Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session B21: Focus Session: Hexagonal Ferrites and Manganites |
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Sponsoring Units: DMP Chair: Nicole Benedek, University of Texas at Austin Room: 323 |
Monday, March 18, 2013 11:15AM - 11:27AM |
B21.00001: Multiferroic vortices Sang-Wook Cheong, Seung Chul Chae, Xueyun Wang, Fei-Ting Huang, Yoichi Horibe Hexagonal REMnO$_3$ (RE=Ho, Er, Tm, Yb, Lu) is an improper ferroelectric where the size mismatch between RE layers and Mn-O layers induces a simultaneous ferroelectric-trimerization structural phase transition [1]. The six types of ferroelectric-trimerization domains merge one point, and form a vortex or antivortices, depending on vorticity. A zoo of vortices and antivortices form into a topologically-nontrivial network, and intriguing collective magnetism develops at the domain walls of the vortex-antivortex network. In addition, we found that bound states of vortices and antivortices can also develop. We will discuss the formation of the vortex-antivortex network and the vortex-antivortex bound states in terms of the interaction between two neighboring domain walls and that between a vortex and an antivortex.\\[4pt] [1] T. Choi et al., Nature Mater. \textbf{9}, 253 (2010).\\[0pt] [2] S. C. Chae et al., PRL \textbf{108}, 167603 (2012). [Preview Abstract] |
Monday, March 18, 2013 11:27AM - 11:39AM |
B21.00002: Unfolding Vortices to Topological stripes in a multiferroic Xueyun Wang, Myung-Geun Han, Yoichi Horibe, Toshihiro Aoki, Yimei Zhu, Sang-Wook Cheong Hexagonal REMnO$_{\mathrm{3}}$ (RE$=$Ho, Er, Tm, Yb, Lu) is an improper ferroelectric where the size mismatch between RE layers and Mn-O layers induces a simultaneous ferroelectric-trimerization structural phase transition [1]. Two distinct domain configurations have been observed in REMnO$_{\mathrm{3}}$ (RE$=$rare earths): vortex domains vs. stripe domains [2]. However, the rapport between those topologically distinct domain patterns has never been studied. We have investigated the transformation process between vortex domains and stripe domains with the variation of temperature and the application of various strains on thin-plate-like crystals. [1] T. Choi \textit{et al.}, Nature Mater. 9, 253 (2010). [2] S. C. Chae \textit{et al}., PRL 108, 167603 (2012). [Preview Abstract] |
Monday, March 18, 2013 11:39AM - 11:51AM |
B21.00003: Ferroelectric domain formation and reversal by cation substitution in magnetoelectric gallium ferrite epitaxial thin films R. H. Shin, S. H. Oh, W. Jo, C. Lefevre, F. Roulland, A. Thomasson, C. Meny, N. Viart Linear magnetoelectric Ga$_{\mathrm{2-x}}$Fe$_{\mathrm{x}}$O$_{\mathrm{3}}$ (GFO) is ferrimagnet at room temperature (RT) (T$_{\mathrm{C}}=$370 K at x$=$1.4) from Fe spin of d orbitals in octahedral Fe1(opposite direction), Fe2, and Ga2 sites along c-axis. According space group as Pc2$_{\mathrm{1}}$n, ferroelectric ordering should be here along b-axis but have not observed, experimentally. Several scenarios of ferroelectricity in GFO have been suggested such as displacement of Fe ions, structural change, and so on. In the scenarios, it is very difficult to obtain their polarization because of tiny quantity and high domain wall (DW) formation energy. In this talk, we suggest the cation substituted GFO can be promising RT multiferroic showing ferroelectric ordering. We tried two kinds of direction: 1. Obtain polarization reversal under high magnetic and electric field to overcome high DW formation energy. 2. Apply chemical strain to make DW formation energy low. Though, when we applied chemical strain by substituting divalent cations, leakage current that overshadow polarization reversal was strongly reduced, ferromagnetic ordering was lost at RT owing to magnetic dilution by nonmagnetic cation like Mg$^{\mathrm{2+}}$. Therefore, we discuss how to obtain ferroelectric polarization in the GFO thin films conserving RT ferrimagnet. [Preview Abstract] |
Monday, March 18, 2013 11:51AM - 12:27PM |
B21.00004: Strong coupling of ferroelectricity and magnetism in the hexagonal ferrites Invited Speaker: Hena Das During the last decade one of the most extensively studied class of multiferroics has been the hexagonal rare-earth manganites RMnO$_3$ where R=Dy-Lu, Y, Sc. These compounds exhibit antiferromagnetic (AFM) order with a N\'eel temperature $\rm T_N\approx 100 K$. In addition, they are improper ferroelectrics ($\rm T_C > 1200K$) driven a by zone-tripling structural distortion associated with a buckling of the R-planes and a rotation of the oxygen trigonal bipyramids. The improper nature of the transition is responsible for the fascinating, topologically protected trimer-domains. Even though magnetism and ferroelectricity in these materials are not intrinsically coupled, there is a non-trivial interaction between the structural and magnetic domain walls. In contrast to the manganites, the ground state structure of the rare-earth ferrites RFeO$_3$ is the orthorhombic perovskite. Recently, however, thin films of RFeO$_3$ have been epitaxially stabilized in the hexagonal rare-earth manganite structure. This development has triggered several new studies of these hexagonal ferrite systems. Similar to manganites, ferrites exhibit ferroelectricity above room temperature and crystallize in P6$_3$cm polar structure but conflicting results have been reported as to the origin of ferroelectricity in these materials. Unlike the manganites, recent neutron diffraction measurements suggest a considerably high AFM ordering temperature, $T_N=$440 K. Additionally there is an indication of a second temperature, $ T_{\rm wFM}\sim100K$, at which weak ferromagnetism has been observed. In this work my collaborators (Alex Wysocki and Craig J. Fennie) and I address the nature of ferroelectricity and magnetic order in the RFeO$_3$ systems from first-principles. We elucidate the origin of ferroelectricity in the rare-earth ferrites and provide many useful insights into their magnetic behavior, which we will show is fundamentally different than that observed in the manganites. Combining first-principles calculations with a detailed modeling of the magnetic structure we will also show how this difference leads to an interplay between ferroelectricity and magnetism in the ferrites. This strong coupling, absent in the hexagonal manganites, manifests itself in a nontrivial way that may be useful for voltage controlled magnetic functionalities. [Preview Abstract] |
Monday, March 18, 2013 12:27PM - 12:39PM |
B21.00005: Is hexagonal InMnO$_3$ ferroelectric? Fei-Ting Huang, Yoichi Horibe, Xueyun Wang, Sang-Wook Cheong, Shigeo Mori Hexagonal manganite (h-REMnO$_3$; RE=rare earths) shows a unique improper ferroelectricity, accompanying a structural trimerization. RE can be replaced by In, which is much smaller than any RE ions. Recently, Oak {\it{et al.}} [1] suggested InMnO$_3$ is ferroelectric from the results of first-principles calculations, while Kumagai {\it{et al.}} [2] proposed a non-ferroelectric ground state. In this talk, we will report the results of our investigation on the structural domains and local structural distortions of InMnO$_3$ using dark-field transmission electron microscopy. We demonstrate that InMnO$_3$ shows a distinct $\sqrt{3}\times\sqrt{3}$-type superstructure from the high-temperature paraelectric phase (P6$_3$/mmc), and the domain structure can be delicately controlled by varying the synthesis and annealing conditions. The correlation between physical properties and local structural distortions in the InMnO$_3$ will be discussed in detail. [1] M.-A. Oak, J.-H. Lee, H. M. Jang, J. S. Goh, H. J. Choi and J. F. Scott, PRL \textbf{106}, 047601 (2011). [2] Y. Kumagai, A. A. Belik, M. Lilienblum, N. Leo, M. Fiebig, and N. A. Spaldin, PRB \textbf{85}, 174422 (2012). [Preview Abstract] |
Monday, March 18, 2013 12:39PM - 12:51PM |
B21.00006: Far- and mid-infrared emission and reflection of magnetoelectric RMnO$_3$ and RCrO$_3$ (R$=$Rare Earth) Nestor E. Massa, Leire del Campo, Domingos De Sousa Meneses, Patrick Echegut, Maria Jesus Martinez-Lope, Jose Antonio Alonso Far- and mid-infrared emission and reflection spectra of ferrielectric hexagonal TmMnO$_{3}$ show that small polarons, a paramagnetic collective electronic mode, and lower than T$_{\mathrm{N}}$ soft hybrid modes are in concomitant relation. CO$_{\mathrm{2}}$ laser heating in dry air triggers oxidation and Mn$^{3+}$- Mn$^{4+}$ double exchange hopping conductivity. A collective excitation in the paramagnetic phase is assigned to e$_{\mathrm{g}}$ electrons in THz low energy d-orbital fluctuations. It locks-in at the E-type antiferromagnetic onset (T$_{\mathrm{N}}$ $\sim$ 80K) into soft bands that harden simultaneously down to 4 K with temperature dependence given by the magnetic long range order coupling of the collective electric dipole. They have T$_{\mathrm{N}}$ as critical temperature and critical exponents suggesting a second order phase transition. They also match zone center spin wave modes measured in isomorphous LuMnO$_{3}$ (Lewtas et al, Phys. Rev. B~\textbf{82}, 184420 (2010)). Both excitations, magnons y electric dipoles, are generated by electrons e$_{\mathrm{g}}$ in deformed d-orbitals. Sharing this behavior with orthorhombic NdMnO$_{3}$ there is no evidence of new phonons in a structural deformation down to 4K Preliminary results in ErCrO$_{3}$ (T$_{\mathrm{N}}$ $\sim$ 130 K) show the emerging soft bands in an order-disorder scenario. Overall, we conclude that magnetoelastic deformations in an orbital fluctuating environment are close related to magnetoelectric couplings. [Preview Abstract] |
Monday, March 18, 2013 12:51PM - 1:03PM |
B21.00007: Synthesis, Structural Characterization and Magnetic Properties of YbFe$_{\mathrm{1-x}}$Mn$_{\mathrm{x}}$O$_3$ (0.0 $\le$ x $\le$ 1.0) Perovskites C. Hernandez, E. Chavira, I. Rosales, A. Tejada, L. Huerta, E.E. Marinero We report on the synthesis, structural characterization and magnetic properties of YbFe$_{\mathrm{1-x}}$Mn$_{\mathrm{x}}$O$_3$ (0.0$ \le $ x $\le$ 1.0) perovskites. Compounds with x$=$\textbf{ 0, 0.2, 0.4, 0.6, 0.8 and 1.0} were synthesized by solid state reaction. We find that the perovskites with x$=$0, 0.2 exhibit an orthorombic crystalline structure, whereas those with x$=$0.6, and 1.0 are hexagonal. A mixture of both hexagonal and orthorhombic phases are observed for x$=$ 0.4 and 0.8. The magnetic properties of these materials have been studied as a function of temperature (2K -- 300K). In the low temperature regime (2K -- 30K), we observe previously unreported magnetic transitions whose transition temperature depends on the amount of Mn incorporated in the perovskite. We will describe the possible origin of these magnetic transitions in terms of the structural properties of the materials studied. [Preview Abstract] |
Monday, March 18, 2013 1:03PM - 1:15PM |
B21.00008: Crystal Structure, Electric Polarization and Heat Capacity Measurements on Small R-Ion Multiferroic Hexagonal RMnO$_{3}$ Tian Yu, Peng Gao, Tao Wu, Trevor Tyson, Roger Lalancette Crystal structure, electric polarization and heat capacity measurements on the hexagonal multiferroic RMnO$_{3}$ reveal that small R ion (Lu and lower cation size) systems are ferroelectric and possess the same space-group as YMnO$_{3}$. Combined local and long range structural measurements were conducted by XAFS, PDF and single crystal and powder XRD methods. The influence of the Mn-O and R-O distribution on the electric polarization is discussed. Point charge estimates of the electrical polarization are given for comparison with the YMnO$_{3}$ system. This work is supported by DOE Grant DE-FG02-07ER46402. [Preview Abstract] |
Monday, March 18, 2013 1:15PM - 1:27PM |
B21.00009: Temperature Dependent Properties of Perovskite Small R-Ion RMnO$_{3}$ Systems Haiyan Chen, Tian Yu, Peng Gao, Trevor Tyson, Keun Hyuk Ahn Perovskite small ion E-type systems with radii smaller than that of Lu have been synthesized. The structure, heat capacity and magnetic measurements have been used to compare them with standard E-type systems such as LuMnO$_{3}$ and HoMnO$_{3}$. Analysis of the structure is combined with theoretical estimates to relate the electronically driven polarization with the atomic structure. [Preview Abstract] |
Monday, March 18, 2013 1:27PM - 1:39PM |
B21.00010: Critical Structural Parameters Influencing Magnetic Transition Temperatures in Multiferroic Hexagonal RMnO$_{3}$ Trevor Tyson, Tian Yu, Tao Wu, Catherine Dubourdieu, Sang-wook Cheong Multiferroic hexagonal RMnO$_{3}$ systems with a broad range of transition temperatures and including some with spin rotation transitions have been studied. Detailed temperature depended structural measurements have been conducted to extract the static and dynamic changes. The structural measurements are combined with qualitative theoretical arguments to determine the critical parameters which influence the magnitude of the magnetic ordering temperature. Suggestion are made on ways to optimize it to enable higher temperature multiferroic behavior. [Preview Abstract] |
Monday, March 18, 2013 1:39PM - 1:51PM |
B21.00011: Insights on Electric Polarization in $E$-type $R$MnO$_{3}$ Tao Wu, Trevor A. Tyson, Haiyan Chen, Zhiqiang Chen, Ryan Tappero, Keun H. Ahn, Sungbaek Kim, Sang-Wook Cheong Orthorhombic perovskite $E$-type $R$MnO$_{3}$ multiferroic systems were prepared by high pressure synthesis and solid state reaction. High pressure synchrotron x-ray diffraction and x-ray absorption spectroscopy measurements were performed to explore the structural changes. The influence of the pressure on the electrical polarization is discussed. Theoretical analysis is used to predict pressure dependence of the polarization from the structural data derived from the refinements. This work is supported by DOE Grant DE-FG02-07ER46402. [Preview Abstract] |
Monday, March 18, 2013 1:51PM - 2:03PM |
B21.00012: Ferroelectric and ferromagnetic properties of Ga$_{\mathrm{x}}$ CoFe$_{\mathrm{2-x}}$O$_{4}$ /BaTiO$_{3}$ Yan Ni, Cajetan Nlebedim, David Jiles Single phase magnetoelectric materials are limited in application. Consequently, practical application of magnetoelectric materials requires the development of composite materials in which piezoelectric and magnetostrictive phases are coupled via interfacial strain. In addition to strong coupling, it is desirable that both the magnetostrictive and piezoelectric phases possess high sensitivity, d$\lambda $/dH and dP/d$\sigma $ respectively. Of all the substituted cobalt ferrite studies, CoGaxFe2-xO4 has been shown to have the highest strain sensitivity. In the present study, CoGaxFe2-xO4 (x$=$0.1, 0.2, 0.3) has been combined with BaTiO3 to fabricate a y(CoGaxFe2-xO4)-(1-y)BaTiO3 (y $=$ 0.4, 0.5 and 0.6) magnetoelectric composite samples. Crystal structure, microstructure and compositions of the samples were verified by XRD, SEM and EDX. The effect of the BaTiO3 phase on the magnetostrictive properties of CoGaxFe2-xO4 and the effect of the CoGaxFe2-xO4 phase on the piezoelectric properties of BaTiO3 will be presented with respect to the magnetoelectric properties of the composites. [Preview Abstract] |
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