Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session X47: Multiferroics and Magnetoelectricity in Complex OxidesFocus
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Sponsoring Units: GMAG DMP DCOMP Chair: Natalia Perkins, University of Minnesota Room: 710/712 |
Friday, March 6, 2020 11:15AM - 11:27AM |
X47.00001: THz spectroscopy of BiFeO3 in the magnetic-field-induced canted AFM state. Johan Viirok, Laur Peedu, Urmas Nagel, Toomas Room, Dávid Szaller, Vilmos Kocsis, Sandor Bordacs, Istvan Kezsmarki, Hans Engelkamp, Dima Kamensky, Komalavalli Thirunavukkuarasu, Mykhaylo Ozerov, Dmitry Smirnov, Jurek Krzystek, Yukihiro Ozaki, Toshimitsu Ito, Yasuhide Tomioka, Trinanjan Datta, Randy Fishman BiFeO3 is a well-known room temperature multiferroic material where the cycloidal magnetic order induces electric polarization in addition to existing polarization. The cycloidal order is transformed by strong magnetic fields into a canted antiferromagnetic (AFM) order above B=18T and the cycloidal modes are replaced by excitations of the canted AFM structure [U. Nagel et al., Phys. Rev. Lett., 110:257201, (2013)]. |
Friday, March 6, 2020 11:27AM - 11:39AM |
X47.00002: Magnetoelectric spectroscopy of spin excitations in LiCoPO4 Toomas Room, Johan Viirok, Laur Peedu, Urmas Nagel, Sandor Bordacs, Istvan Kezsmarki, Vilmos Kocsis, Yusuke Tokunaga, Yasujiro Taguchi, Yoshinori Tokura In this work [V. Kocsis et al., PRB100, 155124 (2019)] we study optical magnetoelectric (ME) effect using optical directional anisotropy as measured by the THz absorption spectroscopy of spin resonances in LiCoPO4. The antiferromagnetic domains are selected by ME poling and their population is measured by directional anisotropy [V. Kocsis et al.PRL121, 057601 (2018)]. Here we demonstrate that the directional anispotropy can also be used to investigate the form and the spectral dependence of the ME susceptibility tensor and hence to identify different spin-multipolar orders responsible for the ME effect. From the spectrum of the directional anisotropy one can determine the static ME coupling via the ME susceptibility sum rule. We conclude, for the poling magnetic field direction along the local electric polarization, the observed ME spin resonances are responsible for the static ME effect and the symmetric part of the ME tensor with zero diagonal elements dominates over the antisymmetric components. |
Friday, March 6, 2020 11:39AM - 11:51AM |
X47.00003: Model for the Spin Dynamics of the Multiferroic (NH4)2FeCl5 (H2O) Randy Fishman, Wei Tian, Jaime Fernandez-Baca, Janice L Musfeldt, Jun Hee Lee, Minseong Lee, John Singleton The multiferroic behavior of any material sensitively depends on the microscopic interactions between the spins. We evaluate the magnetic interactions in the multiferroic erythrodsiderite (NH4)2FeCl5 (H2O) by comparing inelastic neutron scattering spectra of a single crystal sample with a simple Heisenberg model containing five exchange interactions and an easy-plane anisotropy. The cycloidal spin state in every bc plane is produced by two competing exchange interactions. Using the observed wavevector of this cycloidal spin state is used as a constraint, excellent agreement is found between the observed and predicted spectra. The resulting exchange and anisotropy parameters are compared with the predictions of first-principle calculations. |
Friday, March 6, 2020 11:51AM - 12:03PM |
X47.00004: Tunable Magnetic and Ferroelectric Order Parameters in Sr1-xBaxMn1-yTiyO3 Omar Chmaissem, Kamal Chapagain, Bianca Haberl, Jeffrey Lynn, Saul Lapidus, Curtis Kenney-Benson, Bogdan M Dabrowski, Stephan Rosenkranz Multiferroic oxides have recently emerged as key materials with the potential to tackle the exploding demand for systems that enable efficient energy usage and enhance the functionality of spintronic devices. In this talk, I will discuss the recent development of single-site manganese-based multiferroic perovskite materials, Sr1-xBaxMn1-yTiyO3, with ferroelectric transition temperatures boosted to ~430 K. Using a series of temperature-dependent scattering experiments at various pressures, we demonstrate the tunable character of coupling between the magnetic and ferroelectric order parameters and show that ferroelectricity could be easily manipulated through the application of either external or chemical pressures. Measurements of the magnetic and structural properties under pressure allowed the construction of a detailed P-T phase diagram in which the diverse phases are delineated. Impressive spontaneous polarization values of ~30 μC/cm2, in agreement with Ti-free Sr1-xBaxMnO3, are calculated using an empirical c/a-based equation or derived from a point charge model with bond-lengths and angles determined by neutron diffraction. |
Friday, March 6, 2020 12:03PM - 12:15PM |
X47.00005: Insights into the coupled phenomena in molecular multiferroic (ND4)2[FeCl5(D2O)] via inelastic neutron scattering studies Wei Tian, Randy Fishman, Huibo Cao, Gabriele Sala, Daniel M. Pajerowski, Tao Hong, Luke L. Daemen, Yongqiang Cheng, Jaime A. Fernandez-Baca (ND4)2[FeCl5(D2O)] is a rare molecular magnet exhibiting direct coupling between magnetism and electric polarization as well as a very rich magnetic field versus temperature phase diagram[1-3]. In order to gain a deep understanding of the emergent coupled phenomena, we performed inelastic neutron scattering experiments to investigate the dynamics in this material. Our data analysis shows the spin dynamics can be described by a Heisenberg Hamiltonian model with an easy-plane anisotropy that captures the key observations. Our inelastic neutron scattering results also reveal the role the ion played in the intriguing properties observed in (NH4)2[FeCl5(H2O)]. |
Friday, March 6, 2020 12:15PM - 12:27PM |
X47.00006: Magnetization reversal by electric field in Co substituted bismuth ferrite thin film Masaki Azuma, Keisiuke Shimizu, Kei Shigematsu, Hajime Hojo Electric field manipulation of magnetization is intensively investigated because of potential application in low-power-consumption non-volatile magnetic memory devises. Ferroelectric BiFeO3 has a cycloidal space-modulated spin structure with a periodicity of 62 nm superimposed on the G-type antiferromagnetic structure. The presence of cycloidal ordering prohibits the appearance of net ferromagnetic magnetization due to spin canting and a linear magnetoelectric effect. We have observed a spin structure transition from low-temperature cycloidal one to high-temperature collinear one at ~200 K using Mössbauer spectroscopy in rhombohedral BiFe0.1Co0.9O3 thin films fabricated by PLD on SrTiO3 (STO) (111) substrate. Spontaneous magnetization of 0.03 uB/f.u. confined in a magnetic easy plane perpendicular to the electric polarization is generated by Dzyaloshinskii-Moriya interaction. Films fabricated on GdScO3 (110) substrate has out-of-plane component of magnetization which can be observed by MFM. It is demonstrated that the out-of-plane magnetization can be reversed by electric polarization reversal using PFM at room temperature. |
Friday, March 6, 2020 12:27PM - 1:03PM |
X47.00007: Spin-liquid-like state in ferroelectric TbInO3 with a nearly triangular lattice Invited Speaker: Valery Kiryukhin Quantum spin liquids (QSL) have been continuously attracting attention since Anderson’s seminal work in 1970’s. As most visionary ideas, QSLs have been found to be relevant to many diverse branches of physics, ranging from superconductivity to quantum computing applications. Known QSL candidate compounds are typically based on geometrically frustrated magnetic lattices, such as the kagome and triangular (TL) lattices. After decades of activity, their properties are still enigmatic, and the number of strong QSL candidates is limited. We describe a recently-discovered QSL candidate TbInO3, containing nearly-triangular layers of non-Kramers Tb3+ ions. No signs of static magnetic order are found down to the temperatures two orders of magnitude smaller than the effective interaction energy, by a variety of complementary techniques. Inelastic neutron scattering studies reveal a broad continuum of magnetic excitations located at the TL Brillouin zone boundary that can be described in the framework of the uncorrelated nearest-neighbor valence bonds model. TbInO3 is also ferroelectric, containing atomically-sharp domain boundaries that could host exotic states. These observations make TbInO3 a rather unique QSL candidate, in which fluctuating quantum magnetic state is combined with ferroelectricity. |
Friday, March 6, 2020 1:03PM - 1:15PM |
X47.00008: An annealing study of CaMn2O4-d, a possible multiferroic candidate Melissa Gooch, Hung-Cheng Wu, Liangzi Deng, Hung-Duen Yang, Paul C. W. Chu Manganese oxides have experienced a considerable increase in research interest due to their rich and complex phase diagrams. Ca-Mn-O is an excellent example, whose rich phase diagram contains phases that have been theoretically predicted to be multiferroic and CaMn2O4 to date is still not well understood and a hopeful candidate. Polycrystalline samples were synthesized and annealed with two different growth environments to further investigate the effect of oxygen deficiencies. Therefore, argon as well as oxygen gas flows were utilized. From initial dc magnetization and Cp measurements, the previously report TN ~ 220 K was observed for both samples. However, a spontaneous polarization (PS) was observed at ~ 253 K for the oxygen annealed sample with no applied field while no PS was observed up to 7 T and temperatures down to 2 K for the argon annealed sample. Anomalies above 260 K were detected in both samples, which were not only time-, but also field-dependent. Measurements are ongoing to gain greater insight into this complex system. |
Friday, March 6, 2020 1:15PM - 1:27PM |
X47.00009: Pressure effect on multiferroics investigation with neutron scattering Yan Wu, Wei Tian, Huibo Cao Multiferroics have attracted tremendous research interests with their rich physics and potential in constructing next-generation multifunctional devices. The type-II multiferroics have magnetic phase related ferroelectricity. In a system where the magnetic phase is closely correlated with crystal lattice, compressing the unit cell with high pressure would lead to distinct magnetic phase transitions and then tune the ferroelectricity. We studied systems mainly with neutron scattering techniques in identifying their magnetic phase transitions under pressures to provide understanding for change of the ferroelectric properties in the system. |
Friday, March 6, 2020 1:27PM - 1:39PM |
X47.00010: Magnetostructural domain wall patterning in ferrimagnetic spinels Lazar Kish, Adam Aczel, Lisa DeBeer-Schmitt, Alexander N. Thaler, Dalmau Reig-i-Plessis, Alexander Zakrzewski, Greg MacDougall
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Friday, March 6, 2020 1:39PM - 1:51PM |
X47.00011: Large and highly anisotropic magnetocaloric effects in disordered-perovskite RCr0.5Fe0.5O3 single crystals (R = Gd, Er) Hyunjun Shin, JongHyuk Kim, Donggun Oh, Young Jai Choi, Nara Lee We have successfully synthesized the disordered-perovskite RCr0.5Fe0.5O3 (R=Gd, Er) single crystals which crystallize in an orthorhombic Pbnm structure, and investigated anisotropic magnetic and magnetocaloric properties. In GdCr0.5Fe0.5O3, the isotropic nature of large Gd3+ moments leads to a tremendously large entropy change of ~50 J/kg K for both ab and c axes. On the other hand, ErCr0.5Fe0.5O3 exhibits a highly anisotropic magnetocaloric effect which results in a rotational entropy variation of ~21 J/kg K at the ordering temperature of Er3+ moments, TEr = 6 K. Our findings suggest the important roles of magnetic anisotropy of rare-earth magnetic ions and enrich fundamental and applied research on magnetic materials in view of distinct magnetic characteristics in disordered perovskites. |
Friday, March 6, 2020 1:51PM - 2:03PM |
X47.00012: An ab initio Study of Oxygen Vacancies in Ba2CuO4 and Sr2CuO4 Matthew Matzelle, Christopher Lane, Robert Markiewicz, Arun Bansil Oxygen vacancies play a key role in providing a fertile environment for superconductivity to emerge in the Ba2CuO4 and Sr2CuO4 family of novel superconductors. However, there is considerable debate as to whether or not the vacancies reside in the CuO2 plane or at the apical sites. Using state-of-the-art ab initio techniques, we systematically examine the energy landscape and electronic structure of oxygen vacancies in Ba2CuO4 and Sr2CuO4. A number of different configurations involving single and multiple vacancies are considered. Planar vacancies are found to yield lower energies, and materials with apical vacancies display exotic band structures. Finally, we will briefly connect our results to recent experiments. |
Friday, March 6, 2020 2:03PM - 2:15PM |
X47.00013: THz spectroscopy of spin excitations in magnetoelectric LiCoPO4 in high magnetic fields Laur Peedu, Toomas Room, Johan Viirok, Urmas Nagel, Sandor Bordacs, Vilmos Kocsis, Yusuke Tokunaga, Yasujiro Taguchi, Yoshinori Tokura, Hans Engelkamp, Uli Zeitler, Istvan Kezsmarki LiCoPO4 belongs to the family of magnetoelectric lithium-orthophosphates. In these compounds the cross-coupling between magnetization and electric polarization leads to variety of spin excitations that have entangled dynamic electric and magnetic properties. In this work THz spectroscopy was used to measure absorption spectra of spin excitations in LiCoPO4 single crystal below antiferromagnetic ordering temperature and in magnetic field up to 32 T. Three spin flop transitions for the magnetic field parallel to the magnetic easy axis were identified from the magnetic field dependence of spin excitations and from the magnetic field dependence of magnetization. Using polarized light and ME poling to create a single ME domain [V. Kocsis et al. PRL121, 057601 (2018), PRB100, 155124 (2019)], the selection rules of spin excitations were determined. Several magnetic-, electric-dipole active and magnetoelectric resonances were found. |
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