Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session B36: Focus Session: Bulk Properties of Complex Oxides  Manganite Multiferroics 
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Sponsoring Units: DMP GMAG Chair: Hari Srikanth, University of South Florida Room: E146 
Monday, March 15, 2010 11:15AM  11:27AM 
B36.00001: Emerging MagnetoElectric Properties in Orthorhombic Nd$_{1x}$Y$_{x}$MnO$_{3}$ Sven Landsgesell, Karel Prokes, Bachir Ouladdiaf, Bastian Klemke, Dimitri Argyriou We have synthesized single crystals of the solid solution Nd$_{1x}$Y$_{x}$MnO$_{3}$ and we have investigated them using dielectric constant, ferroelectric polarization and single crystal neutron diffraction. We find that with increasing x the Atype magnetic ordering of Mn3+ ions is suppressed and for x $>$ 0.45 a cycloidal magnetic order is found. For these compositions we find an emergent ferroelectric polarization along the caxis. In the region of 0.35 $<$ x $<$ 0.45 we find a complex coexistence of collinear Atype and incommensurate magnetism. This suggests that the transition from collinear to cycloidal (multiferroic) ground state with x is first order like. [Preview Abstract] 
Monday, March 15, 2010 11:27AM  11:39AM 
B36.00002: Model for twin electromagnons and magnetically induced oscillatory polarization in multiferroic RMnO$_3$ Rog\'{e}rio de Sousa, Markku Stenberg We propose a model [1] for the pair of electromagnon excitations observed in the class of multiferroic materials RMnO$_3$ (R is a rareearth ion). The model is based on a harmonic cycloid ground state interacting with a zoneedge magnon and its twin excitation separated in momentum space by two times the cycloid wave vector. The pair of electromagnons is activated by cross coupling between magnetostriction and spinorbit interactions. Remarkably, the spectral weight of the twin electromagnon is directly related to the presence of a magnetically induced oscillatory polarization in the ground state. This leads to the surprising prediction that TbMnO$_3$ has an oscillatory polarization with amplitude 50 times larger than its uniform polarization. \\[4pt] [1] M.P.V. Stenberg and R. de Sousa, Phys. Rev. B {\textbf 80}, 094419 (2009) (Editors' suggestion). [Preview Abstract] 

B36.00003: ABSTRACT WITHDRAWN 
Monday, March 15, 2010 11:51AM  12:03PM 
B36.00004: Microscopic theory on the electromagnetic phase diagram for multiferroic RMnO$_3$: Atype, incommensurate spiral, and Etype spin phases Nobuo Furukawa, Masahito Mochizuki We have theoretically studied the electromagnetic phase diagram for the multiferroic Mn perovskites ($R$MnO$_3$), which exhibits successive three magnetic phases of Atype, incommensurate spiral, and E type spin orderings at low temperatures. We first show that bond alternations in the $J_1$$J_2$ model successfully reproduce successive transitions among above three phases. We then studied the diagram by using a realistic spin model of the Mn perovskites, which contains the spin exchanges coupled with phonons, the DM interactions, and the singleion spin anisotropies. This realistic model enables us to solve many puzzling issues of the diagram such as spin spiralplane flop between $ab$ to $bc$, anomalous temperature dependence of electric polarizations, and ferroelectricity in the Etype phase. Comparison between above two studies highlights the roles of each interaction and anisotropy on the related intriguing phenomena. [Preview Abstract] 
Monday, March 15, 2010 12:03PM  12:15PM 
B36.00005: Writing and reading chiral domains in multiferroic DyMnO$_3$ using soft Xrays E. Schierle, V. Soltwisch, D. Schmitz, R. Feyerherm, A. Maljuk, F. Yokaichiya, D.N. Argyriou, E. Weschke The structure and dynamics of domains and domain walls are at the heart of any device that utilizes the properties of a ferroic material. Multiferroics, materials that exhibit a strong coupling between ferroelectric and magnetic order, offer the possibility of rich and complex domain arrangement that can be exploited for spintronics and magnetoelectric devices. However, due to the complex magnetic order that is found in multiferroics, imaging of domains of a composite ferroic nature is challenging. We report on soft Xray studies of the multiferroic material DyMnO$_{3}$, where regions of opposite ferroelectric polarization correspond to magnetic domains of opposite chirality due to the spindriven nature of ferroelectricity. With local charging induced by the Xray beam via the photoelectric effect we are able to imprint a pattern of chiral magnetic domains on the surface of a single crystal. We utilize the circular dichroism in magnetic Xray diffraction caused by the cycloidal magnetic ordering of the Dy4f moments to read out the chiral domains, taking further advantage of the large enhancement at the Dy$M_5$ resonance. The method we describe here suggests a novel approach to control and image domains and domain walls in multiferroic materials. [Preview Abstract] 
Monday, March 15, 2010 12:15PM  12:27PM 
B36.00006: Polarized Inelastic Neutron Scattering study of TbMnO$_3$ Rolando Valdes Aguilar, I. Cabrera, Y. Zhao, C. Broholm, N.P. Armitage, H.D. Drew, SW. Cheong, C.L. Zhang Low energy collective excitations in TbMnO$_3$ were examined using polarized inelastic neutron scattering. By probing spin flip and nonspinflip excitations with a guide field along wave vector transfer, Q, we separated the magnetic and vibrational components of excitations at high symmetry points in the Brillouin zone. We report signatures of coupled magnonphonon excitations in the ferroelectricspiral state, which disappear in the paramagnetic phase. These results will be discussed in terms of current models of electromagnons in the \textit{R}MnO$_3$ multiferroic family. [Preview Abstract] 
Monday, March 15, 2010 12:27PM  12:39PM 
B36.00007: Ferroelectric and structural domains in multiferroic RMnO$_{3}$ (R=rare earths) Y. Horibe, T. Choi, H.T. Yi, Weida Wu, S.W. Cheong Hexagonal RMnO$_{3}$ (R=rare earths) exhibits a unique improper ferroelectricity induced by structural trimerization. Although intimate coupling between ferroelectric and antiferromagnetic domains was reported at low temperatures [1], the structural domains related to ferroelectric have not been wellstudied. In this talk, we will report the relationship between ferroelectric and structural domains in RMnO$_{3}$, obtained from the results of our transmission electron microscopy and scanning probe microscopy. Characteristic structural/ferroelectric domain patterns are clearly observed at room temperatures. The successive phase transitions in RMnO$_{3}$ are suggested to play a crucial role in the domain formation. \\[4pt] [1] M. Fiebig \textit{et al.}, Nature 419, 818 (2002). [Preview Abstract] 
Monday, March 15, 2010 12:39PM  12:51PM 
B36.00008: Low Temperature Local Structure of Multierroic of ReMn$_{2}$O$_{5}$ Peng Gao, A. Masadeh, T.A. Tyson, Th. Proffen, S. Goche, S.W. Cheong The temperature dependent structure of the REMn$_{2}$O$_{5 }$ (REe=rare earth) system has been examined by the Neutron and Xray pair distribution function method based on highq data. Comparisons with Rietveld and XAFS measurements will be made. The detailed temperature dependent structure on multiple length scales will be presented. [Preview Abstract] 
Monday, March 15, 2010 12:51PM  1:03PM 
B36.00009: Magnetic Ordering in Multiferroics Eu0.3Y0.7MnO3. Fabiano Yokaichiya, Manfred Reehuis, Andrey Maljuk, Dimitri Argyriou, Maria Teresa Fernandes Diaz The recent interest in the study of perosvkitemanganite RMNO3 (with R=rare earth) is due to the observation of the ferroeletric transitions that are concomitant with complex ordering of Mn 3d spins. In order to clarify the correlation between the magnetic transitions of the Mn 3d spins with the ferroelectric transition, we investigated the magnetic structure of the perovskite Eu0.7Y0.3MnO3 without the influence of the 4f magnetic moment of the rare earth ion. It was observed, below 30 K, a cycloid magnetic structure in the ab plane which drives the emergent ferroelectricity via the antisymmetric DzyaloshinskiMoriya interaction.This magnetic ordering provides the magnetic origin for the ferroelectricity polarization parallel to the aaxis.Moreover, between 30 and 50 K, an additional magnetic phase with a collinear sinusoidal magnetic structure was observed. [Preview Abstract] 
Monday, March 15, 2010 1:03PM  1:15PM 
B36.00010: Origin of Electric Field Induced Magnetization in Multiferroic HoMnO$_{3}$ B.G. Ueland, J.W. Lynn, M. Laver, Y.J. Choi, S.W. Cheong We have performed polarized and unpolarized small angle neutron scattering experiments on single crystals of HoMnO$_{3}$ and have found that an increase in magnetic scattering at low momentum transfers begins upon cooling through temperatures close to the spin reorientation transition at $T_{SR} \quad \approx $ 40 K. We attribute the increase to an uncompensated magnetization arising within antiferromagnetic domain walls. Polarized neutron scattering experiments performed while applying an electric field show that the field suppresses magnetic scattering below $T \quad \approx $ 50 K, indicating that the electric field affects the magnetization via the antiferromagnetic domain walls rather than through a change to the bulk magnetic order. http://arxiv.org/abs/0909.0198v1 [Preview Abstract] 
Monday, March 15, 2010 1:15PM  1:27PM 
B36.00011: Novel Striped Multiferroic Phases in HoleDoped Manganites Shuhua Liang, Shuai Dong, Elbio Dagotto After the discovery of a socalled ``spinorthogonal stripe'' (SOS) phase in models for quarterdoped hole manganites [1], our group carried out additional computational work at other doping fractions to search for analogous multiferroic phases. Here we report the discovery of similar SOS phases at several hole dopings $x=1/N$ $(N=3,5,6...)$ using a double exchange model with spin frustration, and applying variational and Monte Carlo techniques. The full phase diagram created by varying electronlattice and superexchange couplings also contains an exotic $C_{x}E_{1x}$ phase. The new SOS$_{x}$ phases are intuitively explained via a rotation from the $C_{x}E_{1x}$ zigzag spin configuration. This creates stripes separating domains containing orthogonal spins. Because of the DzyaloshinskiiMoriya interaction, it is conjectured that these SOS states should be ferroelectric as well. For $N$ even the spin states are similar to $N$ odd but there is a cancellation of the net ferroelectric moment. \\[4pt] [1] Shuai Dong {\it et al.}, Phys. Rev. Lett. {\bf 103}, 107204 (2009). [Preview Abstract] 
Monday, March 15, 2010 1:27PM  1:39PM 
B36.00012: Nanoscale characterization of the ferroelectric domain structure in multiferroic RMnO$_{3}$ (R: rare earths) Taekjib Choi, Yoichi Horibe, HeeTaek Yi, Young Jai Choi, Weida Wu, SangWook Cheong Recent progresses in fabrication and nanoscale characterization of high quality complex oxides have driven a significant understanding of underlying physics in the field of multiferroic and ferroelectric materials. The hexagonal manganites, RMnO$_{3}$ (R: rare earths), have been extensively studied because of the rich physics of the hexagonal system with both longrange electric and magnetic orders. In this work, intriguing ferroelectric domain structures coupled intimately with structural domains are spatially resolved using scanning probe microscopy. In addition, we explored the domain growth behavior by external stimulus. Our results provide critical insights into understanding the origin of remarkable magnetoelectric coupling in the hexagonal RMnO$_{3}$. [Preview Abstract] 
Monday, March 15, 2010 1:39PM  1:51PM 
B36.00013: Magnetic phase competition in multiferroic hexagonal Ho$_{1x}$Y$_{x}$MnO$_{3}$ Jagath C. Gunasekera, Yuan Wang, Tom Heitmann, Owen P. Vajk Hexagonal RMnO$_{3}$ compounds are both ferroelectric and magnetic, a combination known as multiferroic. We have grown singlecrystal samples of Ho$_{1x}$Y$_{x}$MnO$_{3}$ at a variety of compositions to study the role of the rareearth ion in RMnO$_{3}$. Previous neutron scattering measurements of YMnO$_{3}$ have revealed quasielastic scattering around the (1,0,L) position below T$_N$ with inplane correlations and no outofplane correlations [1]. These results have been attributed to phase competition between a 2D KosterlitzThouless phase and 3D N\'{e}el order. We find similar quasielastic scattering in Ho$_{1x}$Y$_{x}$MnO$_{3}$ samples, but the quasielastic scattering shows both inplane and outofplane correlations below T$_N$. Magnetic Bragg scattering occurs at either the (1,0,0) or (1,0,1) positions depending on the phase, and quasielastic scattering is located at either the (1,0,1) or (1,0,0) position at whichever location the Bragg scattering is not. These results suggest that the observed quasielastic scattering may be related to competition not between 2D and 3D order, but between two different 3D orders. Since strong ferroelectricmagnetic coupling in HoMnO$_{3}$ is observed at the spin reorientation transition between these types of order, the fluctuations which give rise to this quasielastic scattering may give clues to the ferroelectricmagnetic coupling mechanism. [1] Sato et al., Phys. Rev. B 68, 104432 (2003). [Preview Abstract] 
Monday, March 15, 2010 1:51PM  2:03PM 
B36.00014: Phase Diagram and Magnetic Dynamics in Er$_{1x}$Y$_{x}$MnO$_{3}$ Tom Heitmann, Yuan Wang, Jagath C. Gunasekera, Owen P. Vajk We have grown singlecrystal samples of the hexagonal multiferroic Er$_{1x}$Y$_{x}$MnO$_{3}$ at different compositions. YMnO$_{3}$ orders in a P6'$_{3}$cm' phase, while ErMnO$_{3}$ orders in a P6'$_{3}$c'm phase. The boundary between these phases is of interest because of the strong coupling between ferroelectricity and magnetism observed at the spin reorientation transition between these phases in HoMnO$_{3}$. We find that Er$_{1x}$Y$_{x}$MnO$_{3}$ transitions completely from the P6'$_{3}$cm' to the P6'$_{3}$c'm phase over a very narrow composition range on the Yrich side of the phase diagram. We have also performed inelastic neutron scattering measurements on these samples, and find quasielastic scattering similar to that found in YMnO$_{3}$. However, as for Ho$_{1x}$Y$_{x}$MnO$_{3}$, this scattering exhibits outofplane correlations and is centered at locations other than the fundamental magnetic Bragg peak. [Preview Abstract] 
Monday, March 15, 2010 2:03PM  2:15PM 
B36.00015: Superexchange interaction revisited for orthorhombic perovskite manganites $R$MnO$_3$ ($R$=rare earth) Beom Hyun Kim, B. I. Min The manganese perovskite oxides $R$MnO$_3$ ( $R$= rareearth element) show the strong interplay between charge, orbital, lattice, and spin degrees of freedom. Depending on rareearth ions, their magnetic ground state varies from the $A$type to $E$type antiferromagnetism (AFM) through the spiral ordering and accordingly MnOMn bonding angles and local octahedral deformations are changed. Moreover, the ferroelectric properties emerge in the case of spiral or $E$type $R$MnO$_3$. In this study, we have studied the magnetic superexchange interaction in $R$MnO$_3$ based on the microscopic model incorporating the GdFeO$_3$type octahedral tilting and the JahnTeller (JT) distortion. We have found that (i) the account of $t_{2g}$ electrons is essential to describe both the nearestneighbor (NN) and nextnearestneighbor (NNN) superexchange interactions, (ii) the JT distortion angle as well as the octahedral tilting and the JT distortion strength is an important factor for the superexchange interactions, and (iii) two NNN interactions in the ab plane are anisotropic but are both antiferromagnetic. We have determined the magneticphase diagram of $R$MnO$_3$ and discussed the magnetic ground states in relation to the experiments. [Preview Abstract] 
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