Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session D42: Emergent Magnetism in Oxide Films and HeterostructuresFocus
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Sponsoring Units: GMAG DMP DCOMP Chair: Roopali Kukreja, University of California, Davis Room: 709/711 |
Monday, March 2, 2020 2:30PM - 3:06PM |
D42.00001: Magneto-Ionic Control of Heterostructures and Interfaces Invited Speaker: Kai Liu Magneto-ionic approaches for modifying ion distributions in metal/oxide heterostructures offer exciting potentials to control material properties. Our recent studies show that such magneto-ionic effect, even though initiated at metal/oxide interfaces, can extend deep into the rest of the oxide films and drastically tailor their physical properties [1-4]. |
Monday, March 2, 2020 3:06PM - 3:18PM |
D42.00002: Tuning Electrochemical Response in Ion-Gel-Gated La1-xSrxCoO3-δ Films via Sr-doping and strain VIPUL CHATURVEDI, William M Postiglione, Biqiong Yu, Wojciech Tabis, Sajna Hameed, Nikolaos Biniskos, Hua Zhou, Zhan Zhang, Martin Greven, Chris Leighton Electrolyte gating has proven powerful for controlling electronic, magnetic, and optical properties of materials such as oxides. Understanding the true gating mechanisms (i.e., electrostatic vs. electrochemical), however, particularly in oxides, where O vacancy formation and diffusion is often facile, remains challenging. Here, we present a study of the Sr-doping and strain dependence of the ion-gel gate response of La1-xSrxCoO3-δ (LSCO) films (0 < x < 0.7), using transport, magnetometry, and operando synchrotron X-ray diffraction. Consistent with prior work, small negative gate biases induce reversible electrostatic hole accumulation, whereas positive biases induce oxygen vacancies (VO) [1,2]. The window of reversibility and bias threshold for VO formation are found to systematically decrease with x, consistent with higher electrochemical activity of Co4+ than Co3+; tensile strain similarly promotes electrochemical response. At sufficiently high x, a topotactic transformation to a brownmillerite phase occurs. These findings are placed in the context of prior literature and discussed in terms of x-dependent variations in VO formation enthalpy and diffusivity. |
Monday, March 2, 2020 3:18PM - 3:30PM |
D42.00003: Insight into the Electronic Phase Separation in Perovskite Manganites: The Role of Charge-Orbital Ordering in the Interface Region Zhe Wang, Ruqian Wu The electronic phase separation in perovskite manganites, with coexistence of ferromagnetic (FM) metallic and antiferromagnetic (AFM) insulating phase, provides possibilities for tuning their electronic and transport properties. However, the mechanisms that drive the electronic phase separation are still unclear. Using density functional theory calculations, we investigated the charge-orbital ordering (COO) in both the AFM and FM/AFM interface regions of La1-xSrxMnO3 (LSMO). We found that the interface region prefers a distinct COO phase compared with the AFM region, which facilitates the formation of FM/AFM domain boundaries. We further studied the thickness dependent COO phase transition in LSMO ultrathin film, and predicted its critical thickness of phase separation. The results are in well agreement with experiments. These findings suggest that the COO phase transition in the FM/AFM interface region plays a key role in the electronic phase separation. The influence of substrate strain and Sr doping level on the phase separation were also studied. |
Monday, March 2, 2020 3:30PM - 4:06PM |
D42.00004: Engineering Magnetic Interactions in Complex Oxide Heterostructures Invited Speaker: Yayoi Takamura Complex oxides possess a wide range of technologically relevant functional properties including ferromagnetism, ferroelectricity, and superconductivity. Furthermore, their interfaces exhibit unexpected functional properties not found in the constituent materials due to structural and chemical changes as well as electronic and magnetic interactions. These unique interfacial effects lead to fundamental differences compared to analogous metallic systems. For example, ferromagnetic (FM)/FM interfaces consisting of magnetically hard La0.7Sr0.3CoO3 (LSCO) and soft La0.7Sr0.3MnO3 (LSMO) display exchange-spring behavior where the hard layer pins the moments of the soft layer, however, the hard/soft magnetic interface does not coincide with the chemical interface.1 Rather, an interfacial LSCO layer forms that is characterized by magnetically active Co2+ ions which couple to the soft LSMO layer. The full characterization of the structural and magnetic properties of the LSCO/LSMO bilayers involves synchrotron-radiation and neutron-scattering based techniques as well as high resolution transmission electron microscopy. We find that the proportion of the Co2+ ion-rich LSCO layer and magnitude of exchange bias shift depends sensitively on parameters such as individual layer thicknesses, epitaxial strain state, BO6 octahedral tilt pattern of the underlying substrate, and stacking order of the layers.2 These results demonstrate how the competing interactions in complex oxides enable intriguing opportunities to tailor functional properties for new, versatile, and energy efficient spintronic devices. |
Monday, March 2, 2020 4:06PM - 4:18PM |
D42.00005: High temperature magnetism and charge ordering in multiferroic (LuFeO3)m/(LuFe2O4)1 (m = 3, 7, 9) Shiyu Fan, Hena Das, Kevin Arthur Smith, Alejandro R'ebola, Julia Mundy, Charles Brooks, Megan Holtz, Ramamoorthy Ramesh, David Anthony Muller, Darrell Schlom, Craig J Fennie, Stephen A McGill, Janice Lynn Musfeldt We combined optical spectroscopy, magnetic circular dichroism, and first principles calculations to uncover the microscopic origin of the high temperature magnetism in multiferroic superlattices (LuFeO3)m/(LuFe2O4)1, as well as the charge ordered state in the m = 3 case. Analysis of the dichroic spectra at characteristic energies reveals optical hysteresis loops of different Fe centers. Comparison between coercivity vs temperature curves indicates the bulk magnetization emanates mostly from the LuFe2O4 layer. Spectroscopic signature of the interface demonstrates that the larger Lu distortion only selectively increases the local magnetization of the Fe2+ and Fe3+ sites in the spin-up channel, which strengthens the exchange interaction, increases the total magnetization in the LuFe2O4 layer and enhances TC. Comparison between the calculated and measured dichroic spectra affirms a non-polar charge ordered state in the (3, 1) case. These findings provide a site specific technique to analyze the complex interactions in the materials with multiple magnetic centers, and also broaden the possibilities in the hunt for novel multiferroics with high TC and large magneto-electric coupling constant. |
Monday, March 2, 2020 4:18PM - 4:30PM |
D42.00006: Tunable Perpendicular Magnetic Anisotropy in Multiferroic Oxides Xuezeng Lu, James Rondinelli Here we present design rules to realize electric-field control of perpendicular magnetic anisotropy (PMA) utilizing hybrid improper ferroelectricity by scaffolding simple perovskite oxides into ultrashort period superlattices, (ABO3)1/(A'BO3)1, and in multiferroic AA'BB'O6 double perovskites. The study validates the strategy using first-principles calculations and a single-ion-anisotropy model. We show a change of the magnetic anisotropy from the in-plane to out-of-plane direction occurs in (BiFeO3)1/(LaFeO3)1 and a 50% decrease of the magnetization along the out-of-plane direction occurs in LaYNiMnO6 when a polar-to-nonpolar phase transition is activated with strain. The origin of the PMA control is due to the structural-tunable competitions among the t2g and eg orbital interactions on the magnetic ions arising from relativistic spin-orbital interactions that are susceptible to changes in the oxygen octahedral tilts with the transition. Our results allow us to search rapidly for other promising multiferroics materials with voltage-controlled magnetic anisotropy for applications in low-energy information storage and logic devices. |
Monday, March 2, 2020 4:30PM - 4:42PM |
D42.00007: Prediction of a Giant Magnetoelectric Cross-Caloric Effect Around a Tetracritical Point in Multiferroic SrMnO3 Alexander Edström, Claude Ederer We study the magnetoelectric and electrocaloric response of strain-engineered, multiferroic SrMnO3, using a phenomenological Landau theory with all parameters obtained from first-principles-based calculations. This allows to make realistic semi-quantitative and materials-specific predictions about the magnitude of the corresponding effects. We find that in the vicinity of a tetracritical point, where magnetic and ferroelectric phase boundaries intersect, an electric field has a huge effect on the antiferromagnetic order, corresponding to a magnetoelectric response several orders of magnitude larger than in conventional linear magnetoelectrics. Furthermore, the strong magnetoelectric coupling leads to a magnetic, cross-caloric contribution to the electrocaloric effect, which increases the overall caloric response by about 60%. This opens up new potential applications of antiferromagnetic multiferroics in the context of environmentally friendly solid state cooling technologies. |
Monday, March 2, 2020 4:42PM - 4:54PM |
D42.00008: Effects of Three-Dimensional Strain on LaCoO3 Thin Films Ronaldo Rodriguez, Toyanath Joshi, David P Belanger, David Lederman LaCoO3 films grown on SrTiO3 substrates are known to exhibit a net moment below T = 85 K while the same films grown on LaAlO3 exhibit little to no moment [1]. The underlying mechanisms behind this net moment are poorly understood, but it is speculated that modulation of the Co-O-Co bond angle through epitaxial strain may play a key role. By growing LaCoO3 films on SrTiO3 substrates with a high angle (~ 7-9°) of miscut via pulsed laser deposition (PLD), we have been able to induce epitaxial strain along the in plane and out of plane film axes. In-situ reflection high energy electron diffraction (RHEED) detected layer-by-layer growth. Sample crystallinity and topography were measured using X-ray diffraction and atomic force microscopy, respectively. Magnetometry data were collected both parallel and perpendicular to the SrTiO3 [100] surface, as well as parallel and perpendicular to 5 nm steps induced by the miscut of the substrate. In films of thickness ~3-10 nm grown on high angle miscut SrTiO3 substrates, we measure a strong anisotropic magnetization in the plane where spins are realigned at low magnetic fields. Possible mechanisms will be discussed. |
Monday, March 2, 2020 4:54PM - 5:06PM |
D42.00009: Emergent antiferromagnetism in diamagnetically substituted pseudospin-1/2 iridate thin film Junyi Yang, Lin Hao, Qi Cui, Jiaqi Lin, Lukas Horak, Jenia Karapetrova, Jong Woo Kim, P. J. Ryan, Mark Dean, Jinguang Cheng, Jian Liu Recent developments in 5d transition metal oxides have made it a fertile playground to explore exotic emergent phenomena due to the interplay among charge, orbital, spin degrees of freedom. A prominent example is the quasi-2D layered iridate systems where the electronic and antiferromagnetic states of the pseudospin-1/2 electrons are highly susceptible to changes in the structural degrees of freedom. In contrast, the 3D perovskite iridate SrIrO3 is a nonmagnetic semimetal, which is believed to be topologically protected. Recent study showed magnetic order emerges through chemical substitution with nonmagnetic ions, offering an intriguing planform to explore the cooperation between electronic correlation and strong spin orbit coupling beyond the 2D regime. However, bulk perovskite SrIrO3 only exists in polycrystalline form; thus, we have used epitaxial strain to stabilize nonmagnetic ion substituted SrIrO3 in single crystal quality thin film form. Combined with physical properties measurements and synchrotron-based x-ray diffraction and resonant x-ray magnetic scattering, we can resolve its G-type antiferromagnetic structure and further elucidate the structural modulation of its magnetic properties. |
Monday, March 2, 2020 5:06PM - 5:18PM |
D42.00010: Weyl semimetal thin film Eu1-xSmxTiO3 on LSAT (001): field-polarized long-range order and interfacial ferromagnetism Zach Porter, Ryan Need, Kaveh Ahadi, Yang Zhao, Zhijun Xu, Brian James Kirby, Jeffrey Lynn, Susanne Stemmer, Stephen Wilson EuTiO3 thin films have recently been reported to manifest complex magnetotransport phenomena upon carrier substitution, ranging from symmetry breaking anisotropic magnetoresistance to nonmonotonic anomalous Hall transport. Here we investigate the interplay between magnetism and transport behavior by studying the evolution of magnetic order in thin film samples of biaxially strained and electron-doped EuTiO3 under an applied field. Neutron diffraction reveals that G-type antiferromagnetism is suppressed with the onset of in-plane field-polarized ferromagnetism for insulating, semimetallic, and metallic samples. However, polarized neutron reflectometry further reveals the onset of interfacial ferromagnetism at low fields far below the fully polarized state. The relationship between magnetic order and electron transport behavior associated with the Weyl semimetal phase in these films will be discussed. |
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D42.00011: Emergent Ferromagnetism in Protonated CaRuO3 Shengchun Shen, Pu Yu Manipulating the magnetic ground state in complex oxides represents a main stream of research in condensed matter physics and materials science due to their fundamental importance. Here we report the emergence of an itinerant ferromagnetic state from a paramagnetic metallic CaRuO3 through electrically induced protonation during ionic liquid gating. More importantly, this magnetic transition is accompanied with a structural expansion due to proton intercalation, and both which could be reversibly switched by external voltage. Despite the fact that the ruthenates remains metallic across the magnetic transition, we reveal that the ferromagnetic state is strongly correlated with a non-Fermi liquid toward Fermi liquid transition. The versatile magnetic state in protonated CaRuO3 therefore strongly suggests that the electrically controllable protonation could sever as a novel pathway to manipulate the electronic and magnetic properties in complex oxides. |
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