Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session V37: Focus Session: Complex Oxide Thin Films -- Multiferroics and Tunneling |
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Sponsoring Units: DMP GMAG Chair: Stuart Wolf, University of Virginia Room: E147-E148 |
Thursday, March 18, 2010 8:00AM - 8:36AM |
V37.00001: Perspectives of Ferroelectric and Multiferroic Tunnel Junctions Invited Speaker: Tunnel junctions are electronic devices in which current-carrying electrons can quantum-mechanically be transmitted between two metal electrodes across a very thin insulating barrier layer. So far almost all the existing tunnel junctions were based on non-polar dielectrics. An exciting possibility to extend the functionality of tunnel junctions is to use a ferroelectric insulator as a barrier to create a ferroelectric tunnel junction (FTJ). [1] The key property of FTJ is tunneling electroresistance (TER) that is a change in the electrical resistance of FTJ with reversal of ferroelectric polarization. Functional properties of FTJ can be further extended by ferromagnetic metal electrodes to make a multiferroic tunnel junction (MFTJ). In such a MFTJ tunneling magnetoresistance (TMR) can be controlled by ferroelectric polarization of the barrier. [1] Thus, MFTJs represent four-state resistance devices that can be controlled both by electric and magnetic fields due to the coexistence of TER and TMR effects. This talk will address the physics of FTJs and MFTJs based on our recent model and first-principles calculations. In particular, we will discuss the effect of a thin non-polar dielectric layer at the FTJ interface that leads to giant values TER, which may be relevant to recent experimental observations. \\[4pt] [1] E. Y. Tsymbal and H. Kohlstedt, \textit{Science}\textbf{313}, 181 (2006). [Preview Abstract] |
Thursday, March 18, 2010 8:36AM - 8:48AM |
V37.00002: Magneto-electric and strain coupling in ferromagnetic manganite thin films grown on ferroelectric substrates Norbert Nemes, Federico Mompean, Alicia De Andres, Nevenko Biskup, Aurora Alberca, Mar Garcia-Hernandez, Cristina Visani, Javier Tornos, Fabian Cuellar, Mirko Rocci, Flavio Bruno, Jacobo Santamaria We study the magneto-electric coupling in La$_{0.67}$Ca$_{0.33}$MnO$_{3}$ (LCMO) and La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ (LSMO) thin films with thickness between 5 and 20 nm grown on ferroelectric BaTiO$_{3}$ (BTO) or Pb(Mg$_{0.33}$Nb$_{0.67}$)$_{0.72}$Ti$_{0.28}$O$_{3}$ (PMNT) single crystal substrates. We measure the temperature, magnetic and electric field dependent magnetization and magnetoresistance of the manganite thin films. In bulk, LCMO is more prone to disorder induced phase segregation and a metal- insulator transition than LSMO. Nevertheless, the substrate- strain induced changes in LSMO have been more extensively reported. We report large magnetoresistance changes of LCMO thin films corresponding to the structural phase transitions of the BTO substrate. [Preview Abstract] |
Thursday, March 18, 2010 8:48AM - 9:00AM |
V37.00003: Electrically-induced magnetic reconstruction at the manganite/ferroelectric interface J.D. Burton, Evgeny Tsymbal The control of magnetization via the application of an electric field, known as magnetoelectric coupling, is among the most fascinating and active research areas today. In addition to fundamental scientific interest, magnetoelectric effects may lead to new device concepts for data storage and processing. Here we explore a different type of magnetoelectric effect at a ferromagnetic-ferroelectric interface: magnetic reconstruction induced by switching of electric polarization.[1] We demonstrate this effect using first-principles calculations of a La$_{1-x}A_{x}$MnO$_{3}$/BaTiO$_{3}$ (001) interface, where $A$ is a divalent cation. By choosing the doping level $x$ to be near a transition between magnetic phases we show that the reversal of the ferroelectric polarization of BaTiO$_{3}$ leads to a change in the magnetic order at the interface from ferromagnetic to antiferromagnetic. This predicted electrically induced magnetic reconstruction at the interface represents a substantial interfacial magnetoelectric effect. [1] J. D. Burton and E. Y. Tsymbal, Phys. Rev. B \textbf{80}, 174406 (2009). [Preview Abstract] |
Thursday, March 18, 2010 9:00AM - 9:12AM |
V37.00004: Low-Temperature Magnetic Force Microscopy studies of LCMO and LSMO films on BTO substrates Alfred Lee, Alex de Lozanne, Xavier Moya, Neil D. Mathur Strong strain-mediated magnetoelectric coupling arises at epitaxial planar interfaces, e.g. between ferromagnetic films and ferroelastic substrates [1]. Discontinuous changes in strain at the $\sim $190 K rhombohedral-orthorhombic transition of a ferroelastic BaTiO$_{3}$ substrate produce discontinuous changes in the macroscopic magnetizations of ferromagnetic epitaxial thin films of La$_{0.7}$Ca$_{0.3}$MnO$_{3}$ or La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ [1]. In order to explore the microscopic changes through this transition, we will present magnetic force microscopy data for the two systems above and below $\sim $190 K. [1] M. K. Lee \textit{et al.}, \textit{Appl. Phys. Lett.} \textbf{77} (2000) 3547; W. Eerenstein \textit{et al.}, \textit{Nature Materials} \textbf{6} (2007) 348 [Preview Abstract] |
Thursday, March 18, 2010 9:12AM - 9:24AM |
V37.00005: Local enhancement of magnetoelectric coupling observed using magnetic force microscopy Massimo Ghidini, Neil D. Mathur Poled multilayer capacitors (MLCs) show strain-mediated magnetoelectric coupling [1,2], but the microscopic details are unknown. By recording magnetic force microscopy (MFM) images at a polished surface in zero electric field, we show that the magnetic domain configuration of the Ni-based electrodes may be switched by electric-field history. By contrast, electric-field history has nominally no effect on the macroscopic magnetization measured in zero electric field. This suggests that miniaturized systems could show non-volatile converse magnetoelectric effects even if bulk data are not promising, thus extending the range of candidate materials systems for electric-write magnetic-read data storage. \\[4pt] [1] C. Israel, N. D. Mathur and J. F. Scott, \textit{Nature Materials} \textbf{7} (2008) 93 \\[0pt] [2] C. Israel, S. Kar-Narayan and N. D. Mathur, \textit{Appl. Phys. Lett.} \textbf{93} (2008) 173501 [Preview Abstract] |
Thursday, March 18, 2010 9:24AM - 9:36AM |
V37.00006: Dielectric and Magnetic Properties of Bi$_{1-x }$Sm$_{x}$FeO$_{3}$ (0$\le $x$\le $1) Ricardo Melgarejo, Venkata Puli, Neeraj Panwar, Reji Thomas, Ram Katiyar Multiferroic materials like BiFeO$_{3}$ (BFO) have recently gained worldwide attention due to their applications in nonvolatile memories, spintronics, sensors, and micro mechanical systems (MEMS). BiFeO$_{3}$ is a naturally occurring multiferroics, however, the large leakage current has hampered its practical applications. To circumvent this problem generally, substitution is carried out at Bi and Fe sites. We have doped samarium (Sm) at Bi-site in BFO. Thin films were grown on Pt/Ti/SiO$_{2}$ /Si substrates by spin coating method. XRD patterns showed well-grown perovskite structure with polycrystalline nature. Dielectric properties, leakage current, and magnetic properties were systematically studied. A correlation between these properties will be presented. [Preview Abstract] |
Thursday, March 18, 2010 9:36AM - 9:48AM |
V37.00007: Theory of magnetoelectric switching in spiral magnets Andrea Scaramucci, Thomas Kaplan, Maxim Mostovoy We study magnetoelectric switching phenomena in multiferroic materials where electric polarization is induced by a spiral spin ordering. Recent experiments showed that electric polarization of ZnCr$_{2}$Se$_{4}$ and Eu$_{0.55}$Y$_{0.45}$MnO$_{3}$ can be manipulated by an applied magnetic field and that the efficiency of the magnetoelectric switching, i.e. the polarization reversal induced by reversing the direction of magnetic field, strongly depends on the strength of the field and the path along which it changes its direction. We present the results of analytical and numerical studies of deformations of the spiral states produced by the combined effect of an applied magnetic field and magnetocrystalline anisotropy and provide a simple picture explaining the rich variety of the observed behaviors. We also study clamping between ferromagnetic and ferroelectric domain walls that controls magnetoelectric switching in the conical spiral magnet CoCr$_{2}$O$_{4}$. [Preview Abstract] |
Thursday, March 18, 2010 9:48AM - 10:00AM |
V37.00008: \textit{In situ} stoichiometry control using reflection high energy electron diffraction generated x-rays Cameron Keenan, Sandeep Chandril, Thomas H. Myers, David Lederman One major challenge in the stoichiometric growth of complex oxides, such as YMnO$_{3}$, is the control of the relative compositions of the constituent materials. Desirable properties of oxide materials, such as ferroelectricity, are highly dependent upon material stoichiometry, making stoichiometry control an important issue. While RHEED (\underline {R}eflection \underline {H}igh \underline {E}nergy \underline {E}lectron \underline {D}iffraction) analysis is typically used as a qualitative tool, RHEED generated x-rays can be used to give quantitative compositional information. The relative compositions of Y and Mn in MBE grown YMnO$_{3}$ samples were studied using the grazing exit x-rays generated by RHEED electrons. Comparing the results with RBS characterization suggested that the technique has the potential for real-time compositional analysis. [Preview Abstract] |
Thursday, March 18, 2010 10:00AM - 10:12AM |
V37.00009: Ferroic Coupling in Layered Perovskites from First Principles Turan Birol, Nicole Benedek, Craig Fennie Antiferrodistortive SrTiO$_3$ can be driven ferroelectric with a modest amount of biaxial strain. The n = 1 Ruddlesden-Popper remains paraelectric and undistorted for the same strain state. Elucidating the manner in which ferroic instabilities emerge as the number of perovskite blocks, n, increases is a fundamentally interesting challenge in its own right, yet a proper understanding could open new avenues in materials design. Combining first-principles calculations and symmetry arguments, we study the effect of strain (or pressure) and dimensionality on ferroic coupling in the layered Sr-Ti-O perovskites. [Preview Abstract] |
Thursday, March 18, 2010 10:12AM - 10:24AM |
V37.00010: Giant positive magnetoresistance in non-magnetic Au/YSZ/Si heterostructures Tianliang Qu, Yonggang Zhao, Jiawei Mei, Jia Li, Xiao Liu There is an on-going interest in the giant positive magnetoresistance (GPMR) effects in nonmagnetic materials because of their importance for the understanding of carrier transport in magnetic fields as well as applications. We report on the nonlinear current-voltage (I-V) behavior and GPMR in the Au/YSZ (Yttria-stabilized zirconia)/Si heterostructures fabricated by depositing YSZ film on silicon substrate by pulsed laser deposition. The I-V curves of the heterostructures show a rectifying property and follow the Fowler-Nordheim (FN) tunneling behavior for the larger forward bias voltages. The GPMR of the samples increases with decreasing temperature and exceeds 100000{\%} at 20 K with a voltage of +4 V and a magnetic field of 7 T. It also shows anisotropy with the magnetic field. Analysis of the results suggests that the GPMR effect originates from the impact of magnetic field on the trap assisted Fowler-Nordheim (FN) tunneling of the heterostructures. [Preview Abstract] |
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