferroelectric materials, such as in ferroelectric memory, is a complex and inhomogenous process dominated by interfaces and defects. These interfaces and defects influence the configuration of domain walls, their stability and mobility. Real-time microscopic observation of ferroelectric switching process is critical to understanding the switching mechanisms of ferroelectric domains and developing nanosacle ferroelectric devices such as non-volatile memories. Here we present direct observations of ferroelectric switching in a single crystal BiFeO3 thin film using in situ transmission electron microscopy (TEM) with a custom-designed scanning tunneling microscopy holder. We find that the switching of ferroelectric domains in BiFeO3 is thermodynamically limited by ferroelastic strain energy during the growth of newly nucleated domains, in contrast to the typical process that is kinetically limited by the nucleation of domains. Several video clips will be shown to demonstrate the real-time studies of nucleation, growth, defect pinning, and stability of ferroelectric domains under an applied electric field. We will also present atomic resolution images of the polarization of the ferroelectric BiFeO3 subjected to different electrical boundary conditions using a spherical aberration-corrected TEM. Unusual triangular-shaped spontaneous vortex nanodomains are seen and their role in providing polarization closure is understood through phase-field simulations. This first observation of vortex nanodomain arrays at ferroelectric hetero-interfaces reveals properties unlike the surrounding film including mixed Ising-Néel domain walls, which will affect switching behavior, and a drastic increase of in-plane polarization. The importance of magnetization closure has long been appreciated in multidomain ferromagnetic systems; imaging this analogous effect with atomic resolution at ferroelectric hetero-interfaces provides the ability to see device-relevant interface issues.

4:00 PM - WW2

BREAK

4:30 PM - WW2.4

Domain Bundle Boundaries in Single Crystal BaTiO3 Lamellae: Searching for Naturally Forming Dipole Flux-closure / Quadrupole Chains.

Leo McGilly ¹, Alina Schilling ¹, John Gregg ¹
¹Centre for Nanostructured Media, Queen's University Belfast, Belfast, Northern Ireland, United Kingdom

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4:45 PM - WW2.5

Cross-sectional Imaging of 90° `Bundle’ Mediated Domain Switching in Free-standing Single Crystal BaTiO₃ Thin Film Capacitors by Piezoresponse Force Microscopy.

Raymond McQuaid ¹, Leo McGilly ¹, Pankaj Sharma ², Alexei Gruverman ², Marty Gregg ¹
¹Physics and Astronomy, Queen's University Belfast, Belfast, Antrim, United Kingdom, ²Physics and Astronomy, University of Nebraska, Licoln, Nebraska, United States

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In recent years, PFM has emerged as a formidable technique for characterising capacitor switching by permitting nanoscale imaging of domain configurations at different stages of polarisation reversal. However in PFM studies emulating switching in typical capacitor stack geometries (top electrode - ferroelectric thin film – bottom electrode), where the SPM probe images polarisation orientation through the top electrode, complications interpreting the thickness averaged piezoresponse precludes explicit tracking of domain growth through the film thickness. In order to circumvent this limitation and visualise domain propagation between the electrodes, a co-planar arrangement can be employed – in essence PFM of the capacitor cross section (e.g. APL 89, 082906 (2006), Adv. Func. Mater. 20, 3466, (2010)).

Combining this technique with an established Focused Ion Beam (FIB) based methodology for fabricating single crystal BaTiO₃ thin films we investigate domain switching in 300nm thick films freely suspended across an interelectrode gap (FIB milled between co-planar platinum electrodes). The film is oriented with [100] direction aligned with the homogenous planar applied field such that textbook 180° domain switching, by growth of either of two anti-aligned in-plane domain variants, is anticipated. Instead, a global ‘ac’ domain structure is consistently observed with ‘ac’ stripes oriented parallel to the electrodes. This configuration persists even for fully switched structures, where a monodomain state would traditionally be expected, with ‘a’ domains aligned with the field and ‘c’ domains out-of-plane. Intermediate switched states are accommodated by 90° domain ‘bundles’ with associated bundle boundaries (typically extending fully between electrodes) across which the in-plane polarisation component of the ‘ac’ stripes is seen to reverse orientation (by 180°). In particular cases, the out-of-plane polarisation component is observed to maintain the same orientation across this boundary, seemingly producing an (electrostatically) energetically unfavourable 90° domain configuration on one side of the boundary with head-head (or tail-tail) oriented dipoles across the ‘ac’ stripe domain walls. Most interestingly, PFM imaging with in-situ switching field application shows that switching is in fact mediated by motion of these ‘bundle’ type boundaries - reversing regions with opposing ‘a’ domain orientation towards field alignment.

5:00 PM - WW2.6

In-situ TEM Studies of Ferroelectric Switching in Multiferroic BiFeO₃ Thin Films.

Christopher Nelson ¹, Peng Gao ¹, Pingping Wu ², Yijia Gu ², Benjamin Winchester ², Colin Heikes ³, Alexander Melville ³, Carolina Adamo ³, Chad Folkman ⁴, Seung-Hyub Baek ⁴, Chang-Beom Eom ⁴, Darrell Schlom ³, Long-Qing Chen ², Xiaoqing Pan ¹
¹Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States, ²Materials Science and Engineering, Penn State University, University Park, Pennsylvania, United States, ³Materials Science and Engineering, Cornell University, Ithaca, New York, United States, ⁴Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States

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The switching between ferroelectric polarization states under an applied electric field is integral to many applications such as non-volatile memories. This process is known to be dominated by the nucleation and growth of new domains described by three steps: domain nucleation, rapid forward growth parallel to the electric field, and slow lateral growth. The reaction kinetics are dominated by inhomogeneities such as charged defects, dislocations, and interfaces. In this work we study the switching of multiferroic BiFeO₃ thin films in-situ using a positionable scanning probe integrated with a transmission electron microscopy (TEM) holder. This enables a real-time observation of the ferroelectric switching at the nanoscale.We first studied a single domain (001) BiFeO₃ film of 800 nm in thickness grown on a miscut SrTiO₃ substrate with a SrRuO₃ electrode buffer layer. We found that a 180° reversed domains nucleates at the local high electric field at the film surface directly beneath the tip and predominately propagates downward, resulting in a thin slice of a reversely poled region separated by inclined domain walls. Secondly, we switched a 100 nm thick BiFeO3 film grown on (110) TbScO₃ with a La_0.7Sr_0.3MnO₃ bottom electrode. We found that the switching path is voltage dependant. At low fields only the out-of-plane component is reversed producing ferroelastic 71° switching. Unexpectedly, new domains nucleate at the interface with the bottom electrode and switching initially proceeds across the entire interface in the near-tip region before the domain propagates to the surface. This suggests a low nucleation barrier at the interface. The result is the formation of a single domain separated by vertical 71° domain walls which corresponds well with our phase-field simulations. At higher electric fields the in-plane components are also reversed resulting in either multidomain or 180° switching. We also show the domain wall pinning by defects and by preexisting domain walls.

5:15 PM - WW2.7

Strain Effect on Ferroelectric Switching Dynamics of Epitaxial PbZr_0.52Ti_0.48O₃ Films.

Andreas Herklotz ¹, Kathrin Dorr ¹, Michael Biegalski ², Hans Christen ²
¹, IFW Dresden, Dresden Germany, ²CNMS, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States

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Elastic strain is known to change ferroelectric properties of thin films, and its effect on the spontaneous and the remanent polarization is well studied. Less understood and little measured is the influence of the lattice strain on the ferroelectric switching dynamics. In this work, reversible biaxial strain has been applied to films grown epitaxially on piezoelectric substrates for a study of their strain-dependent ferroelectric switching. Ferroelectric PbZr_0.52Ti_0.48O₃ (PZT) films have been grown by pulsed laser deposition on piezoelectric substrates of 0.72PbMg_1/3Nb_2/3O₃-0.28PbTiO₃(001) (PMN-PT) buffered with a SrRuO₃/SrTiO₃ double layer. Four-circle x-ray diffraction has been employed to confirm the tetragonal symmetry and to measure the lattice parameters (a, c) of the films. The change of a and c upon the electrically (reversibly) controlled piezoelectric compression of the substrate (of 0.1 – 0.15 %) and the resulting Poisson number have been determined. Temperature-dependent measurements indicate the absence of a structural transition (as it would be present in the bulk phase) in the films between 300 K and 90 K. Ferroelectric polarization loops recorded in reversibly controlled strain states and at varied temperatures using a capacitor-like contact geometry reveal an enhancement of both, the remanent polarization (P_r) and the coercive field under compression. The strain dependence of P_r can thus be compared to predictions from simulations. Measurements of the switching current resulting from the application of short voltage pulses serve to determine characteristic switching times at controlled temperatures and strain states. Clearly, the switching time (t_sw) of the PZT films is responsive to the applied reversible strain. An increase of t_sw by a few percent is observed upon biaxial compression of the films. Hence, the ferroelectric switching dynamics are found to be similarly sensitive to strain as the remanent polarization. However, the underlying physical mechanisms are not yet known. We attempt to disentangle the contributions from the strain dependences of the nucleation rate and the wall velocity of ferroelectric domains.

5:30 PM - WW2.8

Direct Imaging of the Domain Switching Behavior in the Ferroelectric Polymer Films.

Pankaj Sharma ¹, Timothy Reece ¹, Shashi Poddar ¹, Stephen Ducharme ¹, Alexei Gruverman ¹
¹Department of Physics and Astronomy, University of Nebraska, Lincoln, Nebraska, United States

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2011-04-26 Show All Abstracts

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

WW3: Interface Engineering

Session Chairs

Evgeny Tsymbal

Tuesday AM, April 26, 2011

Room 2018 (Moscone West)

9:30 AM - **WW3.1

Polar Semiconductors from Metallic Perovskites: A First Principles Investigation.

Karin Rabe ¹, Jun Hee Lee ¹, Joseph Bennett ¹
¹Physics and Astronomy, Rutgers University, Piscataway, New Jersey, United States

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10:00 AM - **WW3.2

Interface Engineering in Manganites: From Diodes to Transistors.

Harold Hwang ¹
¹Applied Physics & Photon Science, Stanford University, Stanford , California, United States

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10:30 AM - WW3.3

Tuning Ferromagnetism in Perovskite Oxide Superlattices through Interfacial Effects.

Fan Yang ¹, Gu Meng ¹, Nihan Kemik ¹, Elke Arenholz ², Mike Biegalski ³, Hans Christen ³, Yayoi Takamura ¹
¹Department of Chemical Engineering and Materials Science, University of California, Davis, Davis, California, United States, ²Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California, United States, ³Center for Nanophase Materials Science, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States

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Perovskite oxides possess intriguing and technologically important physical properties such as ferromagnetism, superconductivity, and ferroelectricity. In particular, interfacial effects in superlattice structures resulting from structural distortions as well as band and charge discontinuities can introduce enhanced or completely unexpected properties compared to the individual constituent materials. Recently, we have shown that in superlattices consisting of the antiferromagnetic (AFM) insulator La0.7Sr0.3FeO3 (LSFO) and the ferromagnetic (FM) metal La0.7Sr0.3MnO3 (LSMO), a delicate balance exists between different magnetic interactions (exchange coupling, electronic reconstruction, and long-range interactions) at these interfaces.1 In this system, the charge transfer that occurs from Mn to Fe at the interfaces, leads to the accelerated degradation of the FM properties of the LSMO sublayers with decreasing sublayer thickness, while the AFM properties of the LSFO sublayers are weakly dependent on sublayer thickness. In order to further characterize the charge transfer effect, we have grown superlattices composed of LSMO and the non-magnetic metal, La0.5Sr0.5TiO3 (LSTO) with similar sublayer thickness. Due to the nature of the charge transfer effect, the LSMO sublayers in the LSMO/LSTO system display much higher Curie temperature, TC and saturation magnetization, MS, than the LSMO sublayers with equivalent thickness in the LSMO/LSFO system. Furthermore, by growing the LSMO/LSTO superlattices on different single crystal oxide substrates, we demonstrate that increasing tetragonal distortions decrease the TC and MS of the LSMO layers, increase the coercive field, and change the temperature dependence of the resistivity and magnetoresistance. The combined effects of charge transfer and epitaxial strain provide a versatile method to tune the FM properties of the LSMO sublayers for specific applications. The research at the ALS and the CNMS is funded by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy, and the work at U.C. Davis by the National Science Foundation Award DMR-0747896.[1] Y. Takamura, F. Yang, N. Kemik, E. Arenholz, M. D. Biegalski, and H. M. Christen, Phys. Rev. B 80, 180417(R) (2009).

10:45 AM - WW3.4

Control of the Octahedral Tilts in Lanthanum Cobaltite and the Impact on Magnetic Properties.

Michael Biegalski ¹, Haile Ambaye ², Valeria Lauter ², Hans Christen ¹
¹Center for nanophase materials science, Oak Ridge National Lab, Oak Ridge, Tennessee, United States, ²Neutron Scattering Science Division, Oak Ridge Nationl Lab, Oak Ridge, Tennessee, United States

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Strain effects in ABO₃ perovskite thin films have been an area of great interest for optimizing the properties of materials. Strain can be accommodated in two ways in perovskite materials, either via the extension of bond lengths or the rotation of the relatively rigid BO₆ octahedra. The strain effect via bond length changes has been well studied in ferroelectric materials. However, the effects of octahedral rotations on the magnetic properties have not been well explored. In this experiment we aim to determine the effects of these octahedral tilts on the magnetization in LaCoO₃ thin films where theory has predicted that there is a distinct difference between the effects of bond lengthening and octahedral tilting on magnetization. To explore the effects of octahedral tilts, we have used epitaxy to control the octahedral tilting in the unit cell of La_0.5Sr_0.5CoO₃ by growth on orthorhombic and cubic perovskite substrates, where orthorhombicity originates from octahedral tilts in the substrate. A cubic substrate can reduce the octahedral tilting in the unit cell by templating the cubic structure into the film, whereas an orthorhombic substrate can induce an octahedral tilt different from that in bulk La_0.5Sr_0.5CoO₃ material. Two substrates with different octahedral tisl but nearly identical mactroscopic latticer parameter of a = 3.87 Å were chosen: La_0.3Sr_0.7Al_0.65Ta_0.35O₃ (LSAT) and NdGaO₃. NdGaO₃ has the orthorhombic GdFeO₃ structure, while, LSAT has the Pm3m cubic structure. From X-ray diffraction, the films grown on LSAT were shown to have a cubic structure whereas the films grown on NdGaO₃ show an orthorhombic distortion. However, the large paramagnetic response of the NdGaO₃ prohibited the use of vibrational magnetometry. Therefor polarized neutron reflectometery was used to probe the magnetic structure of the film. The polarized neutron reflectometry demonstrates that the magnetization shows a much smaller interaction with the polarized neutrons for the sample grown on LSAT, as compared to the film grown on NdGaO₃. This suggests that the changes in the crystal structure due to the epitaxially imposed symmetries alter the magnetism in these materials.

This research was conducted at Oak Ridge National Laboratory's Center for Nanophase Materials Sciences, and Spallation Neutron Source, which is sponsored by the Scientific User Facilities Division, U.S. Department of Energy.

11:00 AM - WW3

BREAK

11:30 AM - **WW3.5

Complex Magnetic Oxides Superlattices.

Ulrike Luders ¹, Adrian David ¹, Philippe Boullay ¹, Subhash Thota ¹, Raymond Fresard ¹, Alexandre Wahl ¹, Wilfrid Prellier ¹
¹CRISMAT/UMR6508, CNRS/ENSICAEN, Caen France

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12:00 PM - WW3.6

Electronically Sharp Ruddlesden-Popper Type Oxide Heterointerfaces.

Mikko Matvejeff ^{1 4}, Kohei Yoshimatsu ², Kazunori Nishio ¹, Ryota Takahashi ¹, Hiroshi Kumigashira ^{2 3}, Masaharu Oshima ^{2 3}, Mikk Lippmaa ¹
¹, Institute for Solid State Physics, University of Tokyo, Tokyo Japan, ⁴, Aalto University, Espoo Finland, ², Department of Applied Chemistry, University of Tokyo, Tokyo Japan, ³, CREST, Japan Science Technology Agency, Tokyo Japan

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Strong electronic coupling across interfaces in perovskite heterostructures arises from the presence of continuous metal-oxygen-metal chains that allow for efficient d-level hybridization between B-site transition metal ions on either side of the interface. This often leads to significant changes in the electronic structure of the interface layers and the formation of accumulation or depletion layers that are at least a few unit cells thick and thus poses significant challenges for fabricating heterostructure-based devices, such as quantum wells, that depend on the presence of electronically sharp interfaces. We show that the fabrication of a non-perovskite interface between two perovskite oxides can prevent the formation of unwanted depletion or accumulation layers and facilitates improved control over the interface electronic structure.Ruddlesden-Popper (RP) type structure is a promising candidate for such interface buffer layer since the adjacent perovskite-type sub-units of the RP structure are separated in the c-axis direction by an electrically insulating (AO)₂ rock-salt layer. The rock-salt type layer breaks the continuous metal-oxygen-metal chains that electronically couple neighboring unit cells in the perovskite structure, rendering the RP interface inherently resistant against charge transfer along the c-axis direction. Integration of a RP-type interface layer between two perovskite oxides can therefore be a simple technique for fabricating planar junction-type oxide devices based on not only structurally but also electronically sharp oxide heterointerfaces.To demonstrate this, we look at the interfacial electronic structure of (La,Sr)MnO₃ (LSMO) / (La,Sr)FeO₃ (LSFO) heterostructures, incorporating either traditional perovskite or RP-type interfaces. It has previously been demonstrated that electron transfer from LSMO to LSFO leads to a significant increase in the effective hole-doping level at the LSMO interface and the destruction of the desired ferromagnetic order. In contrast, we show that the unwanted charge transfer can be prevented and the desired, bulk-like electronic structure of LSMO preserved in a LSFO/LSMO heterostructure where perovskite layers are separated by a RP-type interface layer consisting of (La,Sr)O.

12:15 PM - WW3.7

Chemically-driven Nanoscopic Magnetic Phase Separation at the SrTiO₃(001)/La_1-xSr_xCoO₃ Interface.

Maria Torija ¹, Manish Sharma ¹, Jaume Gazquez ^{2 3}, Maria Varela ^{2 3}, Chunyong He ¹, Josh Schmitt ¹, Julie Borchers ⁴, Mark Laver ⁴, Sami El-Khatib ^{1 4 5}, Chris Leighton ¹
¹Chem E and Mat Sci, University of Minnesota, Minneapolis, Minnesota, United States, ², Oak Ridge National Lab, Oak Ridge, Tennessee, United States, ³, Universidad Complutense de Madrid, Madrid Spain, ⁴, National Institute of Standards and Technology, Gaithersburg, Maryland, United States, ⁵, University of Maryland, College Park, Maryland, United States

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The remarkable functionality of complex oxides, when combined with the favorable lattice matching that is possible at their interfaces, provides many opportunities for new physics and applications. The perovskite manganites and cobaltites are excellent examples, being of interest in gas sensing, catalysis, and as electrodes in ferroelectric memory and solid oxide fuel cells. From the magnetism perspective they have potential for high conduction electron spin polarization, and a variety of functional ground states. However, the same delicate balance between phases that provides such impressive functionality also leads to a serious problem; it can be difficult to maintain desired properties (e.g. high spin polarization and conductivity) all the way to the interface with a dissimilar oxide. This is exemplified by magnetic tunnel junctions for example, where the interface spin polarization is suppressed and drops rapidly with temperature. In this work, using SrTiO3(001)/La1-xSrxCoO3 [1] as a model system, we have combined epitaxial growth by high pressure oxygen sputtering with detailed atomic-level stuctural characterization (including STEM/EELS imaging), conventional magnetometry, electronic transport, and small-angle neutron scattering (SANS). In the SrTiO3(001)/La1-xSrxCoO3 case we observe the usual degredation in magnetization and conductivity in the very thin film limit. We demonstrate that this is due to nanoscopic magnetoelectronic phase separation [2] in the interface region. Essentially, nanoscopic ferromagnetic (FM) clusters form in an insulating non-FM matrix near the interface, resulting in reduced magnetization and conductivity, even at compositions that display no such phase separation in the bulk. STEM/EELS depth profiling of the chemical composition reveals that this effect has a chemical origin, being due to subtle depth-wise variations in Sr and O content, resulting in reduced effective hole doping near the interface. Simple thermodynamic and structural arguments for the origin of these variations are provided, based on Sr dissolution energies and the critical link between strain state and O vacancy concentration provided by O vacancy ordering. Work at UMN supported by NSF and DoE (neutron scattering). Work at ORNL supported by DoE. Work at UCM supported by the European Research Council. [1] Torija, Sharma, Fitzsimmons, Varela, Wu and Leighton, J. Appl. Phys. 104 023901 (2008); Orlyanchik, Weissman, Torija, Sharma and Leighton, Phys. Rev. B. 78 094430 (2008).[2] Kuhns, Hoch, Moulton, Reyes, Wu and Leighton Phys. Rev. Lett. 91 127202 (2003); Wu, Lynn, Glinka, Burley, Zheng, Mitchell and Leighton, Phys. Rev. Lett. 94 037201 (2005).

12:30 PM - WW3.8

Control of Twinning and Periodic In-plane Structure in Epitaxial La0.7Sr0.3MnO3 Thin Films.

Jos Boschker ¹, Asmund Monsen ², Chad Folkman ³, Chang-Beom Eom ³, Erik Wahlstrom ², Thomas Tybell ¹
¹Department of Electronics and Telecommunications, NTNU, Trondheim Norway, ²Department of Physics, NTNU, Trondheim Norway, ³Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States

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12:45 PM - WW3.9

Magnetic Phase Separation-induced Coercivity Enhancement in Epitaxial SrTiO₃(001)/Nd_0.5Sr_0.5CoO₃ Films.

Manish Sharma ¹, Jaume Gazquez ^{2 3}, Maria Varela ^{2 3}, Chris Leighton ¹
¹Chem E and Mat Sci, University of Minnesota, Minneapolis, Minnesota, United States, ², Oak Ridge National Lab, Oak Ridge, Tennessee, United States, ³, Universided Complutense de Madrid, Madrid Spain

Show Abstract

The well-known deterioration in magnetic and electronic properties in the very thin limit in magnetic perovskite oxides has recently been shown to be due to interfacial magneto-electronic phase separation in a detailed study using SrTiO3(001)/La1-xSrxCoO3 as a model system [1-3]. This occurs even at doping values where no such effect exists in the bulk. Our recent work reveals that these materials also display anomalously large coercivity, an effect that is not well understood. To further investigate this phenomenon we have extended our study to Nd1-xSrxCoO3 (x = 0.5), the perovskite cobaltite with the largest known coercivity in bulk. Epitaxial Nd0.5Sr0.5CoO3 thin films were grown by high pressure reactive sputtering on SrTiO3(001), and thoroughly characterized via high resolution x-ray diffraction, x-ray reflectivity, STEM/EELS, magnetometry, and electronic transport. As in our earlier work on La1-xSrxCoO3, we observe a rapid deterioration in magnetization and conductivity below a critical thickness of about 6-7 nm. This is coincident with the onset of large intercluster-type negative magnetoresistance, confirming the existence of an interfacial magnetic phase separation effect where nanoscopic ferromagnetic clusters form in an insulating non-ferromagnetic matrix. Detailed temperature and angular-dependent magnetometry and magnetoresistance measurements reveal a strongly thickness dependent coercivity with peak values as large as 3.8 T. This should be compared to bulk values of the order of a few tens of mT. These data can be understood within a simple model where the coercivity enhancement originates from domain wall pinning in the long-range ferromagnetic overlayer due to exchange coupling to the nanoscopic ferromagnetic clusters in the interfacial phase-separated region. We demonstrate that this provides a quantitative, self-consistent description of the temperature- and thickness-dependent data, based on known cluster sizes and magnetic anisotropies. The work emphasizes the extreme sensitivity of the film magnetic properties to the existence of thin magnetically phase-separated layers at the interface. Work supported by NSF DMR and DoE (neutron scattering). [1] Torija, Sharma, Gazquez, Varela, He, Schmitt, Borchers, Laver, El-Khatib, Leighton submitted to Adv. Mater. (2010). [2] Torija, Sharma, Fitzsimmons, Varela, Wu and Leighton. J. Appl. Phys. 104, 023901 (2008).

WW4: Interface Control

Session Chairs

James Rondinelli

Tuesday PM, April 26, 2011

Room 2018 (Moscone West)

2:30 PM - **WW4.1

Control and Imaging of Boundary Magnetization in Chromia: From Room Temperature Electric Switching of Exchange Bias to Photoemission Electron Microscopy.

Christian Binek ¹, Xi Hi ¹, Yi Wang ¹, Ning Wu ¹, Aleksander Wysocki ¹, Takashi Komesu ¹, Uday Lanke ², Anthony Caruso ³, Elio Vescovo ⁴, Kirill Belashchenko ¹, Peter Dowben ¹
¹Physics & Astronomy, University of Nebraska, Lincoln, Lincoln, Nebraska, United States, ²Canadian Light Source Inc., University of Saskatchewan, Saskatoon, Saskatchewan, Canada, ³Department of Physics, University of Missouri, Kansas City , Missouri, United States, ⁴Brookhaven National Laboratory, National Synchrotron Light Source, Upton, New York, United States

Show Abstract

Voltage-controlled spintronics is of particular importance to continue progress in information technology through reduced power consumption, enhanced processing speed, integration density, and functionality in comparison with present day CMOS electronics. Almost all existing and prototypical solid-state spintronic devices rely on tailored interface magnetism, enabling spin-selective transmission or scattering of electrons. Controlling magnetism at thin-film interfaces, preferably by purely electrical means, is a key challenge to better spintronics. Currently, most attempts to electrically control magnetism focus on potentially large magnetoelectric effects of multiferroics. We report on our interest in magnetoelectric Cr₂O₃ (chromia). Robust isothermal electric control of exchange bias is achieved at room temperature in perpendicular anisotropic Cr₂O₃(0001)/CoPd exchange bias heterostructures [1]. This discovery promises significant implications for potential spintronics. From the perspective of basic science, our finding serves as macroscopic evidence for roughness-insensitive and electrically controllable equilibrium boundary magnetization in magnetoelectric antiferromagnets. The latter evolves at chromia (0001) surfaces and interfaces when chromia is in one of its two degenerate antiferromagnetic single domain states selected via magnetoelectric annealing. Theoretical insight into the boundary magnetization and its role in electrically controlled exchange bias is gained from first-principles calculations and general symmetry arguments. Measurements of spin-resolved ultraviolet photoemission, magnetometry at Cr₂O₃(0001) surfaces, and detailed investigations of the unique exchange bias properties of Cr₂O₃(0001)/CoPd including its electric controllability provide macroscopically averaged information about the boundary magnetization of chromia. Laterally resolved X-ray PEEM and temperature dependent MFM reveal detailed microscopic information of the chromia (0001) surface magnetization and provide a coherent interpretation of our results on robust isothermal electric control of exchange bias. The latter promise a new route towards purely voltage-controlled spintronics and an exciting way to electrically control magnetism.Financial support by NSF through Nebraska MRSEC, SRC/NSF Supplement to Nebraska MRSEC, CAREER DMR-0547887, NRI, and Cottrell Research Corporation.[1]Xi He, Yi Wang, Ning Wu, A. N. Caruso, E. Vescovo, K. D. Belashchenko, P. A. Dowben, and Ch. Binek, Nature Mater.9, 579–585 (2010).

3:00 PM - WW4.2

Domain Wall Dynamics and Electric Field Exchange Bias Switching.

Vassil Skumryev ^{1 2}, Vladimir Laukhin ^{1 3}, Ignasi Fina ³, Xavier Marti ³, Florencio Sanchez ³, Marin Gospodinov ⁴, Gervasi Herranz ³, Josep Fontcuberta ³
¹, Institució Catalana de Recerca i Estudis Avançats (ICREA), Barcelona Spain, ²Departament de Física, Universitat Autònoma de Barcelona, Barcelona Spain, ³, Institut de Ciència de Materials de Barcelona - CSIC, Barcelona Spain, ⁴, Institute of Solid State Physics - Bulgarian Academy of Sciences, Sofia Bulgaria

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3:15 PM - WW4.3

Electric Modulation of Magnetization in Ferroelectric-ferromagnetic Heterojunctions.

Haidong Lu ¹, Tom George ¹, John Burton ¹, Alexander Stamm ¹, Ihor Ketsman ¹, Andrei Sokolov ¹, Chung Bark ², Chang Eom ², Peter Dowben ¹, Evgeny Tsymbal ¹, Alexei Gruverman ¹
¹, University of Nebraska-Lincoln, Lincoln, Nebraska, United States, ², University of Wisconsin-Madison, Madison, Wisconsin, United States

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3:30 PM - WW4.4

Electric Field Control of the Metal-insulator Transition in Electrolyte-gated NdNiO₃ Thin Films.

Shutaro Asanuma ^{1 2}, Ping-Hua Xiang ^{1 2}, Hiroyuki Yamada ¹, Hiroshi Sato ^{1 2}, Isao Inoue ^{1 2}, Hiroshi Akoh ^{1 2}, Akihito Sawa ^{1 2}, Kazunori Ueno ³, Hidekazu Shimotani ⁴, Hongtao Yuan ⁴, Masashi Kawasaki ^{3 5}, Yoshihiro Iwasa ^{4 5}
¹Nanoelectrics Research Institute, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki, Japan, ², CREST, Tokyo, Tokyo, Japan, ³WPI-Advanced Institute for Materials Research, Tohoku University, Sendai, Miyagi, Japan, ⁴Quantum-Phase Electronics Center, School of Engineering, University of Tokyo, Tokyo, Tokyo, Japan, ⁵Correlated Electron Research Group, Riken, Wako, Saitama, Japan

Show Abstract

Metal-insulator (MI) transitions in correlated-electron materials are one of the main topics of interest in modern solid-state physics and offer a potentially novel route towards the realization of a conceptually different electronic engineering. To utilize the MI transition in electronic devices, a field effect transistor consisting of a correlated-electron material such as high-T _C cuprates and perovskite manganites for the channel, i.e., a Mott transistor, has been intensively investigated in the past decade. However, since a large number of carriers (≥ 0.1 holes or electrons per unit cell) are necessary to be doped in order to induce the MI transition in those materials, it is hard to achieve it by using conventional gate dielectrics. Therefore, for the realization of a practical Mott transistor, one requires correlated-electron materials with a MI transition attainable at significantly smaller carrier-density modulation. In this study, we use rare-earth nickelates NdNiO₃ as the channel material. NdNiO₃ displays a temperature-driven sharp MI transition due to the strong electron correlations. It is known that the transition temperature (T_MI) of NdNiO₃ can be controlled by a substitution of Ca²⁺ or Sr²⁺ for Nd³⁺, i.e., hole doping, and a mere 0.01 holes per unit cell would be sufficient to lower T_MI by 32 K. While this rate of suppression is significant, 0.01 holes per unit cell is still too high to be achieved by electrostatic methods using ordinary gate dielectrics. In response, we have employed an ionic liquid electrolyte (DEME-BF₄) as the gate dielectric. By using the electrolyte-gated transistor, we have succeeded in accumulating a large sheet carrier density >10¹⁴ holes/cm² even for small gate voltage V_G ≤ -2 V. Note that the application of a negative V_G accumulates the hole carriers at the channel. For our thinnest film (5-nm-thick NdNiO₃) and gate voltage V_G = -2.5 V, T_MI was reduced by 40 K and the resistivity just above T_MI (V_G = -2.5 V) changed by one order of magnitude. From the V_G dependence of the resistivity, the field-effect mobility μ of the 5-nm-thick NdNiO₃ thin film can be estimated to be ~440 cm²V^-1s^-1 for V_G < -2 V. Such a large μ is due to the strong nonlinear dependence of the Drude weight on doping, which is a characteristic of filling-controlled Mott transitions. This study is potentially applicable to Mott transistor devices. This work was supported in part by Funding Program for World-Leading Innovative R&D on Science and Technology (FIRST Program) of JSPS, Grant-in-Aid for Scientific Research (Nos. 21560707 and 22360280), and Grant-in-Aid for Young Scientists (No. 21750198).

3:45 PM - WW4.5

Imaging Magnetoelectric Coupling in Ferromagnetic Films on Ferroelectric Substrates.

Massimo Ghidini ^{1 2}, Xavier Moya ¹, Lee Phillips ¹, Wenjing Yan ¹, Nina Steinke ³, Rhodri Mansell ³, Chrispin Barnes ³, Francesco Maccherozzi ⁴, Sarnjeet Dhesi ⁴, Neil Mathur ¹
¹Materials Science, University of Cambridge, Cambridge United Kingdom, ², University of Parma, Parma Italy, ³Physics, University of Cambridge, Cambridge United Kingdom, ⁴, Diamond Light Source Ltd, Didcot United Kingdom

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4:00 PM - WW4

BREAK

4:30 PM - **WW4.6

Voltage-induced Magnetic Anisotropy Change in Ultrathin Fe(Co)/MgO Junctions.

Takayuki Nozaki ^{1 2}, Shinichi Murakami ¹, Yoichi Shiota ¹, Frederic Bonell ¹, Teruya Shinjo ¹, Yoshishige Suzuki ¹
¹, Osaka Univ., Toyonaka, Osaka, Japan, ², PRESTO, JST, Kawaguchi, Saitama, Japan

Show Abstract

Voltage control of magnetization switching is an ideal writing technique for future spintronic devices due to its promising feature of low-power consumption. Several kinds of experimental approaches have been made so far, for example, control of magneto-striction in a hybrid system of ferromagnetic metal layer and piezo-electric material, control of Curie temperature in ferromagnetic semiconductor, multiferroic properties, and control of magnetic anisotropy in a metallic ultrathin film [1]. We recently reported a large voltage-induced magnetic anisotropy change in an all solid state structure of epitaxial Au / ultrathin Fe(Co)/MgO/Polyimide/ITO junctions [2,3]. The large advantage of this effect is that it can be easily applied to a conventional MgO-based magnetic tunnel junction structure, which is the most important device in the field of spintronics. In this presentation, we’ll introduce our recent experimental trials, enhancement of the voltage effect by material designs and quantitative evaluation of the anisotropy energy change using electrical FMR measurements. For the first subject, we fabricated a junction structure with different buffer or ferromagnetic materials, e.g. Ag/ultrathin Fe/MgO/Polyimide/ITO and Pd/ultrathin FePd/MgO/Polyimide/ITO structures. We found clear enhancement of the perpendicular anisotropy, and also the voltage-induced anisotropy change in both cases. For example, the surface anisotropy change reaches 28 μJ/m² for the junction with the Ag buffer layer, which is more than 3 times larger than that observed in the Au / ultrathin Fe system [2]. For the second subject, we fabricated a fully epitaxial magnetic tunnel junction (MTJ) consisting of Au(50 nm) / ultrathin FeCo(0.55-0.75 nm)/MgO(1.1-2 nm)/Fe(10 nm), and investigated the voltage induced anisotropy change in tunnel magnetoresistance and electrical FMR measurements. Clear influence of the bias voltage application on the saturation field, Hs in the MR curve was observed, which implies the perpendicular magnetic anisotropy change in the ultrathin FeCo. The observed shifts in the Hs reach more than 400 Oe under the bias voltage of ±600 mV. For the accurate quantitative evaluation of the voltage-induced anisotropy energy change, we performed an electrical FMR analysis using spin-torque diode effect [4] or magnetic-noise measurements. Depending on the applied bias voltage, linear change in the FMR peak, which reflects the perpendicular magnetic anisotropy field, was observed. The slope of the electric-field induced anisotropy energy change was evaluated to be 30–40 fJ/Vm in the investigated FeCo thickness range. The electrical FMR measurement is powerful technique to evaluate the intrinsic anisotropy energy change.[1] M. Weisheit et al. Science 315, 349 (2007).[2] T. Maruyama et al. Nature Nanotechnol. 4, 158 (2009).[3] Y. Shiota et al. Appl. Phys. Express 2, 063001 (2009).[4] T. Nozaki et al. Appl. Phys. Lett. 96, 022506 (2010).

5:00 PM - WW4.7

Magnetoelectric Coupling in Composite Multiferroic Heterostructures.

Jason Hoffman ^{1 2}, Carlos Vaz ^{1 2}, Yaron Segal ^{1 2}, Matthew Marshall ^{1 2}, Fred Walker ^{1 2}, Charles Ahn ^{1 2}
¹Applied Physics, Yale University, New Haven, Connecticut, United States, ²Center for Research on Interface Structures and Phenomena, Yale University, New Haven, Connecticut, United States

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5:15 PM - WW4.8

Interface Magnetoelectric Effect in Ferroelectric/Antiperovskite Heterostructures.

Pavel Lukashev ^{1 2}, Kirill Belashchenko ¹, Evgeny Tsymbal ¹, Renat Sabirianov ²
¹Physics and Astronomy, University of Nebraska - Lincoln, Lincoln, Nebraska, United States, ²Physics, University of Nebraska at Omaha, Omaha, Nebraska, United States

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5:30 PM - WW4.9

Ferroelectrically-induced Weak Ferromagnetism in Perovskite Superlattices.

Jun Hee Lee ¹, Karin Rabe ¹
¹, Rutgers, Piscataway, New Jersey, United States

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5:45 PM - WW4.10

Polarization-controlled Two-dimensional Electron Gas at LAO/STO Interface.

Chung Wung Bark ¹, David Felker ¹, Sanghan Lee ¹, Seung Hyub Baek ¹, Chad Folkman ¹, Yong Wang ², Pankaj Sharma ², Alexei Gruverman ², Evgeny Tsymbal ², Mark Rzchowski ¹, Chang-Beom Eom ¹
¹Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States, ²Department of Physics and Astronomy and Nebraska Center for Materials and Nanoscience, University of Nebraska–Lincoln, Lincoln, Nebraska, United States

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2011-04-27 Show All Abstracts

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

WW8: Poster Session: 2DEG, Junction, Interface, Multilayers and Magnetic Oxides

Session Chairs

Wednesday PM, April 27, 2011

Salons 7-9 (Marriott)

9:00 PM - WW8.1

Magnetoelectric Properties of BST/LSMO Particulate Nanocomposites.

Juan Beltran Huarac ¹, Ricardo Martinez Valdez ¹, Omar Perez Veloz ¹, Ratnakar Palai ¹
¹Physics, University of Puerto Rico at Rio Piedras, San Juan United States

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9:00 PM - WW8.10

First Principles Study of Defective and Non-stoichiometric Sr₂FeMoO₆.

Rohan Mishra ¹, Oscar Restrepo ¹, Patrick Woodward ², Wolfgang Windl ¹
¹Materials Science and Engineering, The Ohio State University, Columbus, Ohio, United States, ²Chemistry, The Ohio State University, Columbus, Ohio, United States

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9:00 PM - WW8.11

Analysis on Interface Layer Between Pt Electrode and Ferroelectric Layer of Solution-processed PZT Capacitor.

Thanh Pham ¹, Quoc Trinh Bui ², Tue Phan ¹, Takaaki Miyasako ², Eisuke Tokumitsu ^{2 3}, Tatsuya Shimoda ^{1 2}
¹Shool of Material Science, Japan Advanced Institute of Science and Technology, Nomicity, Ishikawa, Japan, ², Japan Science and Technology Agency, ERATO, Shimoda Nano-Liquid Process Project, Nomicity, Ishikawa, Japan, ³Precision and Intelligence Laboratory, Tokyo Institute of Technology, Midori-ku, Yokohama, Japan

Show Abstract

Lead zirconate titanate (PZT) ferroelectric thin films have been of a great interest for their applications in electronic devices, such as FeRAMs, infrared sensors, etc…. The electrical properties of a metal-ferroelectric-metal capacitor using PZT material strongly depend on the properties of the contact between a metal electrode and a ferroelectric layer such as Au/PZT or Pt/PZT. It has been said that these contacts are Shottky contact and the values of the Shottky barrier heights calculated from Shottky emission generally lie in a range of 0.64 to 0.93 eV[1,2,3]. Otherwise, an interface layer (dead-layer) was believed to exist between the metal electrode and the ferroelectric layer of a metal-ferroelectric-metal capacitor. This dead-layer forms a parasitic capacitor in series with the real ferroelectric layer. Larsen et al reported that the ratios of thickness to dielectric constant in the dead-layers were estimated to be from 0.036 to 0.05 nm in the Pt/PZT/Pt capacitors[4]. Nguyen et al reported that the thickness of the dead-layer was 6.5 nm in the SRO/PZT(250 nm)/SRO capacitor[5]. However, the values of thickness and of dielectric constant of the dead-layer of solution-processed PZT capacitors with Pt electrodes have not been investigated yet.In this work, PZT films were deposited by the sol-gel technique on Pt(111)/Ti/SiO2/Si substrates. The electrical properties of the Pt/PZT/Pt capacitors were analyzed. It is found that polarization-electric field (P-E) loops and capacitor-voltage (C-V) characteristics are asymmetric, which is probably due to the existence of an interface layer (dead-layer) at the interface between the Pt electrode and the PZT film. By conducting temperature dependant measurement, the Pt/PZT/Pt capacitor was confirmed to be Shottky emission conduction, and the Sottky barrier height at Pt/PZT interface was calculated to be 0.67eV. On the basic of a series capacitors model and Shottky contact of Pt/PZT interface, the thickness and the dielectric constant of this dead-layer were estimated to be 7.1 nm and 156, respectively, through the measurements of the C-V and I-V. Moreover, the dielectric constant of 813 was obtained for the real PZT ferroelectric-layer. The existence of the dead layer between the Pt top electrode and the PZT film was also confirmed by the ellipsometer measurement, the transmission electron microscopy (TEM) observation and will be confirmed by the impedance spectroscopy method as well.[1]Y. S. Yang, et al, J. Appl. Phys. 84, 5005 (1998).[2]I. Stoilichnov, et al, J. Appl. Phys. 84, 3216 (1998).[3]J. C. Shin, et al, Appl. Phys. Lett. 75, 3411 (1999).[4]P.K. Larsen, et al, J. Appl. Phys., 76, 2045 (1994).[5]M. D. Nguyen, et al, 4th IEEE international conference on nano/micro engineered and molecular systems, vols 1 and 2, 649, (2009).

9:00 PM - WW8.12

Growth of Epitaxial Superconductor/Dielectric Heterostructures Using a Sputtering PLD Hybrid System with in-situ RHEED.

Jacob Podkaminer ¹, Chad Folkman ¹, Kwang-Hwan Cho ¹, Chang-Beom Eom ¹
¹Materials Science and Engineering, University Wisconsin-Madison, Madison, Wisconsin, United States

Show Abstract

Quantum computers, comprised of many qubits, are currently in the spotlight as the next generation of computers. Geometrically, a qubit consists of a Josephson junction or two superconducting electrodes surrounding a thin film insulator thus allowing Cooper pairs to tunnel between the superconductors in a controllable fashion. A limiting factor in superconducting qubits is decoherence caused by microscopic defects in the now standard “amorphous” tunnel layer such as nanocrystalline regions and grain boundaries¹. Growing epitaxial crystal thin films of superconducting electrodes and insulating layers could reduce the number of defects. Here we look at the epitaxial growth of superconducting Re on a sapphire substrate capped with an epitaxial oxide dielectric layer. Specifically, epitaxial Re on a c-cut sapphire substrate using DC magnetron sputtering, then transferred ex-situ to a pulsed laser deposition (PLD) system where dielectrics thin film layer is deposited.
One drawback of this fabrication approach is the necessity to expose the sample to air when the sample is transferred to different deposition chambers. The exposure irreversibly modifies the surface of the superconducting bottom electrode before deposition of the oxide dielectric barrier. In order to avoid these drawbacks, we have employed a hybrid PLD-sputtering deposition that will allow us to grow the oxide dielectric/Re heterostructures in an in-situ environment without breaking vacuum. The system is also equipped with a reflection high energy electron diffraction (RHEED) which will allow us to perform in-situ characterization of the structure and growth dynamics in different controlled environments. Using this new system we anticipate gaining new insight into the interface between a metal superconductor and dielectric layer which is important for realizing advanced superconducting devices for qubit related applications. We will discuss our strategy of epitaxial growth of various single crystal dielectrics on superconducting thin films in this system and their structural and electrical properties of the heterostructures.

¹McDermott, R. Materials Origins of Decoherence in Superconducting Qubits. Applied Superconductivity, IEEE Transactions on 19, 2-13 (2009).

9:00 PM - WW8.13

ZrO2 Layer Thickness Dependent Electrical and Dielectric Properties of BST/ZrO2/BST Multilayer Thin Films.

Santosh Sahoo ^{1 2}, D. Misra ¹, C. MacDonald ³, H. Bakhru ⁴, D. Agrawal ⁵, Y. Mohapatra ⁵
¹Electrical and Computer Engineering, New Jersey Institute of Technology, Newark, New Jersey, United States, ², National Renewable Energy Laboratory, Golden, Colorado, United States, ³Physics, University at Albany, Albany, New York, United States, ⁴College of Nanoscale Science and Engineering, University at Albany, Albany, New York, United States, ⁵Materials Science Programme, IIT Kanpur, Kanpur, UP, India

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9:00 PM - WW8.14

Thermodynamic Stability of LaAlO₃/SrTiO₃ Interface at High Temperature.

Wei Wei ¹, Alp Sehirlioglu ¹
¹Materials Science and Engineering, Case Western Reserve University, Cleveland, Ohio, United States

Show Abstract

The observation of quasi-two-dimensional electron gas (Q2-DEG) at the interface of the band insulators LaAlO₃ and SrTiO₃ has stimulated considerable research interest. However, the origin of the Q2-DEG is still under debate. Many mechanisms, both intrinsic and extrinsic, have been proposed in order to explain the formation of Q2-DEG, such as the polar catastrophe at the polar LaAlO₃/non-polar SrTiO₃ interface, structural distortions at the interface, oxygen vacancies introduced into LaAlO₃ layer during thin film growth, defects generated in the SrTiO₃ substrate due to the impingement of energetic plume species and/or substrate heating. More recently, another mechanism based on the cation intermixing at the interface has been proposed. This argument is further supported by the fact that SrTiO₃ can be doped by La and can form a conducting La_xSr_1-xTiO₃ solid solution with La content up to 40 at.%. In this abstract, the thermodynamic stability of LaAlO₃/SrTiO₃ interface has been studied by annealing the interface at elevated temperatures between 800°C and 1400°C in order to have better understanding of the interdiffusion and intermixing at the interface. The LaAlO₃/SrTiO₃ interface was developed by pulsed laser deposition. The growth temperature was 800°C and laser pulse repetition rate was 5 Hz. The interface was grown in vacuum and annealed in air at different temperatures. The depth profiles of as-deposited and annealed LaAlO₃/SrTiO₃ interfaces were carried out by X-ray photoelectron spectroscopy equipped with an argon ion sputter gun. In contrast to the La in-diffusion mechanism proposed in the literatures, the Sr out-diffusion is found to occur at relatively lower annealing temperatures. At annealing temperatures higher than 1000°C, Sr out-diffusion and La in-diffusion can occur simultaneously. X-ray Diffraction and Transmission electron microscopy were used to detailed structural characterization of the as-deposited and annealed LaAlO₃/SrTiO₃ interfaces. Electron paramagnetic resonance spectroscopy and Rutherford backscattering spectroscopy were used to study the diffusion mechanism of both the Sr and La at the interface. This project was funded by AFOSR FA 9550-09-1-0555

9:00 PM - WW8.15

Advanced Structural and Magnetic Characterization of Solution Derived Self-assembled La0.7Sr0.3MnO3 Nanoislands.

Jone Zabaleta ¹, Miriam Jaafar ², Patricia Abellan ¹, Carlos Monton ¹, Oscar Iglesias-Freire ², Carlos Ramos ³, Roberto Zysler ³, Sergio Valencia ⁴, Florian Kronast ⁴, Agustina Asenjo ², Felip Sandiumenge ¹, Narcis Mestres ¹, Teresa Puig ¹, Xavier Obradors ¹
¹, ICMAB-CSIC, Bellaterra, Barcelona, Spain, ², ICMM-CSIC, Madrid Spain, ³, Centro Atómico Bariloche and Instituto Balseiro, CNEA and Univ. Nacional de Cuyo, Bariloche Argentina, ⁴, BESSY, Helmholtz Zentrum Berlin, Berlin Germany

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9:00 PM - WW8.16

Thin Film Epitaxy and Magnetic Properties of STO/TiN Buffered ZnO on Si (001) Substrates.

Siddhartha Mal ¹, Sudhakar Nori ¹, John Prater ², Jagdish Narayan ¹
¹, North Carolina State University, Raleigh, North Carolina, United States, ², 2Materials Science Division, Army Research Office, Durham, North Carolina, United States

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9:00 PM - WW8.17

Epitaxial EuO Thin Films on GaAs.

Adrian Swartz ¹, Jared Wong ¹, Yan Li ¹, Wei Han ¹, Tao Lin ¹, Shawn Mack ², Jing Shi ¹, David Awschalom ², Roland Kawakami ¹
¹Physics and Astronomy, University of California, Riverside, RIverside, California, United States, ²Center for Spintronics and Quantum Computation, University of California, Santa Barbara, Santa Barbara, California, United States

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9:00 PM - WW8.18

Synthesis and Characterization of BaTiO3/CoFe2O4 Thin Films.

Nelcy Mohallem ¹, Helen Andrada ¹, Luciana Seara ²
¹Chemistry, Federal University of Minas Gerais, Belo Horizonte, Minas Gerais, Brazil, ²Microscopy Centre, Federal University of Minas Gerais, Belo Horizonte, Minas Gerais, Brazil

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9:00 PM - WW8.19

Influence of Near-surface and Volume Real Structure on the Electronic Properties of SrTiO₃ MIM Structures.

Juliane Seibt ¹, Florian Hanzig ¹, Hartmut Stoecker ¹, Ralph Strohmeyer ¹, Uwe Muehle ³, Cameliu Himcinschi ², Frans Munnik ⁴, Barbara Abendroth ¹, Dirk Meyer ¹
¹Institute of Experimental Physics, TU Bergakademie Freiberg, Freiberg Germany, ³Institute of Materials Science, TU Bergakademie Freiberg, Freiberg Germany, ²Institute of Theoretical Physics , TU Bergakademie Freiberg, Freiberg Germany, ⁴Institue of Ion Beam Physics and Materials Research, Research Center Dresden-Rossendorf, Dresden Germany

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Perovskite-type transition metal oxides have great potential as storage material in resistive random-access memory (RRAM) devices. Typical non-volatile memory cells are realized in metal-insulator-metal (MIM) stacks with insulator thicknesses of few nanometers.We report on the investigation of single-crystal SrTiO₃ to understand the role of volume and interface real structure for the electrical conductivity in such materials. As an alternative to Nb or Fe doped SrTiO₃, here we use a reducing annealing in high vacuum (HV) to introduce charged oxygen vacancies acting as donor centers.Structural investigations of untreated SrTiO₃ single-crystals and of the HV annealed samples were performed with X-ray diffraction, transmission electron microscopy and atomic force microscopy. Electronic properties and defect chemistry were investigated using spectroscopic methods (ellipsometry, photoluminescence and Fourier transform infrared spectroscopy). The chemical composition of the near-surface region was measured by elastic recoil detection and impurity elements were detected using atomic emission spectroscopy.The results show that initially the crystals have a highly damaged surface layer originating from cutting and polishing processes. This layer is characterized by a high density of dislocations and a stoichiometry deviating from the bulk material. In summary, vacuum annealing leads to: reduction of the surface dislocation density; introduction of point defects, namely oxygen vacancies; introduction of electrons into the conduction band and a surface reconstruction.Based on the spectroscopically determined free carrier concentration in the order of 10¹⁸ cm^-3 and considering electron mobilities reported in the literature, a resistivity of few Ωcm could be expected for our samples. Measurements using suitable electrode geometries, however, show that surface and volume resistivities are in the order of 10⁵ Ωcm and 10¹¹ Ωcm, respectively.In this context the role of the surface reconstruction layers, dislocations as conductive pathways, electronic and ionic conductivity and electronic band structure at the metal-insulator interface are discussed.

9:00 PM - WW8.2

Crystalline Orientations of Heterostructure La(Sr)MnO3 / ZnO Thin Films, and Lattice Matching Calculations.

Tamio Endo ¹, Kennichi Uehara ¹, Tatsuya Yoshii ¹, Miyoshi Yokura ¹, Tetsuo Tsuchiya ², Hiroshi Kezuka ³, Kazuhiro Endo ⁴
¹Graduate School of Engineering, Mie University, Tsu, Mie, Japan, ²Thin Film Goup, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki, Japan, ³Computer Science, Tokyo University of Technology, Hachioji, Tokyo, Japan, ⁴Integrated Technological Systems, Kanazawa Institute of Technology, Hakusan, Ishikawa, Japan

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Introduction : La(Ba)MnO3 (LBMO) and La(Sr)MnO3 (LSMO) are p-type semiconducting perovskite manganites showing versatile electrical and magnetic properties such as curious colossal magnetoresistance. ZnO is a wide-gap n-type semiconductor, which also has variety of useful properties. Recently ZnO thin film can be finely fabricated to show 2D electron gas. A goal of this study is to fabricate p-n junctions using these p-type manganites and n-type ZnO. They (LBMO/ZnO, LSMO/ZnO) are expected as new devices, because the p-n junction characteristics can be largely modulated by magnetic field, temperature and UV light. We have to, however, solve issues of variety of orientation growths prior to applications. Experimental : ZnO thin films were deposited on LAO and sapphire substrates by ion beam sputtering (IBS) at various substrate temperatures Ts and oxygen partial pressures Po using oxygen molecules or oxygen plasma. LBMO and LSMO thin films were deposited on under-layers of ZnO by the same IBS. Their crystallinities were estimated by XRD, and phase orientation ratios Ro were calculated from the peak intensities corresponding to their phases. Surface morphology and surface roughness were obtained by AFM. We calculated lattice matching in terms of lattice contraction (or expansion) of the over-layers. In this process, we considered least-common-multiples matchings and thermal lattice expansions, and obtained lattice distortion area Sd. Electrical, magnetic and optical properties on the single and double layers were characterized. Results and Discussion : Single phases of ZnO (110) and (001) were grown on LAO and sapphire, respectively. Both of ZnO (110) and (001) were grown on LSMO (001) phase. It can be explained by surface roughness of LSMO under-layers, that is, by difficulty of lattice matching. LSMO (001) single phase was grown on ZnO (110), while (001), (110) and (111) phases were grown on ZnO (001). The phase ratios Ro of (001), (110) and (111) on ZnO (001) show complicated behaviors of Po-dependences, they might be interpreted by surface energy and surface migration. LSMO (001) phase ratio is dominant at low Ts and decreases with increasing Ts. LSMO (110) phase is minimal at low Ts and increases. LSMO (111) phase is also minimal at low Ts and increases then decreases. LBMO has two phases of (110) and (111) on ZnO (001), it shows roughly the similar behaviors of Ts- dependences of the phase ratios. We tried to interpret these Ts-dependences by lattice matching calculations. Sd for LSMO (001) on ZnO (001) increases with Ts, that is the reason why Ro for LSMO (001) decreases with Ts. Thus the experimental results of Ro can be roughly interpreted by the calculated lattice matching.

9:00 PM - WW8.20

Magnetic and Magnetotransport Behaviour of Nanocrystalline Pr_1-xSr_xMnO₃ (0.40≤x≤0.60).

Anurag Gaur ¹, Neelam Maikhuri ¹, H. Singh ²
¹Department of Physics, National Institute of Technology, Kurukshetra India, ², National Physical Laboratory, New Delhi India

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Recently several experimental and theoretical studies have focused on the exploration of grain size effect on the magnetic and magnetotransport properties of alkaline earth doped rare earth perovskite manganites, chemically represented by RE_1-xAE_xMnO₃ (RE=rare earth cation and AE=alkaline earth cation) [1-3]. Since size reduction leads to increased contribution from the surface regions, the broken Mn-O-Mn bonds are indeed expected to have a definite impact on magneto-electrical properties in manganites. It has been found that in nano-manganites, size reduction below ~100 nm renders the charge and orbitally ordered (CO-OO) ground state with unstable antiferromagnetic (AFM) spin order, giving rise to a ferromagnetic (FM) ground state [2]. Moreover, the effect of material downsizing can have more dramatic effect in the vicinity of compositions that possess strong magnetic phase coexistence and hence show bicritical/multi-critical points. Among the manganites, Pr_1-xSr_xMnO₃ possesses several bi-critical/multi-critical regions on the composition-temperature (x-T) phase diagram separating paramagnetic (PM), ferromagnetic (FM), antiferromagnetic (AFM) and charge/orbital ordered (CO/OO) phases in the vicinity of x=0.5 to 0.60. Therefore, in the present work, we have tried to understand the magnetic and magneto-transport behaviour of nanocrystalline Pr_1-xSr_xMnO₃ in this critical range, x=0.40 to 0.60. The Pr_1-xSr_xMnO₃(x=0.40, 0.50, 0.55 and 0.60) nanoparticles are prepared by sol-gel based polymeric precursor route and their magnetic and magnetotransport properties are studied for their nanometric size (~40 nm) grains. X-ray diffraction results show that all samples have single PSMO phase and possess orthorhombic structure. The average grain size of the samples, revealed by scanning electron microscopy (SEM), is found to be 40-50 nm in all the samples. The temperature dependent AC susceptibility, measured through lock-in technique, revealed that the PSMO samples with x=0.40 and 0.50 show a sharp paramagnetic to ferromagnetic (PM-FM) transition at T_C=308 K. However, In PSMO samples with x=0.55 and 0.60, the FM transition temperature is found to decrease slightly to T_C~300 K and the transition width also increases. The most interesting observation in PSMO samples with x=0.55 and 0.60 is the occurrence of a second transition, which occurs at T_C~273 and 255 K for x=0.55 and 0.60 samples, respectively. Furthermore, it is also found that x=0.40 sample shows the highest magnetoresistance (MR) ~12 % at 77 K and H=3 kOe while the value of MR are measured to be ~ 8.0, 4.5 and 3.5 % for x=0.50, 0.55 and 0.60 respectively. The present study also reveals some interesting points related to fundamental physics involved in these compounds.References1.Y. Tokura and Y. Tomioka, J. Magn. Magn. Mater. 200, 1 (1999).2.S. S. Rao, K. N. Anuradha, S. Sarangi, and S. V. Bhat, Appl. Phys. Lett. 87, 182503 (2005).3.D. Akahoshi, et al, Phys. Rev. B, 77 054404 (2008).

9:00 PM - WW8.4

Imaging and Electric Control of Surface and Interface Magnetization in Chromia and Chromia/CoPd Exchange Bias Heterostructures.

Xi He ¹, Ning Wu ¹, Yi Wang ¹, Aleksander Wysocki ¹, Takashi Komesu ¹, Uday Lanke ², Anthony Caruso ³, Elio Vescovo ⁴, Kirill Belashchenko ¹, Peter Dowben ¹, Christian Binek ¹
¹Physics and Astronomy, University of Nebraska-Lincoln, Lincoln, Nebraska, United States, ², Canadian Light Source Inc., saskatoon, Saskatchewan, Canada, ³Department of Physics, University of Missouri, Kansas City, Missouri, United States, ⁴National Synchrotron Light Source, Brookhaven National Laboratory, Upton, New York, United States

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Controlling magnetism and information encoded in magnetic bits is a pillar of modern information technology. Promising spintronic device concepts utilize the electric control of interface and surface magnetization. Controlling magnetic device components via voltage and in the virtual absence of electric current is the key to reduce power consumption while potentially enhancing processing speed, integration density and functionality in comparison with present-day complementary metal-oxide-semiconductor electronics technology. Surface magnetization which is coupled to the bulk antiferromagnetic order parameter is necessarily present in the magnetoelectric antiferromagnet Cr₂O₃ (0001) from symmetry arguments. Macroscopic evidence of this equilibrium boundary magnetization is obtained from integral measurements which include magneto-optical Kerr investigations, superconducting quantum device magnetometry, and spin-polarized photoemission spectroscopy supported by first-principles calculations. Moreover, X-ray magnetic circular dichroism photoemission electron microscopy and magnetic force microscopy provide microscopic, spatially resolved evidence for electrically controlled surface magnetization domains. Since these domains are coupled to the bulk antiferromagnetic domain state, magnetoelectric reversal of the latter through an applied electric field in a permanent magnetic field switches the boundary magnetization together with the antiferromagnetic registration. Using a perpendicular ferromagnetic Pd/Co multilayer deposited on the (0001) surface of a Cr₂O₃ single crystal to form a Cr₂O₃ based exchange bias heterostructure, this unique electrically controlled interface magnetization enables voltage-controlled, reversible, isothermal room-temperature switching of the exchange-bias field between positive and negative values.* This approach offers a promising new route to voltage-controlled spintronic devices, such as non-volatile magnetoelectric memory, which may be viewed as an alternative to other approaches based on multiferroics.* Xi He, Yi Wang, N. Wu, A. N. Caruso, E. Vescovo, K. D. Belashchenko, P. A. Dowben& Ch. Binek, Nature Materials 9, 579 (2010)This work is supported by NSF through Career DMR-0547887, the NSF MRSEC Grant no. 0820521, by the Nebraska Research Initiative (NRI), and by Cottrell Scholar of Research Corporation.

9:00 PM - WW8.5

Role of Defects in the Interfacial Metal-insulator Transition in LaAlO3/SrTiO3.

C. Stephen Hellberg ¹
¹, Naval Research Lab, Washington, District of Columbia, United States

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9:00 PM - WW8.6

Excellent Magneto-transport Properties of La0.7Sr0.3Mn1+dO3-manganese Oxide Composite Films on YSZ Substrates by Aerosol Deposition.

HyoJin Kim ¹, Sang Im Yoo ¹, Young Joon Yoon ², Sung Hwan Cho ²
¹, Seoul national university, Seoul Korea (the Republic of), ², Korea Institute of Ceramic Engineering and Technology (KICET), Seoul Korea (the Republic of)

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9:00 PM - WW8.8

Control of Spontaneous Magnetization and Antiferromagnetic Coupling in Epitaxially Grown Magnetic Oxide Heterostructures of (Ga,Fe)O3 and SrRuO3.

Jihye Lee ¹, William Jo ¹, Christian Meny ², Nathalie Viart ²
¹Physics, Ewha Womans University, Seoul Korea (the Republic of), ², Institute of Physics and Chemistry of Materials of Strasbourg, Strasbourg France

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Antiferromagnetic coupling is a phenomenon by which individual layers in a multi-layered structure consisting of thin magnetic materials are aligned in opposite directions magnetically. Implementation and control of the coupling phenomenon in semiconductors would allow for the development of faster storage media through magnetic recording devices in integrated circuits. Many researchers have paid attention on spin interaction in multilayers because it brings characteristics that cannot be performed in a single layer. It is an essential issue that spins interplay in the interfaces between non-magnetic or magnetic layers in a spin-valve schematic. We have grown b-axis oriented epitaxial (Ga,Fe)O3 (GFO) thin films on (111) oriented SrRuO3 (SRO) ferromagnetic conducting layers by pulsed laser deposition [1,2]. While the magnetization of the GFO layer is along c-axis, the permanent dipole of the SRO layer is along (111) direction. Thus, the easy axis of magnetization of the GFO layer is located on the plane of the thin films. On the other hand, SRO has unique anisotropic properties that arise from the dependence of their magnetic and resistive behaviors on various crystallographic directions in their structure. Magnetic properties of the thin films were measured as a function of temperature and external magnetic field by a superconducting quantum interference magnetometer. Curie temperature of SRO and GFO was measured as 150K and 370K, respectively from the magnetization-temperature (M-T) curves. According to the direction of external magnetic field, the magnetic moment value of the GFO/SRO heterostructures behaved differently. There is a strong temperature dependence of magnetization of the heterostructures at low temperature. The behavior is due to the unique ordering of magnetization of GFO and SRO. If we can grow other combinations of magnetic ordering, we could obtain different coupling phenomena. The unique shape of magnetization-field (M-H) curves depends strongly on the direction of the external magnetic field and configuration of magnetization. [1] M. Trassin, N. Viart, G. Versini, J.-L. Loison, J.-P. Vola, G. Schmerber, O. Crégut, S. Barre, G. Pourroy, J. H. Lee, W. Jo, and C. Mény, Applied Physics Letters 91, 202504 (2007)[2] M. Trassin, N. Viart, G. Versini, S. Barre, G. Pourroy, J. H. Lee, W. Jo, K. Dumesnil, C. Dufour, and S. Robert, Journal of Materials Chemistry 19, 8876 (2009)

9:00 PM - WW8.9

The Origin of Oxygen in Oxide Thin Films - Role of the Substrate.

Thomas Lippert ¹, Martin Esposito ¹, Ivan Marozau ¹, Kazimierz Conder ², Max Doebeli ³, Yi Hu ¹, Marc Mallepell ³, Alexander Wokaun ¹, Christof Schneider ¹
¹ENE, Paul Scherrer Institut, Villigen Switzerland, ²Laboratory for Developments and Methods, Paul Scherrer Institut, 5232 Villigen PSI Switzerland, ³Ion Beam Physics, ETH Zurich, CH-8093 Zurich Switzerland

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2011-04-28 Show All Abstracts

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

WW11: Poster Session: Multiferroic and Nanostructure and Si, Devices

Session Chairs

Thursday PM, April 28, 2011

Salons 7-9 (Marriott)

1:00 AM - WW11: Poster

WW11.14 transferred to WW8.20

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WW9: Multiferroics I

Session Chairs

Mark Rzchowski

Thursday PM, April 28, 2011

Room 2018 (Moscone West)

9:30 AM - **WW9.1

Electric Field Control of Magnetism Using Multiferroics.

Ramamoorthy Ramesh ¹
¹, UCBerkeley, Berkeley, California, United States

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10:00 AM - **WW9.2

Exploring Latent Phase Transitions in Perovskite Oxide Thin Films: Insights from First-principles.

James Rondinelli ¹
¹X-ray Science Division, Argonne National Laboratory, Argonne, Illinois, United States

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10:30 AM - WW9.3

First-principles Investigation of BiFeO3-based Solid Solutions with Enhanced Functional Properties.

Oswaldo Dieguez ¹, Otto Gonzalez-Vazquez ¹, Jacek Wojdel ¹, Jorge Iniguez ¹
¹, ICMAB-CSIC, Bellaterra Spain

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10:45 AM - WW9.4

Exploring Topological Defects in Epitaxial BiFeO₃ Thin Films.

Rama Vasudevan ¹, Yi-Chun Chen ², Hsiang-Hua Tai ², Nina Balke ³, Pingping Wu ⁴, Saswata Bhattacharya ⁴, Long-Qing Chen ⁴, Ying-Hao Chu ⁵, I-Nan Lin ⁶, Sergei Kalinin ³, Nagarajan Valanoor ¹
¹School of Materials Science and Engineering, University of New South Wales, Sydney, New South Wales, Australia, ²Department of Physics, National Cheng Kung University, Tainan City Taiwan, ³The Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, ⁴Department of Materials Science and Engineering, Penn State University, University Park, Pennsylvania, United States, ⁵Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu Taiwan, ⁶Department of Physics, Tamkang University, Tamsui Taiwan

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11:00 AM - WW9

BREAK

11:30 AM - WW9.5

Interfacial Analysis of Morphotropic Boundaries in a Bismuth Ferrite - Lanthanum Aluminate Heterostructure.

Sundaram Sankara Ramakrishnan ¹, Quentin M.Ramasse ², Wen-I Liang ³, Ying-Hao Chu ³, Valanoor Nagarajan ¹, Munroe Paul ¹
¹School of Mateials Science & Engineering, The University of New South Wales, Sydney, New South Wales, Australia, ², SuperSTEM Laboratory, STFC Daresbury, Keckwick Lane,Warrington , WA4 4AD, United Kingdom, ³Dept. Materials Science and Engineering, National Chiao Tung Unviersity, 1001 University Rd., HsinChu, 30010 Taiwan Taiwan

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Recently, multiferroic bismuth ferrite (BiFeO3) has attracted considerable scientific interest because it is both a lead-free material and exhibits ferroelectric ordering coupled with anti-ferromagnetism. The simultaneous presence of switchable ferroelectric and anti-ferromagnetic ordering in a single phase material leads to additional functionality in which ferroelectric polarization can be used to switch magnetic ordering, which opens a new pathway to electrically controllable spintronics. In addition to the parent rhombohedral phase, a tetragonally-distorted perovskite with large spontaneous polarization has also been identified. Using the epitaxial strain between substrate and the BiFeO3 film it is possible to stabilize the tetragonal polymorph, as well the morphotropic phase transition, between the tetragonal and rhombohedral polymorphs. In this present research, multiphase BFO was deposited on a lanthanum aluminate (LaAlO3) substrate using pulsed laser deposition assisted by high pressure RHEED. Cross-sectional high resolution transmission electron microscope studies were carried out using an aberration-corrected dedicated scanning transmission electron microscope (STEM) operating at 100 kV. Electron energy loss spectroscopy (EELS) was also carried out to provide chemical information across the phase boundary. We found that the LaAlO3-BiFeO3 interface was free from any dislocations. However, EELS study across the interface show diffusion of Fe into the LaAlO3 substrate to the order of ~ 2nm. There is also some La diffusion into the BiFeO3, but to shallower depths. It is speculated that this diffusion accommodates misfit strain in this system. Further, the high resolution Z-contrast images confirm the presence of rhombohedral and tetragonal phases adjacent to each other without any dislocations at their interfaces. The EELS studies show a clear change in oxygen K-edge fine structure across the domain wall, which could potentially be linked to relative movement of oxygen octahedra at that boundary and, in turn, explain the giant piezoresponce at the morphotropic phase boundary.

11:45 AM - WW9.6

Strong Room Temperature Magnetism in Highly Resistive, Strained Thin Films of Doped BiFeO3.

Eun-Mi Choi ¹, E. Weal ¹, Suman-Lata Sahonta ¹, H. Wang ², Z. Bi ², J. Xiong ³, M. Blamire ¹, S. Patnaik ¹, Q. Jia ³, J. MacManus-Driscoll ^{1 3}
¹Department of Materials Science, University of Cambridge, Cambridge United Kingdom, ²Department of Electrical and Computer Engineering, Texas A&M University, College Station, Texas, United States, ³MPA-STC and MPA-CINT, Los Alamos National Laboratory, Los Alamos, New Mexico, United States

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12:00 PM - WW9.7

Strain and Electric-field Control of Structural Transition in BiFeO₃.

Weidong Luo ^{1 2}, Ramamoorthy Ramesh ³, Stephen Pennycook ^{1 2}, Sokrates Pantelides ^{2 1}
¹, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, ², Vanderbilt University, Nashville, Tennessee, United States, ³, University of California, Berkeley, California, United States

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BiFeO₃ (BFO) in its ground state is a rhombohedrally distorted perovskite (R phase) and it has a ferroelectric (FE) polarization along the pseudo-cubic [111] direction [1]. BFO under compressive strain of greater than 4% has a highly distorted tetragonal-like structure (T phase) with c/a~1.3, and the FE polarization rotates nearly into the [001] direction [2,3]. Thin films of BFO grown under large compressive in-plane strains (on LaAlO₃ and YAlO₃ substrates) show mixed R- and T phases, and their inter-conversion can be realized by applying an electric- or mechanical field [2]. The structural transition between the T phase and R phase results in a large piezoelectric response, and a large and nonvolatile change in the height of the sample, which make this system attractive for data storage and sensory applications.Here we report the results of a theoretical investigation of the strain and electric-field control of structural transition in BFO using first-principles density-functional theory calculations. The in-plane strains of BFO in the calculations are not limited by experimentally available substrates. We map out the total energy landscape of the BFO system as a function of both in-plane and out-of-plane strain. The complete map of the energy-strain landscape includes one global minimum, associated with the R phase, and one local minimum associated with the T phase. Upon application of an external electric field on BFO, the energy-strain landscape evolves, which modifies the structural phase boundary between the R and T phases, due to the interaction between the electric field and the ferroelectric dipole moment. We obtain the responses of the BFO system as functions of lattice strain, external stress, and electric field. The results of this study extend the current understanding of structural transition in BFO and help optimize the strain, stress, and electric-field boundary conditions for different potential applications.This research was sponsored by the Materials Sciences and Engineering Division, Office of Basic Energy Sciences, U.S. Department of Energy (W. L., S. J. P.), by DOE Grant No. DE-FG02-09ER46554 (S. T. P.), and by the McMinn Endowment at Vanderbilt University (S. T. P.). Computations were performed at the National Energy Research Scientific Computing Center.[1] J. Wang, et al., Science 299, 1719 (2003).[2] R. J. Zeches, et al., Science 326, 977 (2009).[3] A. J. Hatt, N. A. Spaldin, C. Ederer, Phys. Rev. B 81, 054109 (2010).

12:15 PM - WW9.8

Giant Electric-field Control of Spin Waves at Room Temperature in Multiferroic BiFeO₃.

Pauline Rovillain ³, Manuel Bibes ¹, Rogeiro de Sousa ², Yann Gallais ³, Alain Sacuto ³, Marie-Aude Measson ³, Dorothee Colson ⁴, Anne Forget ⁴, Agnes Barthelemy ¹, Maximilien Cazayous ³
³Lab. MPQ, Universite Paris 7, Paris France, ¹UMPhi CNRS/Thales, CNRS, Palaiseau France, ²Dept. of Physics and Astronomy, University of Victoria, Victoria, British Columbia, Canada, ⁴SPEC, CEA, Saclay France

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12:30 PM - WW9.9

Synthesis of Multiferroic YMnO3 Thin Film by Radical Enhanced Atomic Layer Deposition.

Ju Choi ¹, Calvin Pham ¹, Jane Chang ¹
¹Chemical and Biomolecular Engineering, University of California Los Angeles, Los Angeles, California, United States

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Multiferroic materials hold considerable promise because of their potential applications in information storage and spintronics such as magneto-electric sensors, magneto-capacitive devices, and electrically driven magnetic data storage. One of the representative multiferroic materials is yttrium manganese oxide (YMnO3) which exhibits simultaneous ferroelectricity and magnetism. Upon cooling, YMnO3 undergoes a paraelectric–ferroelectric transition at the Curie temperature, and an antiferromagnetic transition at Neel temperature. Therefore, YMnO3 thin film has attracted interest as a candidate for applications in nonvolatile ferroelectric random access memory.To realize the potential of an YMnO3 film in these applications, it must be grown epitaxially and defect-free on a viable substrate. For the hexagonal YMnO3, each magnetic Mn3+ ion is surrounded by five oxygen ions, forming a corner-shared MnO5 bipyramid. YMnO3 shows ferroelectricity along the c-axis due to the tilting of MnO5 bipyramid and a change in distance between O2- and Y3+ ions. Up till now, YMnO3 films have been synthesized largely by molecular beam epitaxy (MBE), pulsed laser deposition (PLD), sputtering and sol-gel method. The growth orientation of YMnO3 filmswas sensitively dependent on the substrates and processing conditions. Thus, still more precise controls at the atomic level are needed in order to get epitaxially grown and defect free thin film on various substrates. YxMnyO3 films were synthesized using a radical enhanced atomic layer deposition (RE-ALD) method at substrate temperature between 210-270°C, using Y(TMHD)3, Mn(TMHD)3, and oxygen atoms as precursors. The growth rate was on the order of 0.15-0.2Å /cycle, which was dependent on substrate temperatures. ALD provides a precise thickness control at the atomic level with low defect density. The as-deposited films, which were amorphous, were annealed by rapid thermal annealing (RTA) between 800-1000°C to achieve crystallinity. The Y/Mn ratio was confirmed by X-ray photoemission spectroscopy (XPS) and the crystal structure was examined by X-ray diffraction. Temperature dependence of the magnetic moment was measured after zero-field-cooling (ZFC) and field–cooling (FC) procedures, with a magnetic field of 100 Oe applied in-plane of the film by a superconducting quantum interference device (SQUID). Specifically, the effect of the Y/Mn ratio on the preferential oriental of YxMnyO3 thin films was delineated. The correlation of the antiferromagnetic and ferroelectric response of YxMnyO3thin films deposited by RE-ALD was shown to be affected by crystal structure, Y/Mn ratio and deposition conditions. Magnetic field induced ferromagnetism was recognized in ferroelectric YxMnyO3 films. The magnetic frustration between in-plane Mn–O layer and Y was quantified as a function of the Y/Mn ratio and different deposition conditions.

12:45 PM - WW9.10

Magnetically Tunable Ferroelectricity in Orthorhombic YMnO₃ Thin Films.

Ignasi Fina ¹, Lourdes Fabrega ¹, Xavier Martí ¹, Florencio Sanchez ¹, Gervasi Herranz ¹, Josep Fontcuberta ¹
¹, Institut de Ciència de Materials de Barcelona CSIC, Barcelona Spain

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WW10: Multiferroics II

Session Chairs

Mark Rzchowski

Thursday PM, April 28, 2011

Room 2018 (Moscone West)

2:30 PM - **WW10.1

Ferroic Phase Transition Sequence in Epitaxial BiFeO3 Thin Films.

Francoise Le Marrec ¹, Helene Toupet ¹, Celine Lichtensteiger ², Brahim Dkhil ³, Michael Karkut ¹
¹LPMC, Universite de Picardie Jules Verne, Amiens France, ²DPMC, Universite de Geneve, Geneva Switzerland, ³SPMS, Ecole Centrale Paris, Châtenay-Malabry France

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3:00 PM - **WW10.2

Twinning-dependent Lattice and Twin-wall Properties in Multiferroic Films.

B. Noheda ¹, C. Daumont ¹, S. Farokhipoor ¹, A. Ferri ¹, J. Wojdel ², J. Iniguez ², B. Kooi ¹
¹Zernike Institute for Advanced Materials, University of Groningen, Groningen Netherlands, ², Institut de Ciencia de Materials de Barcelona (CSIC), Bellaterra Spain

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In multiferroics, the strain induced by the mismatch between the film and the substrate lattice parameters can sometimes be used to tune the film properties with respect to the bulk[1,2]. Bismuth Ferrite, BiFeO₃ (BFO), is one of the few multiferroics that orders above 300 K and, thus, one of the most promising ones[3]. Since the ground state of bulk BFO is rhombohedral (space group R3c), symmetry arguments suggest that the thin films grown on cubic substrates under compressive epitaxial strain should be monoclinic (space group Cm or Cc, depending on whether the O₆ octahedra rotations are clamped by the substrate or not, respectively). Indeed, several authors[4-7] have reported a monoclinic unit cell that is similar to that of strong piezoelectric PbZr_1-xTi_xO₃ with x~0.5[8]. The proposed link between the strong piezoelectricity and the symmetry of the unit cell[9], which allows the polarization to rotate, adds to the interest of BFO films[7].Beyond their intrinsic properties, BFO films are currently receiving renewed attention because of the novel functionalities observed to occur at domain walls (DWs). Indeed, recent works have shown that some BFO DWs are highly conductive[10], that they generate photocurrents[11] and that the DW density controls the magnitude of the (exchange bias) coupling between BFO and other (metallic) layers in complex heterostructures[12]. It is thus of prime importance to achieve control of the domain structures and understand their formation. In addition, it is striking to note the scarcity, and lack of agreement, of experimental information on the atomic structure of the films and its evolution with thickness [4, 6, 13]. We have been able to resolve the monoclinic distortion of BiFeO₃ and TbMnO₃ films on (001)-SrTiO₃ substrates and have observed clear trends in the evolution with thickness of the structure and microstructure. We have shown that the lattice parameters do not result simply from the mismatch with the substrate, but also from the occurrence of a particular twinning that allows for the observed monoclinic distortion. Such an effect provides us with a new degree of freedom for tuning the structural and physical properties of the thin films. Characterization of the domain walls in these films will also be presented. [1] R. Ramesh and N.A. Spaldin, Nature Mat. 6, 21 (2007)[2] J. Wang et al., Science 299, 1719 (2003)[3] G. Catalan and J.F. Scott, Advanced Mat. 21, 2463 (2009)[4] G. Xu et al., Appl. Phys. Lett. 86, 182905 (2005).[5] H. Bea et al. Phil. Magazine Lett. 87, 165 (2007)[6] D.H. Kim et al., Appl. Phys. Lett. 92, 012911 (2008);[7] H. W. Jang et al. Phys. Rev. Lett. 101,107602 (2008).[8] B. Noheda et al. Appl. Phys. Lett. 74, 2059 (1999)[9] L. Bellaiche et al. Phys. Rev.Lett. 84, 5427 (2000)[10] J. Seidel et al., Nature Mat. 8, 229 (2009)[11] S.Y. Yang, Nature Nanotech. 5, 143 (2010)[12] L.W. Martin et al. Nano Letters 8, 2050 (2008)[13] H. W. Jang et al., Adv. Mater. 21, 817(2009)

3:30 PM - WW10.3

Stress-induced R-M_A-M_C-T Symmetry Changes in BiFeO₃ Films.

Hans Christen ¹, Joong Hee Nam ^{1 5}, Hyun-Sik Kim ^{1 4}, Alison Hatt ³, Nicola Spaldin ²
¹, Materials Science and Technology Division, Oak Ridge National Laboratory, Tennessee, United States, ⁵, Korea Institute of Ceramic Engineering and Technology, Seoul Korea (the Republic of), ⁴, Department of Physics, University of Warwick United Kingdom, ³, Molecular Foundry, Lawrence Berkeley National Laboratory, California, United States, ², Department of Materials, ETH Zurich Switzerland

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3:45 PM - WW10.4

Pathway for Enhanced Electro-mechanical Response via Strain Engineering in Multiferroic BiFeO3 Thin Films.

Anoop Damodaran ¹, Lane Martin ¹
¹Materials Science and Engineering, University of Illinois, Urbana Champaign, Urbana, Illinois, United States

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To date, applications requiring strong electromechanical responses in materials – such as nano-positioning, medical ultrasound, sonar, and much more – have generally utilized materials with complex chemistries such as PbZr1-xTixO3 (PZT) and (1-x)[Pb(Mg1/3Nb2/3)O3]-x[PbTiO3] (PMN-PT) near their morphotropic phase boundaries. The steepness of such phase boundaries requires a high degree of compositional control during manufacturing and has made the study of the microscopic origin of enhanced electromechanical properties difficult. In the last few years, however, new single phase systems where similar effects have been observed. One example is that of the multiferroic perovskite BiFeO3 in which application of epitaxial compressive strain (in excess of 4.5%) drives the formation of a so-called “iso-symmetric” phase boundary between a distorted rhombohedral phase to a distorted tetragonal phase. Motivated by the promise this system as a single phase lead-free piezoelectric materials and by the complex nature of the phase competition in this material, we will report on an extensive study of the complex structural nature of the interface between the two coexisting polymorphs in BiFeO3. Epitaxial thin films of BiFeO3 were grown on a variety of substrates that cover a broad range of thin film strains (including YAlO3, LaAlO3, SrTiO3, and DyScO3) using pulsed laser deposition. We have investigated the thickness and temperature dependent evolution of the phase competition in these films through a combination of high-resolution atomic force microscopy (AFM) and detailed X-ray reciprocal space mapping (RSM). AFM scans have revealed highly oriented stripe-like mixtures of the distorted rhombohedral phase and the distorted tetragonal phase as well as dramatic thickness and temperature evolution of this complex structure. Additionally, RSM of the films has revealed previously unreported structural complexity associated with the boundaries in this system – including the presence of additional, intermediate monoclinic phases and significant distortions. We will present detailed structural analysis of all phases present and using a combination of X-ray diffraction, high-resolution AFM, and piezoresponse force microscopy (PFM) studies can uniquely identify the spatial location of each phase across the entirety of the complex, mixed-phase samples. Furthermore, we will present a detailed model of the nature of the nanoscale structural evolution between the dramatically different phases including evidence of an asymmetric boundary structure never before seen. Finally, we will discuss PFM-based switching experiments that indicate our ability to reversibly write pure-tetragonal-like and mixed-phase regions with a high degree of spatial control and will end with a proposed model for the enhanced electromechanical coupling observed in these materials.

4:00 PM - WW10

BREAK

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
¹Department of Materials Science and Engineering, Cornell University, Ithaca, New York, United States, ²Department of Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania, United States, ³Department of Physics, Ohio State University, Columbus, Ohio, United States, ⁴Department of Physics, Pennsylvania State University, University Park, Pennsylvania, United States, ⁵Department of Applied and Engineering Physics, Cornell University, Ithaca, New York, United States, ⁶Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois, United States, ⁷Institute 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, ¹⁰Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey, United States

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We 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 T_N=5.5 K in agreement with bulk unstrained EuTiO₃, whereas the strained EuTiO₃ on DyScO₃ was ferromagnetic with T_C=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).

5:00 PM - WW10.6

Strain-tuning Ferroic Order Parameters in BiFeO₃.

Ingrid Canero-Infante ^{1 2}, Manuel Bibes ¹, Bertrand Dupe ^{2 3}, Audrey Courtial ⁴, Gregory Geneste ², Stephane Fusil ¹, Jean Juraszek ⁴, Sergey Lisenkov ⁵, Laurent Bellaiche ³, Brahim Dkhil ², Agnes Barthelemy ¹
¹UMPhi CNRS/Thales, CNRS, Palaiseau France, ²SPMS Lab., Ecole Centrale, Chatenay-Malabry France, ³Physics Department, University of Arkansas, Fayetteville, Arkansas, United States, ⁴UMR CNRS 6634, CNRS & Universite de Rouen, St Etienne du Rouvray France, ⁵Physics Department, University of Florida, Tamp, Florida, United States

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5:15 PM - WW10.7

Strain-induced Mophotropic Phase Boundary of Multiferroic BiFeO₃ Thin Film on Silicon Substrate.

Wen-I Liang ¹, Chih-Hung Wang ¹, Chun-Yen Peng ¹, Heng-Jui Liu ^{3 2}, Wei-Chen Kuo ⁴, Tai-Bor Wu ², Li Chang ¹, Jenh-Yih Juang ⁴, Darrell Schlom ⁵, Ramamoorthy Ramesh ^{6 7}, Ying-Hao Chu ¹
¹Department of Materials Science and Engineering, National Chiao Tung University, Hsin Chu Taiwan, ³, National Synchrotron Radiation Research Center, Hsin Chu Taiwan, ²Department of Materials Science and Engineering, National Tsing Hua University, Hsin Chu Taiwan, ⁴Department of Electrophsics, National Chiao Tung University, Hsin Chu Taiwan, ⁵Department of Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania, United States, ⁶Department of Materials Science and Engineering, University of California, Berkeley, Berkeley, California, United States, ⁷Department of Phsics, University of California, Berkeley, Berkeley, California, United States

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5:30 PM - WW10.8

Local Ferroelectric Switching of BiFeO₃ Films in Ultra-high Vacuum Down to 4 Unit Cells.

Peter Maksymovych ¹, Mark Huijben ², Stephen Jesse ¹, Nina Balke ¹, Hye Jung Chang ⁴, Albina Borisevich ⁴, Arthur Baddorf ¹, Ramamoorthy Ramesh ³, Sergei Kalinin ¹
¹Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, ²MESA+ Institute for Nanotechnology, University of Twente, Enschede Netherlands, ⁴Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, ³Department of Materials Sciences and Engineering and Department of Physics, University of California Berkeley, Berkeley, California, United States

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Despite years of research, the quantitative trends in the scaling of the switching electric fields in ferroelectric thin films and nanostructures remain controversial, with conflicting conclusions often published on similar material systems. One of the challenges is that traditional ferroelectric hysteresis measurements based on displacement current cannot decouple the electrostatic effect of the dead-layer from the intrinsic size-dependent variation of the switching field. We will show that the solution to this problem can be found in a simultaneous measurement of switching bias and piezoresponse (strain due to applied electric field) of a ferroelectric film. We have applied Band-Excitation Piezoresponse Force Spectroscopy to induce and detect local polarization switching on the surface of BiFeO₃ thin films with a biased metal tip of an atomic force microscope. This technique simultaneously implements resonant enhancement of the electromechanical response and self-consistent monitoring of the changes in the tip-surface contact area. We have measured highly reproducible out-of-plane polarization switching down to film thickness of only ~1.6 nm (approximately four unit-cells) [1]. Quantitative analysis of hundreds of piezoresponse hysteresis loops has further revealed that the switching electric field scaled approximately as 3/4th power of film thickness. Using self-consistent analysis of the variations in the electric field and piezoresponse, we have shown that this surprisingly Kay-Dunn-like scaling is, in fact, an artifact due to the dielectric gaps that significantly reduce applied electric field in the ferroelectric. The normalized switching field, that takes into account the dielectric gap, turned out to be nearly constant for films thinner than ~ 10 nm, consistent with the intrinsic ferroelectric switching mechanism. Extending this methodology onto a statistical analysis of about three thousand hysteresis loops has subsequently revealed spatial heterogeneity in the dielectric gap with sub-10 nm resolution as well as dramatic reduction of the strength of disorder upon reduction of film thickness. Finally, we will discuss how piezoreposne signal can be differentiated from electrostatic tip-surface interaction, which is particularly critical for ultrathin films and ferroelectric materials with small polarization. Reliable measurements of nanoscale ferroelectricity in BiFeO₃ yield the feasibility to device concepts in confined ferroelectric geometries for information storage, spintronics and opto-electronic applications. The measurements were conducted at the Center for Nanophase Materials Sciences sponsored at Oak Ridge National Laboratory by the Division of Scientific User Facilities, U.S. DOE. P. Maksymovych et al. “The Ultrathin Limit and Dead-layer Effects in Polarization Switching of BiFeO₃”, submitted to Nano Lett (2010).

5:45 PM - WW10.9

Mixed Phase BiFeO₃ Thin Films on Silicon Substrates.

Morgan Trassin ¹, John Heron ¹, Ying-Hao Chu ², Qing He ¹, Jinxing Zhang ¹, Carolina Adamo ³, Darrell Schlom ³, Ramamoorthy Ramesh ¹
¹, University of California Berkeley, Berkeley, California, United States, ², National Chiao Tung University, Hsin Chu Taiwan, ³Department of Material Science and Engineering, Cornell University, Ithaca, New York, United States

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WW11: Poster Session: Multiferroic and Nanostructure and Si, Devices

Session Chairs

Friday AM, April 29, 2011

Salons 7-9 (Marriott)

9:00 PM - WW11.1

Probing the Anti-ferromagnet Surface Moment Density on the Bismuth Ferrite Spin Glass Systems.

Khalid Ashraf ¹, Sayeef Salahuddin ¹
¹EECS, UC Berkeley, Berkeley, California, United States

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9:00 PM - WW11.10

Growth of Complex Epitaxial Multi-component Oxide Thin Films and Heterostructures with Strong Anisotropy.

Kazuhiro Endo ¹, Petre Badica ², Hidehito Nanto ¹, Yoshinori Takei ¹, Shunich Arisawa ³, Hirofumi Yamasaki ⁴, Katherine Develos-Bagarinao ⁴, Tamio Endo ⁵
¹, Kanazawa Institute of Technology, Hakusan Japan, ², National Institute of Materials Physics, Bucharest-Magurele Romania, ³, National Institute for Material Science, Tsukuba Japan, ⁴, National Institute of Advanced Industrial Science and Technology, Tsukuba Japan, ⁵, Mie University, Tsu Japan

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9:00 PM - WW11.11

Multiferroicity and Orbital Ordering in Pr0.5Ca0.5MnO3 from First Principles.

Giuseppe Colizzi ^{1 2}, Alessio Filippetti ^{1 2}, Vincenzo Fiorentini ^{1 2}
¹IOM-SLACS, CNR, Cagliari Italy, ²Physics , Cagliari University, Monserrato Italy

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Due to the nontrivial coupling of charge, spin, orbital, and structural degrees of freedom, insulating doped manganites are liable to develop magnetoelectric effects. Both colossal magnetoresistivity and electroresistivity were observed in Pr(1−x)Ca(x)MnO3 near x~0.35-0.5, along with a low-temperature low-symmetry phase. In addition, at half doping, Mn moments order in the AF-CE pattern, made up of zig-zag ferromagnetic chains along the b crystal axis stacked antiferromagnetically along the axes a and c. Charge ordering has been suggested to be the possible midwife of multiferroicity in this system. Two patterns have been envisaged: a Mn 3+ / Mn 4+ checkerboard and a “Zener polaron” state, i.e. a Mn 3+ lattice with charge ordering due to holes sitting on oxygens bridging ferromagnetic Mn's. While both charge ordering would end up being unpolarized, a mixture of the two (basically, a charge-density or orbital-density wave) would lower symmetry so as to develop ferroelectricity, and not just axially, but in the a, b plane.We investigate multiferroicity in Pr0.5Ca0.5MnO3 via the first-principles pseudo-self-interaction-correction density-functional approach, which obtains localization and ordering features straightforwardly essentially at the cost of a standard LSDA calculation. Our findings clearly point to multiferroicity being driven by orbital ordering, and not by charge ordering. In both phases, the 1D ferromagnetic chains show orbital ordering and a gap opening driven by the competition of intra-chain e_g double exchange and inter-chain t_2g superexchange. PCMO in the Pbnm high-temperature structure is paraelectric with checkerboard orbital ordering, and very marginal charge ordering. In the P21nm low-temperature structure, all Mn are charge-equivalent, but essentially no charge ordering appears on oxygens either; a marked Zener-polaron orbital ordering appears instead. The polarization is about 10 microC/cm2, lying in the a,b plane and not just along the a axis. The axial component, orthogonal to the chains, is due to a polar-mode residual of the Pbnm-P21nm structural transition (largely consisting of mere oxygen rotations). In the chain-parallel b direction, ionic contributions are symmetry-compensated, and so the polarization is purely electronic and driven by the cooperative interaction of Zener polaron orbital ordering and AF-CE magnetic ordering.

9:00 PM - WW11.12

Effect of Vanadium Ions on the Functional Properties of Nanocrystalline Zinc Oxide.

Marco A Galvez ¹, Oscar Perales ²
¹, University of Puerto Rico at Mayaguez Department of Physics, Mayagüez, Puerto Rico, United States, ², University of Puerto Rico at Mayaguez Department of Engineering Science and Materials, Mayaguez, Puerto Rico, United States

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9:00 PM - WW11.13

Electrical and Magnetoelectric Properties of PFN on Silicon Substrates.

Camille Garcia ¹, Ricardo Martinez ¹, Kiran Dasari ¹, Ratnakar Palai ^{1 2}
¹, University of Puerto Rico, San Juan, Puerto Rico, United States, ², Institute for Functional Nanomaterials, San Juan, Puerto Rico, United States

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9:00 PM - WW11.15

Understanding the Magneto-electric Coupling of the ε-Fe₂O₃ Polar Magnet.

Marti Gich ¹, Jens Kreisel ², Josep Nogues ^{3 4}, Carlos Frontera ¹, Jose Luis Garcia-Munoz ¹, Anna Roig ¹
¹, Institut de Ciencia de Materials de Barcelona CSIC, Bellaterra Spain, ², Laboratoire des Matériaux et du Génie Physique, CNRS, Grenoble Institute of Technology, MINATEC, Grenoble France, ³, Institució Catalana de Recerca i Estudis Avançats (ICREA) , Bellaterra Spain, ⁴, Centre d’Investigació en Nanociència i Nanotecnologia (ICN-CSIC), Bellaterra Spain

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9:00 PM - WW11.16

Functionally Graded Multiferroic Composites for Ultra-sensitive and Low-noise Magnetic Field Sensors.

Sreenivasulu Gollapudi ¹, Sanjay Mandal ¹, Vladimir Petrov ¹, Gopalan Srinivasan ¹
¹Physics , Oakland University, Rochester, Michigan, United States

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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

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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
¹Department of Materials Science and Metallurgy, University of Cambridge, Cambridge United Kingdom, ²Department of Electrical and Computer Engineering, Texas A and M University, Houston, Texas, United States, ⁴Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States, ⁵Department of Materials Science and Engineering, Pennsylvania State University, State College, Pennsylvania, United States, ³Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, New Mexico, United States

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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
¹Materials Science and Engineering, State Key Lab of New Ceramics and Fine Processing, Tsinghua University, Beijing China, ²Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania, United States

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9:00 PM - WW11.20

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

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Heterostructures 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.

9:00 PM - WW11.21

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

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9:00 PM - WW11.22

Bias-induced Hysteresis and Nanoscale Multiferroic Properties in [Pr(La)]_1-xCa_xMnO₃ 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
¹Dept. of Physics & CICECO, University of Aveiro, Aveiro Portugal, ²DECV & CICECO, University of Aveiro, Aveiro Portugal, ³, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States

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One 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 (Pr_1-xCa_x)MnO₃ or La_1-xCa_xMnO₃ 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 La_0.89Sr_0.11MnO₃ [2] are extended to (Pr_1-xCa_x)MnO₃ and La_0.5Ca_0.5MnO₃ 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).

9:00 PM - WW11.24

Fabrication and Characterization of Novel Room Temperature Relaxor Magneto-electric Multiferroics.

Ashok Kumar ¹, Ram Katiyar ¹, Jim Scott ^{1 2}
¹PHYSICS, University of Puerto rico, San Jaun, Puerto Rico, United States, ², University of Cambridge, Cambridge United Kingdom

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9:00 PM - WW11.25

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
¹Electrophysics, National Chiao Tung University, Hsinchu Taiwan, ³, National Synchrotron Radiation Research Center, Hsinchu Taiwan, ²Materials Science and Engineering, National Chiao Tung University, Hsinchu Taiwan, ⁴Physics, National Cheng Kung University , Tainan Taiwan

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9:00 PM - WW11.27

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

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9:00 PM - WW11.28

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
¹Dept. Materials Science &Engineering, Tsinghua University, Beijing, Beijing, China

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9:00 PM - WW11.29

Magnetic Properties of Self-assembled Epitaxial Nanocomposite Thin Films via a Chemical Solution Approach.

Hongmei Luo ¹, Stacy Baber ¹, Qianglu Lin ¹
¹Chemical Engineering, New Mexico State University, Las Cruces, New Mexico, United States

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9:00 PM - WW11.3

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
¹Department of Electrical and Computer Engineering, Texas A&M University, College Station, Texas, United States, ²Department of Mechanical Engineering, Texas A&M University, College Station, Texas, United States, ³Center for Integrated Nanotechnologies (CINT), Los Alamos National Laboratory, Los Alamos, New Mexico, United States, ⁴Department of Materials Science and Metallurgy, University of Cambridge, Cambridge United Kingdom

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9:00 PM - WW11.31

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
¹Superconductors, 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

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Controlled 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)

9:00 PM - WW11.33

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
¹Department of Physics and Engineering Physics, Tulane University, New Orleans, Louisiana, United States

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Layered 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(SrAl_0.5Ta_0.5O₃)_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 0.02^o 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.

9:00 PM - WW11.34

Synthesis and Characterization of LiNbO₃ Nanostructures.

Debasish Mohanty ¹, Girija Chaubey ¹, Amin Yourdkhani ¹, Gabriel Caruntu ¹, John Wiley ¹
¹Department of Chemistry and Advanced Materials Research Institute, University of New Orleans, New Orleans, Louisiana, United States

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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
¹Mechanical Engineering, University of Puerto Rico At Mayaguez, Mayaguez, Puerto Rico, United States, ²Engineering Science and Materials, University of Puerto Rico, Mayaguez, Puerto Rico, United States, ³Physics, University of Puerto Rico, Mayaguez, Puerto Rico, United States

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9:00 PM - WW11.36

Crystal Structure and Multiferroic Properties of Bi_0.5Sr_0.5FeO_3−δ.

K. Balamurugan ^{1 2}, N. Harish Kumar ¹, P. Woodward ³, Maxim Avdeev ⁴, Santhosh Nagappan Nair ¹
¹Physics, Indian Institute of Technology Madras, Chennai, Tamilnadu, India, ²Department of Chemistry and Biochemistry, Duquesne University, Pittsburgh, Pennsylvania, United States, ³Department of Chemistry, Ohio State University, Columbus, Ohio, United States, ⁴The Bragg Institute, Australian Nuclear Science and Technology Organization, Lucas Heights, New South Wales, Australia

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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
²Graduate School of Engineering Science, Osaka University, Toyonaka Japan, ³Graduate School of Engineering, University of Hyogo, Himeji Japan, ¹Institute for Nanoscience Design, Osaka University, Toyonaka Japan

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BiFeO3 (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
¹Physics, CMU, Mt.Pleasant, Michigan, United States

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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
¹Department of Physics, Indian Institute of Technology, Chennai, TamilNadu, India, ²Department of Physics and Astronomy, Wayne State University, Detroit, Michigan, United States

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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
¹Physics, National Taiwan University, Taipei Taiwan, ⁴Taiwan International Graduate Program, Nano Science and Technology Program, Academia Sinica, Taipei Taiwan, ²Center for Condensed Matter Sciences, National Taiwan University, Taipei Taiwan, ³Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei Taiwan

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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
¹Physics, Indian Institute of Technology, Chennai, TamilNadu, India

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Cobalt 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 2p_3/2), 796.0 eV (Co 2p_1/2), 710.5 eV (Fe 2p_3/2), 724.3 eV (Fe 2p_1/2) and 529.7 eV (O 1s) respectively. The valence states were found to be Co²⁺, Fe³⁺ and O^2-. 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 (H_f) 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 (A_1g + ¹E_g + ³F_2g) characteristic of cubic inverse-spinel structure space group O⁷_h (Fd-3m). Magnetic transport studies were carried out by using vibrating sample magnetometer (VSM). Room temperature saturation magnetization (M_s) was found to be varied from 50.1 to 56.9 emu.g^-1. The observed M_s for nanoparticles was found to be lower than that of the bulk value of CoFe₂O₄ particles (M_s~ 80 emu.g^-1), however it is about 60 % of M_s 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 (ε_r') 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.

9:00 PM - WW11.41

Engineered Perovskite-based Artificial Biferroic Heterostructures.

Ayan Roy Chaudhuri ¹, S. Krupanidhi ²
¹, Max Planck Institute of Microstructure Physics, Halle (Saale) Germany, ²Materials Research Centre, Indian Institute of Science, Bangalore, Karnataka, India

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In 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
¹Electrical and Computer Engineering, University of California Santa Barbara, Santa Barbara, California, United States

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The 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

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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
¹Institute for Inorganic and Analytical Chemistry, Johannes Gutenberg University Mainz, Mainz, RLP, Germany, ²SpinAps, IBM Almaden Research Center, San Jose, California, United States

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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
¹Applied Physics, The Hong Kong Polytechnic University, Hong Kong SAR China

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9:00 PM - WW11.46

Emergence of 90^o 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
¹Materials Science and Engineering, National Chiao Tung University, HsinChu Taiwan, ²Institute of Electronics Engineering, National Tsing Hua University, HsinChu Taiwan, ³Materials Science and Engineering, National Tsing Hua University, HsinChu Taiwan, ⁴, National Synchrotron Radiation Research Center, HsinChu Taiwan, ⁵Physics, National Chen Kung University, Tainan Taiwan

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Multiferroic 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 180^o and 109^o 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 90^o 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 90^o-like DW structure. Conducting behaviors on periodical 90^o DWs are observed by conducting atomic force microscopy. Through atomic layer deposition and electron-beam lithography, natural formed 90^o DW transport behaviors as a function of temperatures and magnetic fields have been probed to understand the fundamental properties of 90^o 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 90^o 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
¹Department of Physics and Electronics, Osaka Prefecture University, Sakai, Osaka, Japan

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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
¹Mechanical Engineering, National University of Singapore, Nil Singapore, ²Materials Science and Engineering, National University of Singapore, Nil Singapore

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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
¹Unite de Catalyse et de Chimie du Solide - CNRS UMR 8181, Universite d'Artois, Lens France

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9:00 PM - WW11.50

Ferroelectric Polarization and Domain Structure in Tetragonal Phase BFO Thin Film.

Jinxing Zhang ¹, R. Ramesh ²
¹Physics and Materials Science, University of California, Berkeley, Berkeley, California, United States, ²Physics, UC Berkeley, Berkeley, California, United States

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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
¹Chemical and Biomolecular Engineering, UCLA, Los Angeles, California, United States, ²Chemistry and Biochemistry, UCLA, Los Angeles, California, United States

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9:00 PM - WW11.52

Excimer Laser Annealing of Piezoelectric Thin Films for MEMS Applications.

Bharadwaja Srowthi ¹, Susan Trolier-McKinstry ¹
¹Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania, United States

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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
¹School of Chemistry, Tel-Aviv University, Tel-Aviv Israel

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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
¹Graduate School of Engineering, Osaka Prefecture University, Sakai, Osaka, Japan

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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 (T_C; 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
¹Material Science and Engineering department, North Carolina State University, Raleigh, North Carolina, United States, ²Mechanical Engineering Department, Georgia institute of technology, Atlanta, Georgia, United States

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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
¹Materials Science & Engineering, Drexel University, Philadelphia, Pennsylvania, United States, ²Code 1512, Naval Undersea Warfare Center, Newport, Rhode Island, United States, ³Code 6360, Naval Research Laboratory, Washington, District of Columbia, United States

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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
¹Organic Materials, Sandia National Laboratories, Albuquerque, New Mexico, United States

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Much 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
¹Physics and Institute for Functional Nanomaterials, University of Puerto Rico, San Juan United States

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9:00 PM - WW11.9

Electron Diffraction Studies of Multiferroic BiMnO_3-δ.

Alexander Eggeman ¹, Paul Midgley ¹, Anthony Cheetham ¹, Chintanami Rao ²
¹Materials Science, University of Cambridge, Cambridge United Kingdom, ²International Centre for Materials Science, JNCASR, Bangalore India

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2011-04-29 Show All Abstracts

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

SeungHyub Baek

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
¹Ciencias de la Tierra y Física de la Materia Condensada, Universidad de Cantabria, Santander, Cantabria, Spain

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Ferroelectric 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
¹Physics, UW - Madison, Madison, Wisconsin, United States, ³, Korea Institute of Science and Technology, Seoul Korea (the Republic of), ²Materials Science and Engineering, UW - Madison, Madison, Wisconsin, United States

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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
¹Department of Physics and Astronomy, University of Nebraska-Lincoln, Lincoln, Nebraska, United States, ²Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States, ³Department of Physics, University of Wisconsin-Madison, Madison, Wisconsin, United States

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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
¹Department of Physics and Astronomy, University of Nebraska-Lincoln, Lincoln, Nebraska, United States, ²Department of Physics, University of Puerto Rico, San Juan, Puerto Rico, United States, ³Kurnakov Institute for General and Inorganic Chemistry, Russian Academy of Sciences, Moscow Russian Federation

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To 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

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In 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.

4:00 PM - WW13:

BREAK

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
¹Department of Materials Science and Engineering, Cornell University, Ithaca, New York, United States, ²Department of Physics and Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania, United States, ⁴School of Applied and Engineering Physics, Cornell University, Ithaca, New York, United States, ³Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania, United States

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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
¹Physics, University of Texas at Austin, Austin, Texas, United States, ²Physics, Arizona State University, Tempe, Arizona, United States, ³Materials Science and Engineering, University of Texas at Dallas, Richardson, Texas, United States

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Perovskite 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
¹Physics, The University of Texas at Austin, Austin, Texas, United States

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We 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).

5:15 PM - WW13.9

Defect Related Magnetism in LaCoO₃ Epitaxial Films.

Virat Mehta ^{1 2}, Yuri Suzuki ^{1 2}
¹Materials Science and Engineering, UC Berkeley, Berkeley, California, United States, ²Material Sciences Division, Lawrence Berkeley National Laboratories, Berkeley, California, United States

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Bulk 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 ~0.8μ_B/Co on STO, and ~0.4μ_B/Co on LAO with the field applied in the in-plane direction. For films grown on LAO, the remnant magnetization (M_r) and the coercive field (H_c) increase with little change to the saturation magnetization (M_s) as the structure relaxes to the bulk. However, films on STO show a gradual decrease of M_s with increasing thickness with little change in M_r and H_c. 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).

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