Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session G17: Focus Session: Improper Ferroelectrics |
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Sponsoring Units: DMP GMAG Chair: Taner Yildirim, NIST Center for Neutron Research Room: 319 |
Tuesday, March 19, 2013 11:15AM - 11:51AM |
G17.00001: Coupling of Magnetic and Ferroelectric Order Parameters in Improper Ferroelectrics Invited Speaker: A. Brooks Harris This talk concerns systems for which the onset of incommensurate magnetic order induces ferroelectricity. I review how Landau theory [1,2] provided a convenient phenomenological explanation of this phenomenon. In the simplest and most frequent scenario, as the temperature is lowered, one first induces collinear incommensurate magetic order. At a lower temperature transition, transverse magnetic components appear and these two different symmetry magnetic order parameters combine to induce ferroelectricity via a trilinear magnetoelectric coupling. I will present several examples of this mechanism, subsequently discussed by Mostovoy[3] within a model of spiral magnetic order. Landau theory also explains [4] a contrasting scenario in which ferroelectric and magnetic can order within a single phase transition as in RbFe(MoO$_4$)$_2$, whose magnetic spiral contradicts the Mostovoy construction, but which Kaplan[5] has subsequently shown to be consistent with a more complete symmetry analysis of microscopic interactions. Other more exotic higher order magnetoelectric couplings, not easily accessible to an analysis of microscopic interactions, are also possible, especially in the presence of nonuniform magnetic order. I close with a few remarks on microscopic models for magnetically induced ferroelectricity. \\[4pt] [1] G. Lawes {\it et al.} PRL 95, 087205 (2005).\newline [2] M. Kenzelmann {\it et al.}, PRL {\bf 95}, 087206 (2005).\newline [3] Mostotovy, PRL {\bf 96}, 067201 (2006).\newline [4] M. Kenzelmann {\it et al.}, PRL {\bf 98}, 267205 (2007).\newline [5] T. Kaplan {\it et al}, PRB {\bf 83}, 174432 (2011) [Preview Abstract] |
Tuesday, March 19, 2013 11:51AM - 12:03PM |
G17.00002: A route to high polarization multiferroics Priya Mahadevan, Hirak Chandra, Kapil Gupta, Ashis Nandy Large ferroelectric polarizations are usually seen in $d^0$ ferroelectrics, while those with a finite d-electron count usually have a polarization which is two orders of magnitude smaller. The route then to high polarization multiferroics, seems quite obvious - examine if we can stabilize the $d^0$ type distortions in finite d-electron systems. The way we went about this was to dope carriers into BaTiO$_3$ and examine if ferroelectricity survived. Considering the example of V doping in BaTiO$_3$, we found that ferroelectricity was strongly stabilized, much stronger that in the undoped limit. Microscopic modeling coupled with ab-initio calculations revealed that part of the stability of the ferroelectric distortions about the V site emerged from first-order Jahn-Teller effects. The dilute doping limit was used to identify some design principles and helped us to design new multiferroics. [Preview Abstract] |
Tuesday, March 19, 2013 12:03PM - 12:15PM |
G17.00003: Exchange Constants from Combined Light and Neutron Scattering Experiments: Application to Magnetoelectric LiMnPO$_{4}$ Cesar J. Calderon Filho, Paulo F. Gomes, Ali F. Garc\'{I}a-Flores, Gaston E. Barberis, David Vaknin, Eduardo Granado Two-magnon Raman scattering is observed in magnetoelectric LiMnPO$_4$, carrying quantitative information on the magnetic interactions between local Mn$^{2+}$ moments. A simulated annealing fitting procedure using these Raman data combined with magnon dispersion curves from neutron diffraction is demonstrated to greatly improve the accuracy and reliability of the determined exchange constants up to at least fifth-nearest neighbors. First-nearest neighbor interactions are shown to be largely dominant in LiMnPO$_4$, ruling out magnetic frustration as a relevant ingredient for this material. This methodology may be instrumental to investigate other magnetoelectric and multiferroic materials as well as superconductors at the border of magnetism, where knowledge of exchange constants without ambiguity is important to pin down the relevant physics. [Preview Abstract] |
Tuesday, March 19, 2013 12:15PM - 12:27PM |
G17.00004: A Model of Magnetic Phase Diagrams of Monoclinic Multiferroics CuO and MnWO$_4$ Guy Quirion, R. Villarreal, M.L. Plumer, M. Poirier, T. Usui, T. Kimura A mean-field Landau-type free energy model developed using symmetry arguments is used to investigate the magnetic field - temperature phase diagrams of monoclinic multiferroics such as CuO and MnWO$_4$. Our analysis supports the necessity of having an intermediate collinear phase between the paramagnetic and magnetoelectric spin spiral phases. The numerical predictions agree well with the experimental phase diagram of CuO (\textbf{H}$\parallel$\textbf{b}) determined recently by high resolution ultrasonic velocity measurments [1] which reveal a new transition at T$_{N3}=230.0$~K associated with collinear ordering, just above the spiral phase at T$_{N2}=229.5$~K. The model also reproduces the magnetic phase diagrams reported for MnWO$_4$ with the applied field along the three principal axes [2] and elucidates the nature of newly identified high-field phases. \\[4pt] [1] R. Villarreal et al., PRL \textbf{109}, 167206 (2012).\\[0pt] [2] H. Mitamura et al., J. Phys. Soc. Japan \textbf{81}, 054705 (2012). [Preview Abstract] |
Tuesday, March 19, 2013 12:27PM - 12:39PM |
G17.00005: Muon spectroscopy as a probe for multiferroic materials Carlos Aristizabal, Alan Drew, Donna Arnold, Finlay Morrison, Laura Nuccio, Viswanathan Mohandoss, Andrei Rotaru, Nicola Morley, Francis Pratt, Sean Giblin, Michael Carpenter Multiferroic magnetoelectrics are materials that exhibit both, ferromagnetic and ferroelectric ordering in the same phase. Thus, they have a spontaneous magnetization that can be manipulated with an applied magnetic field, a spontaneous ferroelectric polarization that can be switched by an applied electric field, and in some cases, there exist some form of coupling between the two order parameters. Such coupling is of great technological importance as it offers the possibility of new multifunctional devices such as transducers, actuators, sensors and memories [1]. Muon spectroscopy (MS) [2] has shown itself to be an extremely versatile and powerful probe of magnetic properties of materials as well as a flexible technique in terms of experimental set up to be able to show magnetic behaviour under an applied electric field. By means of MS and other complementary techniques, I will present, in an entirely new tetragonal tungsten bronze (TTB) class of multiferroic material, a direct coupling in the form of an internal magnetic field that varies hysteretically with an applied electric field. [1] N. A. Spaldin et al., Science 309, 391 (2005) [2] S. J. Blundell, Contemp. Phys. 40, 175, (1999). [Preview Abstract] |
Tuesday, March 19, 2013 12:39PM - 12:51PM |
G17.00006: Magneto--optical properties of complex oxides Peng Chen, Brian Holinsworth, Kenneth O'Neal, Tanea Brinzari, Janice Musfeldt, Nara Lee, Luo Xuan, Sang Cheong, Nyrissa Rogado, Robert Cava, Yaqi Wang, Bernd Lorenz, Steve McGill We investigated the magneto-optical properties of $\alpha$-Fe$_2$O$_3$, frustrated system Ni$_3$V$_2$O$_8$, and rare earth indium oxides like DyInO$_3$ in order to understand the interplay between charge and magnetism. We discovered that hematite appears more red in applied magnetic field than in zero field conditions, an effect that is amplified by the presence of the spin flop transition. Furthermore, magnetic field aligns the spins into fully polarized state and induces optical band gap change in Ni$_3$V$_2$O$_8$. As a consequence, Ni$_3$V$_2$O$_8$ appears more green in 35 T. $\it{f}$ electron excitations in DyInO$_3$ changes dramatically in applied magnetic field because of enormous spin-orbit coupling effect in the rare earth elements. These findings advance our understanding of spin-charge coupling and motivate spectroscopic work on other functional materials under extreme conditions. [Preview Abstract] |
Tuesday, March 19, 2013 12:51PM - 1:03PM |
G17.00007: Effects of rare earth ion size on the stability of the coherent Jahn-Teller distortions in undoped perovskite manganites K.H. Ahn, T.F. Seman, T. Lookman, A. Saxena, A.R. Bishop, P.B. Littlewood We present a theoretical study on the relation between the size of the rare earth ion, often known as chemical pressure, and the stability of the coherent Jahn-Teller distortions in undoped perovskite manganites. Using a Keating model expressed in terms of atomic scale symmetry modes for a simplified two- dimensional model, we show that there exists a coupling between the uniform shear distortion and the staggered buckling distortion within the Jahn-Teller energy term. It is found that this coupling provides a mechanism by which the coherent Jahn-Teller distortion is more stabilized by smaller rare earth ion. We analyze the appearance of the uniform shear distortion below the Jahn-Teller ordering temperature, estimate the Jahn-Teller ordering temperature and its variation among LaMnO3, PrMnO3, and NdMnO3 and obtain the relations between distortions. We find good agreement between theoretical results and experimental data. [Preview Abstract] |
Tuesday, March 19, 2013 1:03PM - 1:15PM |
G17.00008: Magnetic Coupling in the multiferroic hexagonal ErMnO$_{3}$ Huibo Cao, Jun Zhao, Tao Hong, Jie Ma, Bryan Chakoumakos Hexagonal ErMnO$_{3}$ is one of the rare earth manganites RMnO$_{3}$ and has attracted renewed interest due to its multiferroic properties. Understanding the coupling between spin, charge, and lattice degrees of freedom is crucial to explore and design strong magnetic-ferroelectric coupled materials. We measured the crystal and magnetic structures of ErMnO$_{3}$ at selected temperatures and magnetic fields by single crystal neutron diffraction. Combined with planned inelastic neutron scattering measurements, the magnetic-magnetic and magnetic-lattice interactions will be discussed. [Preview Abstract] |
Tuesday, March 19, 2013 1:15PM - 1:27PM |
G17.00009: Vortex interactions and formation of vortex networks in hexagonal YMnO$_3$ Sergey Artyukhin, Karin M. Rabe, David Vanderbilt, Maxim Mostovoy Multiferroic materials with their coexisting magnetic and ferroelectric orders are of pressing interest for spintronics and information storage technology. In hexagonal manganites there is an additional order, structural trimerization, which strongly interacts with both charge and spin degrees of freedom [1,2]. This results in the clamping of structural, ferroelectric and antiferromagnetic domain walls and gives rise to the appearance of multiferroic vortices [3,4,2]. Motivated by the recent experiments of the group of S-W. Cheong visualizing vortex networks formed in YMnO$_3$ at different cooling rates, we use Landau-type theory and electronic structure calculations to study vortex network formation and interpret experimental observations. Our results emphasize the importance of strains for the understanding of vortex interactions in this material.\newline [1] C.J. Fennie, K.M. Rabe, PRB 72, 100103 (2005)\newline [2] S. Artyukhin et al., arXiv:1204.4126\newline [3] T. Choi et al., Nature Materials 9, 253 (2010)\newline [4] M. Fiebig et al., Nature 419, 818 (2002) [Preview Abstract] |
Tuesday, March 19, 2013 1:27PM - 1:39PM |
G17.00010: Interplay of octahedral distortions in electronic and structural phase transitions in $ABO_{3}$ perovskites Prasanna V. Balachandran, James M. Rondinelli In this work, we investigate group-subgroup relationships afforded to $ABO_{3}$ perovskites from combinations of $BO_{6}$ distortions -- bond stretching and bond angle rotations -- with the objective of identifying new pathways for tuning their properties through electron-lattice interactions. Using nickelate and bismuthate perovskite compounds as a template, we decompose their low-symmetry structures into orthonormal symmetry-breaking lattice modes of the parent cubic space group. Statistical analysis of mode decomposition data uncovers previously unappreciated relationships between microscopic octahedral distortion modes and macroscopic physical properties. Finally, we propose novel crystal engineering strategies to study perovskites near phase boundaries that are otherwise extremely difficult to probe experimentally. [Preview Abstract] |
Tuesday, March 19, 2013 1:39PM - 1:51PM |
G17.00011: Cation Ordering in Layered Nickelates Brittany Nelson-Cheeseman, Hua Zhou, Antonio Cammarata, Jason Hoffman, Prasanna Balachandran, James Rondinelli, Anand Bhattacharya The single layer Ruddlesden-Popper nickelates present a model system to understand how the effects of digital dopant cation ordering may affect the properties of 2-dimensional conducting sheets. We investigate the effects of aliovalent A-site cation order on LaSrNiO$_{4}$ films. Using molecular beam epitaxy, we interleave full layers of SrO and LaO in a series of chemically equivalent films, varying the pattern of SrO and LaO layers relative to the NiO$_{2}$ layers. Through synchrotron surface x-ray diffraction and Coherant Bragg Rod Analysis (COBRA), we directly investigate the A-site cation order and the resulting atomic displacements for each ordering pattern. We correlate these results with theoretical calculations and transport measurements of the layered nickelate films. [Preview Abstract] |
Tuesday, March 19, 2013 1:51PM - 2:03PM |
G17.00012: Total energy calculations of correlated electron compounds: theory and application to rare earth nickelates Hyowon Park, Andrew Millis, Chris Marianetti We use density functional theory (DFT) plus dynamical mean field theory (DMFT) method, along with DFT+U and Hartree-Fock methods to compute the electronic energy as a function of crystal structure for rare earth nickelates. We show that full charge self-consistency can be essential for obtaining qualitative agreement with experiment and that the choice of double counting correction has an important effect on the energy. Furthermore, the precise definition (projector vs Wannier) of the correlated d-orbitals has a minimal effect. We show that charge self-consistent DFT+DMFT, as opposed to DFT+U, is critical to describing the magnetic-insulator to paramagnetic-metal phase boundary in the rare earth nickelate phase diagram. [Preview Abstract] |
Tuesday, March 19, 2013 2:03PM - 2:15PM |
G17.00013: Neutron Scattering in Multiferroics Ba$_{2}$CoGe$_{2}$O$_{7}$ Minoru Soda, Takatsugu Masuda, Masashige Matsumoto, Severian Gvasaliya, Martin Mansson, Andrey Zheludev Ba$_{2}$CoGe$_{2}$O$_{7}$ having the noncentrosymmetric crystal structure shows a staggered antiferromagnetic structure in the (001) plane below $T_{N}$=6.7 K. In the magnetically ordered state, a ferroelectric polarization is observed even at a magnetic field $H$=0, and largely enhanced under $H$. In Ba$_{2}$CoGe$_{2}$O$_{7}$, Murakawa and co-workers have shown that the ferroelectricity is induced by the spin-dependent $d$-$p$ hybridization mechanism. Furthermore, the 4 meV excitation, which is an electric-active mode through the coupling between spin and electric-dipole, was observed in the electromagnetic wave absorption. In the present study, the neutron scattering measurements were carried out in Ba$_{2}$CoGe$_{2}$O$_{7}$ under the magnetic field. We found one acoustic and two optical modes in zero field, which are reasonably reproduced by the extended spin wave theory. Furthermore, our result indicates that the anisotropy of the magnetic moments also connects with the multiferroic property of Ba$_{2}$CoGe$_{2}$O$_{7}$. [Preview Abstract] |
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