Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session F21: Focus Session: Multiferroics and Magnetoelectrics |
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Sponsoring Units: DMP Chair: Hans Christen, Oak Ridge National Laboratory Room: 323 |
Tuesday, March 19, 2013 8:00AM - 8:12AM |
F21.00001: Magnetoelectricity in Spinel FeCr$_{2}$S$_{4}$ Lin Lin, Dan Liu, Zhengyin Zhao, Jiajia Wen, Zhibo Yan, Shuai Dong, Junming Liu We report on ferroelectricity, magnetic susceptibility, dielectric property, and specific heat capacity of the polycrystalline spinel FeCr$_{2}$S$_{4}$. We provide clear evidence of a ferroelectric transition at $\sim$ 8.5K, which accompanies an orbital-ordering transition and a dielectric anomaly. The polarization increases with decreasing temperature, and reaches 3.6$\mu $C/m$^{\mathrm{2}}$ at 2 K. We also carry out detailed multiferroic measurements, and a remarkable magnetoelectric coupling is observed. A very small magnetic filed $H$ $\sim$ 500Oe enhances the polarization to 8.13.6$\mu $C/m$^{\mathrm{2}}$ at 2 K, with a magnetoelectric coupling coefficient $\alpha \sim$ 120{\%}. However, the polarization rapidly decreases for fields beyond $H \sim$ 1T. The multiferroic behavior of FeCr$_{2}$S$_{\mathrm{4}}$ is proposed to arise from competition between the spin-orbital coupling and the Jahn-Teller effect for the Fe ion.\\[4pt] [1] V. Fritsch, et al, Phys. Rev. Lett. \textbf{92}, 116401 (2004).\\[0pt] [2] R. Fichtl, et al, Phys. Rev. Lett. \textbf{94}, 027601 (2004).\\[0pt] [3] V. Tsurkan et al, Phys. Rev. B \textbf{81}, 184426 (2010). [Preview Abstract] |
Tuesday, March 19, 2013 8:12AM - 8:24AM |
F21.00002: The internal and external magnetoelectric effect in LiFeP$_{2}$O$_{7}$ K.-C. Liang, W. Zhang, B. Lorenz, Y.Y. Sun, P.S. Halasyamani, C.W. Chu We study the internal and external magnetoelectric (ME) effect of the single-crystalline LiFeP$_{2}$O$_{7}$ by magnetic, thermodynamic, and magnetoelectric measurements. The Fe$^{3+}$ spins form a canted antiferromagnetic (AFM) order below $T_{N}$ $\sim$ 27K with weak ferromagnetic components along the $b$-axis. A sharp peak found in the pyroelectric current at 27K indicates the strong internal ME interaction resulting in a sizeable polarization decrease. With external magnetic field applied, the ME polarization shows a combination of a linear and a quadratic field dependence below $T_{N}$, but it only shows the quadratic ME response above then. A large uniaxial magnetoelastic response in the thermal expansion data indicates strong spin-lattice coupling. A qualitative explanation regarding to the ME interaction between electric polarization and magnetic order parameters will be proposed and discussed. [Preview Abstract] |
Tuesday, March 19, 2013 8:24AM - 8:36AM |
F21.00003: Epitaxial Strain Induced Robust Multiferroicity in BiMnO$_{3}$ Xuezeng Lu, Xingao Gong, Hongjun Xiang By performing first principles calculations, we investigate the effects of the epitaxial strain on the properties of BiMnO$_{\mathrm{3}}$ films grown along the pseudocubic [001] direction. Unlike the ground state with the centrosymmetric $C$2/$c$ space group in bulk, two previously unreported phases, namely, paraelectric \textit{Pnma} and ferroelectric \textit{Cc} phases, are stabilized by epitaxial strain. Several surprising and interesting phenomena are revealed. In particular, we find a metal-insulator transition between the ferromagnetic metallic state and antiferromagnetic insulating ferroelectric state under compressive epitaxial strain. On the other hand, the tensile epitaxial strain stabilizes the ferromagnetic and ferroelectric \textit{Cc} state with the large polarization ($P$ \textgreater 80 $\mu $C/cm$^{2})$ and high Curie temperature (estimated $T_{c}$ $\sim$ 395 K). Moreover, there is a novel intrinsic magnetoelectric coupling in the multiferroic \textit{Cc} state with the easy magnetization axis tunable by the external electric field. [Preview Abstract] |
Tuesday, March 19, 2013 8:36AM - 9:12AM |
F21.00004: Chemistry and synthesis of new polar perovskites with small tolerance factors Invited Speaker: Alexei Belik ``Usual'' perovskite-type compounds with the general formula ABO3, where A is La-Lu and Y and B is V, Cr, Mn, Fe, Co, Ni, and Cu have been attracting a lot of attention for decades. ``Exotic'' perovskites are also highly interesting because new phenomena may emerge in them. The term ``exotic'' may include compounds with unusual oxidation states, unusual ion distribution, and unusual ions at the A site and B site. Perovskites with A $=$ Sc and In have small tolerance factors, and they can be prepared only at high pressure. We will discuss ``exotic'' perovskites with A $=$ Sc and In. A limited number of compounds can be prepared at 6 GPa. Results on (A1-yMy)MnO3 (A $=$ Sc and In, M $=$ Mn, Mg, Co, and Ni), InCrO3, ScCrO3, InRhO3, ScRhO3, InNi0.5Mn0.5O3, and ScNi0.5Mn0.5O3 will be presented. We will also describe a new class of multiferroic polar materials: In-based perovskites. We show that (In1-yMy)MO3 with y $=$ 0.112-0.176 and M $=$ Fe0.5Mn0.5 is isostructural with BiFeO3 (space group R3c) and has a high ferroelectric Curie temperature; (In1-yMy)MO3 is a canted antiferromagnet with the N\'eel temperature close to RT. Our results give a significant contribution to the development of RT multiferroics and also show new ways for the preparation of perovskite-type materials. [Preview Abstract] |
Tuesday, March 19, 2013 9:12AM - 9:24AM |
F21.00005: The search for new multiferroic ABF$_4$ fluorides via first-principles structure maps Brian Abbett, Aditi Krishnapriyan, Craig J. Fennie Transition metal ABF$_4$ fluorides are observed in a wide variety of different structure types. One, the BaMnF$_4$ structure, is an interesting family of polar (possibly ferroelectric) materials that display canted-antiferromagnetism, which has been predicted (Ederer and Spaldin) to reverse when the polarization reverses. This strong coupling between magnetism and polarization has motivated us to explore additional ABF$_4$ structure types. In this talk we will discuss our search for new multiferroic ABF$_4$ fluorides by creating structure maps from first principles. As a first step we categorize the ABF$_4$ compounds found in the ICSD. We focus on structures for which the B-site is octahedrally coordinated; these can be fitted into one of four categories: BaMF$_4$, Dion-Jacobson, and the so-called slip (100) or slip (110) structures. These four categories represent high symmetry structures which allow distortions to lower symmetry structures. Note that most of the known multiferroic ABF$_4$ compounds form in the BaMF$_4$ structure. We elucidate a simple descriptor that helps to build the chemical and physical intuition as to why a compound forms in this structure type needed for the rational design of new multiferroic ABF$_4$ fluorides. [Preview Abstract] |
Tuesday, March 19, 2013 9:24AM - 9:36AM |
F21.00006: Magnetic field enhanced structural instability in EuTiO$_{3}$ Zurab Guguchia, Hugo Keller, J\"{u}rgen K\"{o}hler, Annette Bussmann-Holder EuTiO$_{3}$ undergoes a structural phase transition from cubic to tetragonal at $T_{\rm S}$ = 282 K which is not accompanied by any long range magnetic order. However, it is related to the oxygen ocathedra rotation driven by a zone boundary acoustic mode softening. Here we show that this displacive second order structural phase transition can be shifted to higher temperatures by the application of an external magnetic field (${\Delta}$$T_{\rm S}$ ${\simeq}$ 4 K for $\mu_{0}$$H$ = 9 T). This observed field dependence is in agreement with theoretical predictions based on a coupled spin-anharmonic-phonon interaction model. [Preview Abstract] |
Tuesday, March 19, 2013 9:36AM - 9:48AM |
F21.00007: Spin-Lattice Coupling and Third Neighbor Magnetic Interactions in EuTiO$_3$ Turan Birol, Craig J. Fennie An ongoing challenge in materials physics is to identify materials that display a strong coupling between the electrical polarization and magnetism. EuTiO$_3$ is one such material that has been of much recent interest. This novel material is antiferromagnetic and paraelectric in bulk but becomes simultaneously ferromagnetic and ferroelectric under biaxial strain due to a rather large spin-lattice (phonon) coupling. In this talk we will present the results of our first-principles study on the effect of ferroelectric distortions and octahedral rotations on the magnetic exchange interactions in EuTiO$_3$. We elucidate the evolution of the octahedral rotation pattern with strain and show how they influence the properties of the multiferroic phase. Going beyond the proposed cation-mediated exchange for EuTiO$_3$, which has been linked to the large spin-lattice coupling in this material, we uncover the importance of third-neighbor magnetic interactions and illustrate how it is responsible for the ``giant'' cross-field magnetoelectric effect recently demonstrated. [Preview Abstract] |
Tuesday, March 19, 2013 9:48AM - 10:00AM |
F21.00008: Magneto-orbital helices: a novel coupling mechanism between magnetism and ferroelectricity in multiferroic CaMn$_7$O$_{12}$ Paolo G. Radaelli, Natasha Perks, Roger D. Johnson, Christine Martin, Laurent Chapon The trigonal quadruple perovskite CaMn$_7$O$_{12}$ displays one of the largest magnetically induced ferroelectric polarisations measured to date (2870 $\mu$C m$^{-2}$). Ferroelectricity appears below 90 K, together with an incommensurate helical magnetic modulation, and cannot be explained within the framework developed for cycloidal magnets [2]. We report an unprecedented magneto-orbital texture in multiferroic CaMn$_7$O$_{12}$, which is directly connected to ferroelectricity[3]. X-ray and neutron diffraction characterisation of the structural and magnetic modulations in these ``magneto-orbital helices'', and analysis of magnetic exchange shows that orbital order is crucial in stabilising a chiral magnetic structure. Additionally, the presence of a global structural rotation enables the magnetic helicity to couple with the lattice, giving rise to electric polarisation. These novel principles open up the possibility of discovering new multiferroics with even larger polarization and higher transition temperatures. [1] G. Zhang, \textit{et al.}, Phys. Rev. B 84 (2011) 174413. R.D. Johnson \textit{et al.}, Phys. Rev. Lett. 108, 067201 (2012). [2] M. Mostovoy, Phys. Rev. Lett. 96, 067601 (2006). [3] N. Perks \textit{et al.}, Nat. Comm., \textit{in press}. [Preview Abstract] |
Tuesday, March 19, 2013 10:00AM - 10:12AM |
F21.00009: Magneto-Electric Coupling in Single Crystal Cu$_2$OSeO$_3$ Studied by a Novel Electron Spin Resonance Technique Alexander Maisuradze, Alexander Shengelaya, Helmuth Berger, Dejan Djoki\'c, Hugo Keller The magneto-electric (ME) coupling on spin-wave resonances in single-crystal Cu$_2$OSeO$_3$ was studied by a novel technique using electron spin resonance combined with electric field modulation. An external electric field ${\bf E}$ induces a magnetic field component $\mu_0 H^i = \gamma E$ along the applied magnetic field ${\bf H}$ with $\gamma=0.7(1)~ \mu$T/(V/mm) at 10 K. The ME coupling strength $\gamma$ is found to be temperature dependent and highly anisotropic. $\gamma(T)$ nearly follows that of the spin susceptibility $J^M(T)$ and rapidly decreases above the Curie temperature $T_{\rm c}$. The ratio $\gamma/J^M$ monotonically decreases with increasing temperature without an anomaly at $T_{\rm c}$. [Preview Abstract] |
Tuesday, March 19, 2013 10:12AM - 10:24AM |
F21.00010: Strong Dzyaloshinskii-Moriya Interaction and Origin of Ferroelectricity in Cu$_{2}$OSeO$_{3}$ Ji-Hui Yang, Zheng-Lu Li, Xuezeng Lu, X.G. Gong, Hongjun Xiang, M.-H. Whangbo, Su-Huai Wei In this work, we try to understand the skyrmions recently observed experimentally in Cu2OSeO3 system, as well as its origin of ferroelectricity. Based on the spin Hamiltonian, we developed four-state-energy-mapping method to derive these spin interaction parameters. For this system, we found a very large ratio between the DM term and the symmetric exchange interaction. Besides, the spin arrangements in the ground state are found degenerate and the spin energy is independent of the propagation vector q. Taking these two factors into account, we explained the experimental observation of skyrmions to some extent. Then we built a model to describe the polarization of this system. By the symmetry analysis, the ferroelectricity is supposed to result from the spin single-site term, as is confirmed by direct calculations of our model. Using this model, we analyzed its ferroelectricity dependence of the spin arrangement and find the largest polarization happens when the spins are along \textless 111\textgreater\ direction, in excellent agreement with the experimental results. [Preview Abstract] |
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