Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session M53: Magnetic Thin Films: Strain EffectsFocus Recordings Available
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Sponsoring Units: GMAG Chair: Johanna Nordlander, Harvard Room: McCormick Place W-475B |
Wednesday, March 16, 2022 8:00AM - 8:12AM |
M53.00001: Strain induced Magnetic Anisotropy in Cobalt Vanadate Thin Films Sangsoo Kim, Christie J Thompson, Christianne Beekman Cobalt Vanadate (CoV2O4) is a cubic normal spinel that displays interplay between orbital, magnetic, and structural properties. One aspect of the material is its 90 K tetragonal distortion resulting in a noncollinear ferrimagnetic phase, as evidenced by neutron scattering studies1. To study the effects of structural distortion, CoV2O4 is grown on an (001) SrTiO3 substrate, inducing an in-plane compressive strain that results in an orthorhombic unit cell. For the thin films, magnetometry and neutron scattering measurements2 show that its magnetic easy axis changes from out-of-plane to in-plane upon cooling through 90 K. To explore the temperature evolution of the magnetic anisotropic surface, torque magnetometry is utilized. Of key interest is the large change in magnetic anisotropy at 90 K, below which the field needed to saturate the magnetization along the out-of-plane hard axis increases by an order of magnitude. |
Wednesday, March 16, 2022 8:12AM - 8:24AM |
M53.00002: Near-Room-Temperature Valence-Driven Spin-State/Metal-Insulator Transition in Strain-Tuned (Pr1-yYy)1-xCaxCoO3-δ Films Vipul Chaturvedi, Supriya Ghosh, Patrick Quarterman, Purnima P Balakrishnan, Brian J Kirby, Hua Zhou, Huikai Cheng, Amanda Huon, Timothy R Charlton, Michael Fitzsimmons, William M Postiglione, Andrew Jacobson, John E Dewey, Caroline Korostynski, Javier G Barriocanal, Andre Mkhoyan, Chris Leighton Pr-based cobaltites such as Pr1-xCaxCoO3-δ and (Pr1-yYy)1-xCaxCoO3-δ exhibit remarkable first-order coupled spin-state/metal-insulator/structural transitions driven by a unique Pr valence transition. Such phenomena offer highly appealing device functionality, but have thus far been confined to cryogenic temperatures in bulk materials. Here, we combine epitaxy on multiple substrates with transport, magnetometry, polarized neutron reflectometry, and temperature-dependent synchrotron X-ray diffraction and electron energy loss spectroscopy to demonstrate complete control over the electronic ground state of (Pr1-yYy)1-xCaxCoO3-δ films. Compressive strain realizes enhancement of the spin-state/metal-insulator transition to at least 245 K, with synchrotron diffraction and electron energy loss spectroscopy confirming a Pr/Co valence shift. Conversely, tensile strain stabilizes metallic ferromagnetism with Curie temperature up to 75 K. We thus construct a strain phase diagram, highlighting: (i) potential access to a unique quantum critical point, and (ii) that a room temperature strain-stabilized first-order spin-state/metal-insulator/structural/valence transition is likely within reach in such perovskites. |
Wednesday, March 16, 2022 8:24AM - 8:36AM |
M53.00003: Superconductivity in EuxSr1-xTiO3 films grown by molecular beam epitaxy Nicholas G Combs, Hanbyeol Jeong, Simon Munyan, Arman Rashidi, Susanne Stemmer Electron-doped SrTiO3 is a dilute superconductor which violates standard BCS theory and for which the origin of superconductivity remains unsolved. Numerous studies have suggested a correlation between incipient ferroelectricity and superconductivity. Strained films of SrTiO3 undergo a ferroelectric transition. Their solid solutions with EuTiO3, which exhibits multiferroicity under strain, are interesting because there are multiple quantum critical points. Here, we report on the evolution of superconducting, structural, electronic, and magnetic properties in a series of compressively strained EuxSr1-xTiO3 films grown by molecular beam epitaxy in which the Eu concentration (x) is varied. We demonstrate that superconductivity survives to Eu concentrations greater than 10% and we examine how its subsequent destruction as x is increased correlates with other properties, such as ferroelectricity. We discuss the implications for the superconducting mechanism in this system. |
Wednesday, March 16, 2022 8:36AM - 8:48AM |
M53.00004: Strain Relaxation Effects on the Valence-Driven Spin-State/Metal-Insulator Transition in Epitaxial (Pr1-yYy)1-xCaxCoO3-δ Films John E Dewey, Vipul Chaturvedi, William M Postiglione, Andrew Jacobson, Caroline Korostynski, Chris Leighton Pr-based cobaltites such as Pr1-xCaxCoO3-δ and (Pr1-yYy)1-xCaxCoO3-δ exhibit remarkable first-order coupled spin-state/metal-insulator/structural transitions driven by a unique Pr valence transition. While such phenomena are restricted to cryogenic temperatures in bulk, recent work of ours stabilized a valence transition to Tvt = 245 K in compressively strained (Pr1-yYy)1-xCaxCoO3-δ films. Here, we explore the effects of strain relaxation in such films. Careful analysis of temperature-dependent resistivity reveals splitting of the valence transition into two with increasing film thickness, one at the fully strained Tvt and one at the bulk Tvt. In-plane and out-of-plane lattice parameters from specular X-ray diffraction and asymmetric reciprocal space maps support this picture, evidencing partial strain relaxation with increasing thickness. Remarkably, in the ultrathin limit below ~10 unit cells, Tvt remains constant but the resistivity change across the transition is suppressed, destroying the high-temperature metallic state. We discuss possible origins of this low thickness behavior. Our results shed further light on the strain control of these unique spin-state/metal-insulator/structural/valence transitions. |
Wednesday, March 16, 2022 8:48AM - 9:00AM |
M53.00005: Strain-induced orbital energy shift in antiferromagnetic RuO2 revealed by resonant x-ray scattering Benjamin Gregory, Joerg Strempfer, Jacob Ruf, Daniel B Weinstock, Hari Nair, Yifei Sun, Darrell G Schlom, Kyle M Shen, Andrej Singer In the ruthenium perovskite family, epitaxial strain has been shown to enhance magnetization and tune Tc in superconductors. Recently strain engineering has been shown to induce superconductivity in the previously non-superconducting metal RuO2. Long thought to be an ordinary, paramagnetic metal, neutron and x-ray diffraction have revealed a surprising antiferromagnetic ground state in RuO2 . Here we present a magnetic resonant x-ray scattering (RXS) study of the same RuO2 film specimens used to demonstrate strain-induced superconductivity. At the Ru L2 edge we can access the forbidden magnetic reflection (100) and probe the magnetic ground state, domain sizes and electronic properties. We notably observe a large, strain-dependent shift of Ru eg orbitals to higher energy in the sample that hosts novel superconductivity. |
Wednesday, March 16, 2022 9:00AM - 9:12AM |
M53.00006: Controlling the electronic and magnetic properties by Sn substitution in SrRuO3 epitaxial films Amanda Huon, Sangmoon Yoon, Michael Fitzsimmons, Jong Mok Ok, Timothy R Charlton, Clarina R Dela Cruz, Ho Nyung Lee Controlling the lattice strain in films through chemical substitution has been widely investigated in strongly correlated electronic systems as a means to change electronic and magnetic properties from those of the bulk. Here we present a systematic study on epitaxial SrRu1−xSnxO3 (0 ≤ x ≤ 1) thin films grown by pulsed laser deposition to achieve stable phases in this family of quaternary perovskites, which has been unstable in bulk. We find a gradual expansion of the c-axis lattice parameter with Sn doping, serving as a means to tune chemical pressure and magnetism. This talk will focus on the electronic, magnetic, and magnetotransport properties by the effects of Sn doping in SrRuO3 thin films. |
Wednesday, March 16, 2022 9:12AM - 9:48AM |
M53.00007: Correlated Oxide Dirac Semimetal in the Qantum Limit Invited Speaker: Jong Mok Ok Quantum materials with strong correlation and non-trivial topology are indispensable to next-generation technologies. Exploitation of topological band structure is an ideal starting point to realize correlated topological QMs. In this talk, I will introduce recent discovery of strain-induced correlated topological phase in strained SrNbO3 films. Dirac electrons in strained SrNbO3 films revealed ultra-high mobility (μmax ≈ 100,000 cm2/Vs), exceptionally small effective mass (m* ~ 0.04me), and non-zero Berry phase. More importantly, strained SrNbO3 films reached the extreme quantum limit, exhibiting a sign of fractional quantum states and giant mass enhancement. Our results suggest that symmetry modified SrNbO3 is a rare example of correlated topological QMs, in which strong correlation of Dirac electrons led the realization of fractional occupation of Landau levels |
Wednesday, March 16, 2022 9:48AM - 10:00AM |
M53.00008: Interfacial Magnetization in Ultrathin NiCo2O4 Thin Films Corbyn D Mellinger, Xiao Wang, Richard Rosenberg, Xuemei Cheng, Xiaoshan Xu NiCo2O4 (NCO) films are well-known to exhibit strong perpendicular magnetic anisotropy [1] on account of the epitaxial strain provided by a substrate with small lattice mismatch, e.g. MgAl2O4 (MAO). The conductivity of NCO also lends itself to potential uses in spin-electronic devices, as has already been studied for a NCO/MAO/MAO magnetic tunnel junction [2]. In these cases, the magnetic behavior of the interface is critical to realizing the full potential of such devices. To this end, we have studied the magnetic behavior of NCO films of varying thickness using x-ray magnetic circular dichroism (XMCD). Ultrathin films (t < 4 nm) show features which, through comparison of electron yield and fluorescence yield measurement modes, can be attributed to magnetization at the film-vacuum interface. Further, the surface magnetization persists at a lower transition temperature than for the bulk. Physical mechanisms for this effect will be discussed. |
Wednesday, March 16, 2022 10:00AM - 10:12AM |
M53.00009: Epitaxial strain controlled ferrimagnetic spin compensation in Tm5Fe5O12 films Hasith E Perera, Yanjun Ma, Michael Weinert, Cheng Cen Magnetic iron garnet films with perpendicular magnetic anisotropy (PMA) have found many applications in spintronics and proximity effect-based quantum phase engineering. In this work, we study the effects of epitaxial strain on the structural and magnetic properties of Tm5Fe5O12 (TIG) films grown by pulsed laser deposition (PLD). Samples experiencing different levels of tensile strain are produced by varying the film thickness on different substrates including (111)-oriented Gd3Ga5O12(GGG) and substituted GGG (SGGG). Variable-temperature magneto-optic Kerr effect (MOKE) measurements using both polar and longitudinal configurations are carried out to systematically map out the 3D spin orientations. The observed results reveal a non-colinear ferrimagnetic spin compensation process that is highly strain sensitive. The detailed understanding of the ferrimagnetic spin orientation in TIG thin films bring forward new assets highly useful in the design and engineering of magnetic quantum interfaces. |
Wednesday, March 16, 2022 10:12AM - 10:24AM |
M53.00010: Doping- and Strain-Dependent Electrolyte-Gate-Induced Perovskite to Brownmillerite Transformation in Epitaxial La1-xSrxCoO3-δ Films William M Postiglione, Vipul Chaturvedi, Rohan D Chakraborty, Biqiong Yu, Wojciech Tabis, Sajna Hameed, Nikolaos Biniskos, Andrew Jacobson, Zhan Zhang, Hua Zhou, Martin Greven, Vivian E Ferry, Chris Leighton The reversible topotactic transformation between perovskite (P) SrCoO3-δ and oxygen-vacancy-ordered brownmillerite (BM) SrCoO2.5 has attracted much attention recently due to wide modulation of electronic, magnetic, and optical properties, particularly when voltage-triggered in electrolyte gating. SrCoO3 is relatively unstable, however, and there has been little exploration of alternate compositions. Here, we present the first study of ion-gel-gating-induced P to BM transformations across almost the entire La1-xSrxCoO3-δ phase diagram (0 < x < 0.7). Electronic transport, magnetometry, and operando synchrotron X-ray diffraction establish the P to BM transformation at nearly all x, including x < 0.5, where both P and BM are highly air-stable. The transformation threshold voltage decreases significantly with x, but also with epitaxial strain (both tensile and compressive), providing desirable tunability for devices. These results are analyzed in the context of oxygen vacancy formation energies, diffusion coefficients, and recent theory, establishing that thermodynamics, not kinetics, underpins the decrease of the threshold voltage with x. These findings substantially advance the understanding of this voltage-driven transformation, with both fundamental and technological implications. |
Wednesday, March 16, 2022 10:24AM - 10:36AM Withdrawn |
M53.00011: Real space imaging and temperature tunability of magnetic domain walls in FeTe thin films. Shrinkhala Sharma, Hong Li, Zheng Ren, Ilija Zeljkovic External parameters such as strain and temperature can have pronounced effects on the electronic properties of solids. Here we synthesize thin films of the parent non-superconducting compound of FeTe using molecular beam epitaxy (MBE). We use spin-polarized scanning-tunneling microscopy (SP-STM) to map the local antiferromagnetic (AFM) order as a function of temperature. We observe nanoscale magnetic domains, which shift irreversibly with a rise in temperature. These simultaneously correlate to the local anisotropic strain along the Te-Te direction. Our studies suggest that temperature changes can dramatically change the microscopic profile of AFM domains. We conclude by discussing the implications of our results on the domain wall formation in FeTe. |
Wednesday, March 16, 2022 10:36AM - 10:48AM |
M53.00012: Diffusion studies of H of different charge states and their interplay with Co spin states in SrCoO2.5 Gaofeng Teng, Yupu Wang, Jingzhao Zhang, Junyi Zhu The tunable magnetism and reversible phase transformation have attracted vast research interest in liquid ion gated SrCoO2.5 (SCO). Hydrogen atoms at different charge states may play important roles in the energy and spintronic devices, yet no systematic studies are available. How the hydrogen atoms at different diffusion pathways interplay with the spin states of Co atoms is also unknown. To answer the above questions, we used the climbing-image nudged elastic band method based on spin-polarized DFT to study various diffusion pathways of H at different charge states. The diffusion of proton is slightly faster than atomic H because no significant electron transfers occurs for proton. The fastest pathways of both charge states are near Sr-O layer because the ion of Sr is relatively inert. Due to the different symmetries of different sites along the pathway near the Co-O layers, the electron of the atomic H transfers to different Co sites and lead to magnetic fluctuations. |
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