Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session H40: Complex Oxide Films and Heterostructures II: Iridates and MultiferroicsFocus
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Sponsoring Units: GMAG DMP DCOMP Chair: Yayoi Takamura, University of California, Davis Room: BCEC 208 |
Tuesday, March 5, 2019 2:30PM - 3:06PM |
H40.00001: Controllable emergent 2D quantum antiferromagnetism realized in iridate-based heterostructures Invited Speaker: Jian Liu The physics of a square lattice of pseudospin-half electrons in layered iridates has been shown to be particularly rich, giving rise to a novel playground for some of the most outstanding and challenging problems in condensed matter physics, such as metal-insulator transition and quantum magnetism. Significant interests have been focused on the analogy with high-Tc cuprates due to the appealing electronic and magnetic similarities with the CuO2 plane despite the much larger spin-orbit coupling (SOC) of Ir. However, unlike the large material family of cuprates, studies on the layered iridates have been limited to a few Ruddlesden-Popper compounds. This talk will discuss our recent work on overcoming this bottleneck by constructing different artificial variants of the two-dimensional (2D) lattice with heteroepitaxial growth of perovskite iridate. By tuning the layer dimension and the quantum confinement structure, our results show that the magnetic order and exchange interactions of the pseudospin are highly sensitive to the lattice degrees of freedom. By leveraging this structural control, we demonstrate a giant response of the 2D antiferromagnetic order to a sub-Tesla external field. This effect manifests a hidden spin rotational symmetry, which was originally proposed for the CuO2 plane but never observed due to the lack of SOC, illustrating the power of atomic layering in exploring and revealing the intriguing SOC-driven emergent behavior beyond the cuprate phenomenology. |
Tuesday, March 5, 2019 3:06PM - 3:18PM |
H40.00002: Tuning electronic and magnetic states of pseudospin-½ square lattice in artificial iridate superlattice Junyi Yang, Lin Hao, Derek Meyers, Han Zhang, Haixuan Xu, Mark Dean, Jian Liu The discovery of Jeff=1/2 Mott insulating state in the Sr2IrO4 has drawn a lot of attention since this 2D pseudospin-1/2 square lattice is analogous to high-Tc cuprates. On the other hand, the emergent phenomena exhibited by the pseudospin-1/2 electrons could be highly susceptible to small changes in the structural degrees of freedom due to the cooperation between electronic correlation and spin-orbit coupling (SOC). Engineering a layered structure of pseudospin-1/2 square lattice in artificial superlattices can afford extra tunability of the electronic and magnetic interactions for stabilizing novel collective quantum states. Through controlling dimensionality, spacing layer and epitaxial strain in perovskite iridate-based superlattices, we have investigated the evolution of the spin-orbit-entangled electronic and magnetic ground state under different control parameters. The results from a suite of characterizations, including transport measurements, magnetometry, and synchrotron-based x-ray spectroscopy and scattering, reveal new routes to drive the collective behavior of the interacting pseudospin-1/2 electrons, which is not achievable in the bulk. |
Tuesday, March 5, 2019 3:18PM - 3:30PM |
H40.00003: Metal insulator transition in SrIrO3 Ultra-Thin Films examined by ionic liquid gating Fernando Gallego, Javier Tornos, Fabian Cuellar, Mariona Cabero, Alberto Rivera-Calzada, Juan I. Beltran, M. Carmen Muñoz, F.J. Mompean, Mar García-Hernández, Carlos Leon, Jacobo Santamaria Perovskite SrIrO3 (SIO) is a narrow-band semimetal, which combines strong spin-orbit coupling and electron correlations. This system has attracted much attention because it is at the verge of a Mott transition. Epitaxial SIO ultra-thin-layers show a thickness dependent metal-insulator transition (MIT) which is controlled by strain. The insulating state exhibits a strong temperature dependence of the resistance, hysteretic-magnetoresistance and anomalous Hall effect at low temperature, indicating ferromagnetic order. We have explored MIT in SIO ultrathin-layers by using Electric Double Layer (EDL) techniques, that employ ionic liquid as gate dielectric. We have simultaneously measured longitudinal (magneto) resistance and Hall effect across this transition to address whether the MIT is band-width or carrier-density-controlled. |
(Author Not Attending)
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H40.00004: Probing Skyrmion Phases in SrIrO3/SrRuO3 thin film by Topological Hall Minor Loops Keng-Yuan Meng, Adam Ahmed, Bryan D. Esser, Jose Flores, David W. McComb, Fengyuan Yang Skyrmions are topological quasi-particles promising for next generation magnetic storage devices. Fundamental understanding of how field history affects skyrmion formation in host materials is vital in regards to technological application. Topological Hall effect is one of major techniques in probing the skyrmion formation. Magnetization and Hall minor hysteresis loops could reveal critical information in addition to traditional full loops. Here we show Hall minor loops of a SrIrO3/SrRuO3 bilayer, which host nanoscale skyrmions as revealed by pronounced topological Hall effect. At low temperature Hall minor loops track the magnetization reversal process, indicating that the skyrmion formation is closely related to magnetization reversal. However, at high temperatures, the Hall resistivity switches before reaching zero field induced by the dominant topological Hall effect; furthermore, the Hall minor loops reveal truly novel behavior that significantly deviates from the magnetization minor loops. We propose such behaviors could due to stabilization of skyrmions even when applied field is larger than magnetization coercive field. |
Tuesday, March 5, 2019 3:42PM - 3:54PM |
H40.00005: Giant magnetic response of a two-dimensional antiferromagnetic iridate Lin Hao, Derek Meyers, Hidemaro Suwa, Junyi Yang, tamene R. Dasa, Haixuan Xu, Cristian Batista, Mark Dean, Jian Liu Layered iridates are featured of preserving a hidden SU(2) symmetry such that anisotropic exchange interactions have no contribution to spin anisotropy. Achieving this symmetry, however, is highly challenging because it's necessary to incorporate strong spin-orbit coupling, control the 2D lattice structure, and minimize the interlayer coupling. We solved this issue through top-down design and bottom-up synthesis of SrIrO3 and SrTiO3 superlattices [1] to realize a pseudospin-half antiferromagnetic (AFM) square lattice. We observed giant AFM responses to sub-tesla external fields by exploiting the strong 2D critical fluctuations preserved under the symmetry-invariant exchange anisotropy. The observed field-induced logarithmic increase of the ordering demonstrates a new pathway for the highly efficient control of AFM order [2]. Further investigation on the transport properties suggests a novel coupling between AFM fluctuations and charge fluctuations, highlights the application potential in semiconductor devices. |
Tuesday, March 5, 2019 3:54PM - 4:06PM |
H40.00006: Interfacial symmetry control of the chiral magnetism in iridate-manganite superlattices Elizabeth Skoropata, John A Nichols, Ankur Rastogi, Changhee Sohn, Ryan Desautels, Xiang Gao, Satoshi Okamoto, Matthew Brahlek, Ho Nyung Lee Correlated oxides have been extensively studied due to the diverse physical properties arising from strong 3d electron correlations combined with lattice and orbital degrees of freedom. Recently, progress toward the creation of exotic quantum and topological properties has been led by the synthesis of 5d oxides with strong spin-orbit coupling. We will present our recent work examining the physical properties of high-quality epitaxially grown LaMnO3/SrIrO3 superlattices. By creating large inversion symmetry breaking with different A- and B-sites in LaMnO3/SrIrO3, we obtain an “topological” Hall effect (THE) that results from interface-induced chiral magnetism resulting from interfacial Dzyaloshinskii-Moriya interactions (DMI). We explore the role of interface symmetry to drive the emergence of the THE at 3d/5d oxides by altering DMI at single interfaces. Furthermore, we compare the effects of (atomic) interfacial DMI and extended superlattice symmetry which together are responsible for the total effective DMI that drive the THE. |
Tuesday, March 5, 2019 4:06PM - 4:18PM |
H40.00007: Dynamical multiferroicity Dominik Juraschek In this talk, I present how circularly polarized optical phonons create magnetic moments, reminiscent of atomistic electromagnetic coils. An appealing mechanism for inducing multiferroicity in materials is the generation of electric polarization by a spatially varying magnetization that is coupled to the lattice through the spin-orbit interaction. Here, I describe the reciprocal effect, in which a time-dependent electric polarization induces magnetization even in materials with no existing spin structure. I present a formalism for this dynamical multiferroic effect in the case for which the polarization derives from optical phonons, and estimate the strength of the phonon Zeeman effect, which is the solid-state equivalent of the well-established vibrational Zeeman effect in molecules, using density functional theory. I further show that a recently observed behavior—the resonant excitation of a magnon by optically driven phonons—is described by the formalism. |
Tuesday, March 5, 2019 4:18PM - 4:30PM |
H40.00008: Coupling of single atom magnetic anisotropy to the neighboring electric polarization Jose Martínez Castro, Marten Piantek, Mats Persson, Cyrus F. Hirjibehedin, David Serrate Multiferroic coupling arises when two ferroic order parameters influence each other. The most popular case is the coupling of magnetization and electric polarization, arising from the interaction of magnetic moments with the surrounding localized electrical charges. In this work we address such interaction at the atomic scale. More specifically, we have recently reported that it is possible to use the abrupt compositional discontinuity occurring at a surface to induce biestable electric polarization in ultrathin ionic insulators [Nature Nanotech. 13, 19-23 (2018)]. Scanning Probe Methods are capable to manipulate matter at the atomic scale while probing simultaneously its electronic and magnetic properties. In this way, using ultrathin films of binary rock-salts, we have built the specific structural and compositional environment that provides a bistable electric polarization controlled by an external electric field. We have deposited individual Co atoms onto the rock-salt films and measured their magnetocrystalline anisotropy by means of inelastic electron tunneling spectra. We show that the uniaxial anisotropy can reversibly tuned to two stable values following the electric polarization switching as a consequence of the crystal electric field experienced by the Co atom. |
Tuesday, March 5, 2019 4:30PM - 4:42PM |
H40.00009: Strain-Induced Anisotropy in NiCo2O4 Epitaxial Films Corbyn Mellinger, Jace C Waybright, Xiaozhe Zhang, Xiaoshan Xu The room temperature ferrimagnetic spinel structured NiCo2O4 (NCO) has garnered interest due to its potential applications in high-capacity supercapacitors. Additional applications in spintronics necessitate studies on its magnetic behavior, which comes about from the magnetic Co tetrahedral and mixed Ni/Co octahedral sites. |
Tuesday, March 5, 2019 4:42PM - 4:54PM |
H40.00010: THz spectroscopy of spin waves in multiferroic LiNiPO4 in high magnetic fields Laur Peedu, Toomas Room, Johan Viirok, Urmas Nagel, Dávid Szaller, Sandor Bordacs, Istvan Kezsmarki, Dmytro Kamenskyi, Vilmos Kocsis, Yusuke Tokunaga, Yasujiro Taguchi, Yoshinori Tokura LiNiPO4 belongs to the family of multiferroic lithium-ortho-phosphates where correlation between magnetic and electric dipoles leads to the ac and dc magnetoelectric (ME) effect. Manifestation of the ac ME effect is non-reciprocal directional dichroism which can be probed with ME spin excitations [1]. Thus, the knowledge of the spectrum of spin excitations and their activity is crucial in understanding ME effect. We have measured the THz absorption spectra of spin excitations in single crystals of LiNiPO4 at temperatures below 4K and in high magnetic fields. In the low temperature commensurate phase we have observed magnetic-dipole, electric-dipole and simultaneously magnetic- and electric-dipole active spin waves, a two-magnon bound state, and a two-magnon continuum. Three spin flop transitions are identified for the magnetic field parallel to the magnetic easy axis. Exchange interactions and the single ion anisotropies of a mean-field spin model are determined based on the magnetic field dependence of the spin-wave excitations. |
Tuesday, March 5, 2019 4:54PM - 5:06PM |
H40.00011: Strain-induced tuning of the electronic correlation in t2g transition metal oxide perovskites Bongjae Kim, Peitao Liu, Jan Tomczak, Cesare Franchini Epitaxial strain offers an effective route to tune the physical parameters in transition metal oxides. So far, most studies have focused on the effects of strain on the bandwidths and crystal field splitting, but recent experimental and theoretical works have shown that also the effective Coulomb interaction changes upon structural modifications. This effect is expected to be of paramount importance in current material engineering studies based on epitaxy-based material synthesization. Here, we perform constrained random phase approximation calculations for prototypical oxides with a different occupation of the d shell, LaTiO3 (d1), LaVO3 (d2), and LaCrO3 (d3), and systematically study the evolution of the effective Coulomb interactions (Hubbard U and Hund’s J) when applying epitaxial strain. Surprisingly, we find that the response upon strain is strongly dependent on the material. For LaTiO3, the interaction parameters are determined by the degree of localization of the orbitals, and grow with increasing tensile strain. In contrast, LaCrO3 shows the opposite trend: the interaction parameters shrink upon tensile strain. This is caused by the enhanced screening due to the larger electron filling. LaVO3 shows an intermediate behavior. |
Tuesday, March 5, 2019 5:06PM - 5:18PM |
H40.00012: Effects of strain on the dynamic magnetic properties of europium iron garnet Victor Ortiz, Bassim Arkook, Junxue Li, Wei Yuan, Tang Su, Igor Barsukov, Jing Shi Ferrimagnetic insulators (FMI) have attracted the interest of the spintronic community as a source of pure spin currents and as a medium for long-range magnon spin transport. Among FMI, rare earth iron garnet (REIG) have a plethora of attributes desirable for practical applications. Epitaxial growth of REIG thin films offers an opportunity to control the magnetic properties; in the case of europium iron garnet (EuIG), the role of Eu for tuning magnetic properties remains elusive. In this work, we present an experimental study on the effect of strain in EuIG thin films on the dynamic magnetic properties. EuIG films of varying thickness (10-100 nm) were grown on various (111) garnet substrates by pulsed laser deposition. The strain was controlled by film thickness and substrate used, as characterized by X-ray diffraction. We performed angular and frequency dependent ferromagnetic resonance measurements on the samples and found a systematic increase in the values of Gilbert damping α and inhomogeneous linewidth ΔHo and the appearance of higher order anisotropies when a large strain is exerted in the films. |
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