Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session C02: Dielectric & Ferroic Oxides -- Magnetoelectric EffectsFocus
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Sponsoring Units: DMP DCOMP GMAG Chair: John Heron, University of Michigan Room: BCEC 107A |
Monday, March 4, 2019 2:30PM - 3:06PM |
C02.00001: Multiferroics: hidden functionalities beyond magnetoelectric coupling Invited Speaker: Manfred Fiebig Requirements to "good multiferroics" are tough. They are supposed to have a spontaneous magnetization and polarization, preferably parallel to each other, with a strong magnetoelectric coupling between them. Inevitably, this leads to a multiferroic state that is described by a very complex set of order parameters – complex enough to provide the symmetry degrees of freedom to fulfil so many requirements at once [1]. With the focus on electric-field-controlled magnetic order, it goes unnoticed that these degrees of freedom will permit many functionalities other than a refined magnetoelectric coupling. In my talk, I will describe the quest for such functionalities in our group. I will discuss up to four cases. (i) For the multiferroic hexagonal manganites I will show that amplitude and phase of the order parameter may exhibit different coherence length. Taking this into account, we resolve the long-standing controversial question of how exactly the topological ferroelectric state in this system arises [2]. (ii) The emergence of a magnetic bulk phase transition out of the spin structure in the domain walls is shown for (Tb,Dy)FeO3. (iii) Inversion of a ferroelectric and a ferromagnetic multi-domain state in homogeneous external fields is demonstrated: In each domain, the direction of the order parameter is reversed but the domain pattern as such is left untouched [3]. |
Monday, March 4, 2019 3:06PM - 3:18PM |
C02.00002: Theory of orbital magnetic quadrupole moment and magnetoelectric susceptibility Atsuo Shitade, Hikaru Watanabe, Youichi Yanase We derive a quantum-mechanical formula of the orbital magnetic quadrupole moment (MQM) in periodic systems by using the gauge-covariant gradient expansion. This formula is valid for insulators and metals at zero and nonzero temperature. We also prove a direct relation between the MQM and magnetoelectric (ME) susceptibility for insulators at zero temperature. It indicates that the MQM is a microscopic origin of the ME effect. Using the formula, we quantitatively estimate these quantities for room-temperature antiferromagnetic semiconductors BaMn2As2 and CeMn2Ge2−xSix . We find that the orbital contribution to the ME susceptibility is comparable with or even dominant over the spin contribution. |
Monday, March 4, 2019 3:18PM - 3:30PM |
C02.00003: Inelastic Neutron Scattering measurements on phonon-magnon coupling in BiFeO3 Guangyong Xu, Zhijun Xu, John A. Schneeloch, Jinsheng Wen, Masaaki Matsuda, Barry L. Winn, Daniel Pajerowski, Yang Zhao, Chris Stock, Peter M Gehring, T. ushiyama, Y. Yanagisawa, Y. Tomioka, Toshimitsu Ito, Robert J Birgeneau We use inelastic neutron scattering to study phonons in multiferroic BiFeO3. When the low energy optic phonon is probed, an intensity enhancement is observed when the system enters the antiferromagnetic phase at TN=640K. It is interpreted as a possble dynamic coupling between phonons and magnons through the DM interaction. Polarized neutron measurements are performed to confirm the lattice nature of this enhancement, in other words, to show that this is more a "magneto-phonon" mode rather than a "electro-magnon" mode. We will also discuss neutron scattering measurements on higher energy phonons that could also be affected by the proposed dynamic coupling. |
Monday, March 4, 2019 3:30PM - 3:42PM |
C02.00004: RIXS excitations of polar magnet Fe2Mo3O8 Hsiao-Yu Huang, Amol Singh, Abhishek Nag, Kejin Zhou, Andrew Walters, Mirian Garcia-Fernandez, Jun Okamoto, Ashish Chainani, Yu-Miin Sheu, Takashi Kurumaji, Yoshinori Tokura, Chien-Te Chen, Di-Jing Huang Cross control of magnetization (electric polarization) by an external electric (magnetic) field, i.e. magnetoelectric (ME) effect, is a key in designing novel multiferroic devices. The polar magnet Fe2Mo3O8 has been demonstrated to be a promising multiferroic material recently. The ME coupling is not only strong but also compositionally tunable. Upon Zn doping higher than 12.5 %, the antiferromagnetic ground state becomes ferrimagnetic state accompanying a change in ME coefficient. To study the electronic structure of (Fe1-xZnx)2Mo3O8, we carried out comprehensive measurements including Hard X-ray photoemission, soft x-ray absorption and resonant inelastic X-ray scattering. Our results disentangle the electronic properties of octahedral and tetrahedral Fe2+and provide spectroscopic evidence that the doped Zn favors to replace tetrahedral Fe in the doped compound. We observed peculair temperature and polarization dependences of low-energy RIXS excitations across the phase transition of Fe2Mo3O8. |
Monday, March 4, 2019 3:42PM - 3:54PM |
C02.00005: Local magneto-electric response of Cr2O3 investigated with spin polarized positive muons Martin Dehn, Donald J Arseneau, Sarah R Dunsiger, Bassam Hitti, Stefan Holenstein, Michael Fechner, Hubertus Luetkens, W Andrew MacFarlane, Ryan M. L. McFadden, Quintin N Meier, Gerald D Morris, Zaher Salman, Nicola Spaldin, Robert F Kiefl The bulk properties of the prototypical linear magneto-electric antiferromagnet Cr2O3 have been extensively studied. Here, we report on a muon spin rotation (μSR) study using spin polarized muons to probe the local magneto-electric response in order to investigate magnetoelectricity on a microscopic level. We find that the muon, a light interstitial probe, occupies several distinct stopping sites in Cr2O3, and displays a rich dynamic behavior that we interpret in the context of local muon hopping and thermally activated site transitions. Furthermore, when Cr2O3 is prepared in a single magnetic domain, a shift in the local magnetic field is observed in response to an applied electric field, with the sign of the shift depending both on the field direction and domain state. The origin of this apparent magneto-electric effect is discussed. |
Monday, March 4, 2019 3:54PM - 4:06PM |
C02.00006: Magnetoelectric Effect in Type II Multiferroic HoFeWO6 Moein Adnani Takantapeh, Hung-Cheng Wu, Narayan Poudel, Melissa Gooch, Liangzi Deng, Zheng Wu, Paul C. W. Chu In type II multiferroics, the ferroelectricity originates from the magnetic ordering as it breaks the inversion symmetry. In this work, we investigated multiferroicity in HoFeWO6 which belongs to the RFeWO6 (R=Rare-earth) system recently suggested to be type II multiferroic [1]. We found that this compound orders antiferromagnetically below TN ~17 K. Observation of an anomaly in dielectric constant and dielectric loss, as well as a polarization switchable by an electric field at the same temperature, reveal the ferroelectric nature of this transition. |
Monday, March 4, 2019 4:06PM - 4:18PM |
C02.00007: Electric-field control of magnetization, Jahn-Teller distortion and orbital ordering in ferroelectric ferromagnets Lan Chen, Changsong Xu, Hao Tian, Hongjun Xiang, Jorge Iñiguez, Yurong Yang, Laurent Bellaiche Controlling the direction of the magnetization by an electric field in multiferroics that are both ferroelectric and strong ferromagnetic will open the doors to the design of next generation of spintronics and memory devices. Unfortunately, this has never been achieved so far mostly because these materials are very scarce and/or may not have a large enough magnetoelectric coupling. Here, using first-principles simulations, we report the discovery that PbTiO3/LaTiO3 (PTO/LTO) superlattice does possess such highly-desired control, as evidenced by the electric-field-induced rotation of 90° and even full possible reversal of its magnetization in some cases. Moreover, such "wunderbar'' systems also exhibit Jahn-Teller distortions, as well as orbital orderings, that are switchable by electric field, therefore making PTO/LTO of importance for the tuning of electronic properties too. Other possible materials possessing such couplings are also discussed, which further renders the presently reported electric controls to be a new general strategy to tune various properties of functional materials. |
Monday, March 4, 2019 4:18PM - 4:30PM |
C02.00008: Multiferroic Behavior in Fe doped BaTiO3 single crystals Peter Finkel, Margo Staruch, Hatem ElBidweihy, Markys Cain, Paul Thompson Single crystals of BaTiO3 (BTO) that have been doped at the titanium site with Fe3+ or Mn3+ have previously been shown to demonstrate large and recoverable electrostrains of up to 0.8 % that is thought to be due to the alignment of defects (i.e. O2- vacancies) with the crystallographic symmetry in the ferroelectric state when the samples are aged.[1,2] There is also the possibility that the incorporation of a magnetic ion could give rise to a magnetic signature and even potentially multiferroic coupling in these doped samples, the possibility of which has not been previously investigated. This would be of great interest as a new path to single phase multiferroic materials. In this presentation, results from magnetic and ferroelectric measurements will be presented for a 0.5% Fe doped BTO crystal. Anomalies in the magnetization at the ferroelectric-ferroelectric phase transitions, magnetocapacitance effects, and changes in the polarization with applied magnetic field confirm the existence of magnetoelectric coupling. The potential origins of this phenomenon will be discussed. |
Monday, March 4, 2019 4:30PM - 4:42PM |
C02.00009: Magnetodielectric effect in ErFeO3 single crystals Dong Gun Oh, Hwan Young Choi, Young Jai Choi, Nara Lee We investigated magnetodielectric effect of orthoferrite single crystals of ErFeO3, synthesized by the flux method using PbO flux. The canted antiferromagnetic order of Fe3+ moments arises below TN ≈ 640 K and a spin reorientation transition occurs at TSR ≈ 93 K, which accompanies the rotation of weak net magnetic moments from the c- to a-axis. As the temperature is further decreased, a long-range magnetic order of Er3+ spins emerges at TEr ≈ 4 K. From our investigation of anisotropic dielectric constant meausurements, the magnetodieletric effect, described as the variation in the dielectric constant by applying external magnetic fields, is found in a broad range of temperature. Especially, the temperature dependence of dielectric constant exhibits a sharp anomaly at TEr, as similarly observed in magnetic susceptibility along the c axis. In addition, a nonlinear variation in the isothermal dielectric constant, with a similar hysteretic behavior of the magnetic-field derivative of magnetization, is observed. The simultaneous non-linear variations of isothermal magnetization and dielectric constant below TEr suggest the important role of magnetic rare earth ions in magnetoelectric characteristics of the orthoferrite compound. |
Monday, March 4, 2019 4:42PM - 4:54PM |
C02.00010: Magnetoelectric properties in antiferromagnets composed of square cupolas A(TiO)Cu4(PO4)4 (A = Ba, Sr, Pb) Yasuyuki Kato, Yukitoshi Motome We study the magnetoelectric properties in a newly synthesized series of quasi-two-dimensional magnets A(TiO)Cu4(PO4)4 (A = Ba, Sr, Pb), by the cluster mean-field theory for a minimal quantum spin model [1,2]. The important building block of these compounds is Cu4O12 forming antiferromagnetic square cupolas where the local inversion symmetry is absent, and the Dzyaloshinskii-Moriya interaction is activated. By this antisymmetric interaction, the so-called quadrupole type spin configuration is stabilized at zero magnetic field. For nonzero magnetic fields, the magnetization curves are experimentally obtained up to above the saturation field for all A, and several anomalies are observed depending on the magnetic field directions. Our analysis well reproduces the full magnetization curves by tuning model parameters. Elaborating the phase diagram of the model, we show that the anomalies are explained by magnetoelectric phase transitions. Our theory also accounts for the dielectric anomaly observed in experiments. Furthermore, we show that the magnetoelectric behavior is well explained by the cluster multipole decomposition of complex spin configurations stabilized under the magnetic field. |
Monday, March 4, 2019 4:54PM - 5:06PM |
C02.00011: Realizing Magnetoelectric Coupling with Hydroxide as a Knob JinYang Ni Materials with a coexistence of magnetic and ferroelectric order (i.e., multiferroics) provide an efficient route for the control of magnetism by electric fields. Unfortunately, a long-sought room temperature multiferroic with strongly coupled ferroelectric and ferromagnetic (or ferrimagnetic) orderings is still lacking. Here, we propose that hydrogen intercalation in antiferromagnetic transition metal oxides is a promising way to realize multiferroics with strong magnetoelectric coupling. Taking brownmillerite SrCoO2.5 as an example, we show that hydrogen intercalated SrCoO2.5 displays strong ferrimagnetism and large electric polarization in which the hydroxide acts as a new knob to simultaneously control the magnetization and polarization at room temperature. We expect that ion intercalation will become a general way to design magnetoelectric and spintronic functional materials. |
Monday, March 4, 2019 5:06PM - 5:18PM |
C02.00012: Magnetoelectric coupling effect in a new multiferroic RbFe(SO4)2 Junjie Yang In the past decade, intense efforts have been directed at the discovery of new multiferroic materials. To search new multiferroic materials, a lot of researches have been focusing on frustrated magnets which usually have complicated magnetic structure. For example, multiferroicity has been discovered in a triangular lattice antiferromagnet RbFe(MoO4)2. Recently we successfully grew high quality single crystals of RbFe(SO4)2 which is isostructural to the multiferroic RbFe(MoO4)2. In this work, we will discuss the ferroelectric polarization, dielectric constant and strong magnetoelectric coupling effect in RbFe(SO4)2 single crystals. |
Monday, March 4, 2019 5:18PM - 5:30PM |
C02.00013: Loss of spin polarization of tunnelling currents due to electrostatic screening at magnetoresistive ferromagnet/ferroelectric tunnel junctions Ibrahim Misirlioglu, Canhan Sen, Wael Aldulaimi, Omid Moradi Magnetoelectric coupling inherent to the bulk of multiferroic films or control of spin orientation in magnetic layers via piezoelectric strain in composite layers have been two forthcoming approaches to enable electric control of magnetic order. Spin-dependent screening occuring at dielectric/ferromagnet interfaces is another magnetoelectric effect important for spin selective tunnel junctions. Here, we analyze the spin-dependent screening of ferroelectric polarization in a film interfacing ferromagnetic electrodes using the continuity equations. We show that local spin population (LSP) in spin subbands near the interfaces can dramatically deviate from bulk, which is in qualitative agreement with recent first principles results. We compute the tunneling currents for majority and minority spins using the Wentzel-Kramers-Brillouin approximation and demonstrate that spin polarization tends to disappear for increasing values of ferroelectric polarization in direct connection with the increase in subband LSP for minority spins. We argue that the reduction in TMR due to spin mixing at the interfaces will be much more prominent in comparison to defect scattering and magnon-driven losses in spin polarization. |
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