Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session Y54: Spin Ordering and Control in Oxides, Metals and SurfacesFocus Recordings Available
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Sponsoring Units: GMAG DMP Chair: Nitin Prasad Room: McCormick Place W-476 |
Friday, March 18, 2022 8:00AM - 8:36AM |
Y54.00001: Ultralow Damping Spinel Ferrite Films Grown on Isostructural Substrates Invited Speaker: Arunava Gupta Spinel ferrite thin films have numerous technological applications in areas such as telecommunications, magneto-electric coupling devices and are also promising candidates for future spintronic devices. Films of spinel ferrite such as NiFe2O4 (NFO), grown by both physical and chemical deposition techniques, usually suffer from several structural and magnetic drawbacks, e.g., formation of antiphase boundaries and high magnetic saturation fields. We show that by using substrates having similar crystal structure and low lattice mismatch, one can avoid formation of antiphase boundaries and thereby obtain magnetic properties comparable to bulk single crystal. We used spinel MgGa2O4, CoGa2O4 and ZnGa2O4 substrates, which have 0.6%, 0.1% and 0.05% lattice mismatch, respectively, with NFO to grow epitaxial films that are essentially free of antiphase boundaries and exhibit sharp magnetic hysteresis characteristics. Moreover, ferromagnetic resonance linewidths similar to those in bulk single crystals are obtained with very low damping parameter. We investigated spin transport properties of the NiFe2O4 films grown on the three substrates via the longitudinal spin Seebeck effect (LSSE). An increase in the spin voltage signal with reduction in lattice mismatch is observed, which is in correspondence with similar improvements in structural and magnetic properties. We further demonstrate that bidirectional field-dependent LSSE voltage curves can be utilized to reveal the complete magnetization reversal process, which offers a new vectorial magnetometry technique based on spin caloric effect. |
Friday, March 18, 2022 8:36AM - 8:48AM |
Y54.00002: The Effect of Point Defects on the Compensation Temperature of Terbium Iron Garnet Thin Films Ethan R Rosenberg, Jackson J Bauer, Connor A Occhialini, Jonathan Pelliciari, Richard Rosenberg, John W Freeland, Frank de Groot, Riccardo Comin, Caroline A Ross Recently, rare earth iron garnets (REIG) thin films with perpendicular magnetic anisotropy (PMA) have attracted a great deal of attention for spintronic applications. A subset of REIG materials exhibit magnetic compensation temperatures (Tcomp), which may enable technologically interesting phenomena such as ultrafast domain wall velocities and ultrasmall skyrmions. For example, terbium iron garnet (TbIG) thin films have been grown by pulsed laser deposition with PMA and a Tcomp of ~330 K, and their spin Hall magnetoresistance and spin orbit torque switching characteristics were investigated near compensation. Interestingly, however, the bulk Tcomp of TbIG is closer to 250 K – about 80 K lower than the Tcomp of the films. Hypotheses such as Tb antisites and/or iron vacancies have been suggested but have not been rigorously tested. Explaining this phenomenon could guide future efforts to engineer Tcomp. |
Friday, March 18, 2022 8:48AM - 9:00AM |
Y54.00003: Voltage Induced Strain Control of Perpendicular Magnetic Anisotropy in Yttrium Substituted Dysprosium Iron Garnets Walid Al Misba, Miela Josephine Gross, Dhritiman Bhattacharya, Daniel B Gopman, Caroline A Ross, Jayasimha Atulasimha Voltage control of spintronic devices can be extremely energy efficient, which is useful to perform energy intensive classification tasks in edge devices where power is a constraint [1, 2]. In this study, we perform voltage controlled perpendicular magnetic anisotropy (PMA) modulation in Yttrium substituted Dysprosium Iron Garnet (Y:DyIG) thin film. The film is grown over a piezoelectric substrate PMN-PT where the optimal ratio of Y and DyIG provides low coercivity and high saturation moment. PMA in the film is generated due to strain resulting from thermal mismatch between the film and substrate. Voltages are applied across the thickness of the PMN-PT/SiO2/Y-DyIG heterostructure to pole the piezoelectric along [011] direction (perpendicular to surface). Changes in PMA by applied poling voltages were studied by magnetometry. We report strain-induced modulation of PMA through the magnetoelastic effect. |
Friday, March 18, 2022 9:00AM - 9:12AM |
Y54.00004: Temperature Dependence of Planar Hall Effect and Anisotropic Magnetoresistance in Phase-Separated (La1-yPry)1-xCaxMnO3 Thin Films Ashkan T Paykar, Amlan Biswas Electronic phase coexistence between the ferromagnetic metallic (FMM) and insulating phases of the perovskite manganite (La1-yPry)1-xCaxMnO3 (LPCMO) leads to unique electronic and magnetic properties at low temperatures. In particular, uniaxial, in-plane magnetic anisotropy has been induced in thin films by anisotropic strain from the substrate, (110) NdGaO3 (NGO). However, on the scale of millimeters, the LPCMO thin films do not show clear anisotropic transport or anisotropic magnetoresistance (AMR) associated with the magnetic anisotropy. We have fabricated millimeter scale structures using photolithography to measure both the AMR and planar Hall effect (PHE). The combination of AMR and PHE measurements reveal uniaxial anisotropy at low fields. This anisotropy decreases as the temperature is increased close to the metal-insulator transition temperature. Our data suggest that the uniaxial anisotropy is proportional to the size of the FMM regions in the thin film and not just on the anisotropic strain. PHE measurements are a technique that can also be used to measure the magnetic coercive field and magnetic anisotropy of manganite microstructures. Hence, we can measure the variation of magnetic anisotropy as the sample size is decreased to the scale of phase separation in LPCMO. |
Friday, March 18, 2022 9:12AM - 9:24AM |
Y54.00005: Dynamic in-plane magnetic tunnel junctions formed in manganites using non-uniform-electric-fields Ambika Shakya, Nicole R Burg, Amlan Biswas (La1-yPry)1-xCaxMnO3 (LPCMO) thin films grown on (110) NdGaO3 (NGO) substrates exhibit electronic phase separation between ferromagnetic metallic (FMM) and insulating regions. The FMM regions are of micrometer scale, dynamic, and can be controllable using external electric fields. We have fabricated micrometer-sized gold contact patterns on LPCMO thin films to apply in-plane non-uniform electric fields. We observed that the non-uniform electric fields reorganize the FMM and insulating regions to form in-plane tunnel junctions. At higher temperatures close to the insulator-metal (IM) transition, the dI/dV-V curves show a zero-bias anomaly typically observed in the tunneling spectra of disordered metals. At temperatures about 10 K below the IM transition, a hard gap is observed in the dI/dV-V spectra with a gap value close to the charge-ordering gap in manganites. However, at higher voltages, the conductance shows a sharp and irreversible increase, and subsequent dI/dV-V spectra show quadratic behavior expected from metal-insulator-metal junctions. These electric field-induced tunnel junctions show clear signatures of tunneling magnetoresistance. Our data show that in-plane magnetic anisotropy plays an important role in the formation of these intrinsic tunnel junctions. |
Friday, March 18, 2022 9:24AM - 9:36AM |
Y54.00006: Free coherent evolution of a coupled atomic spin system initialized by electron scattering Lukas M Veldman, Laetitia Farinacci, Alexander F Otte, Rasa Rejali, Markus Ternes, Rik Broekhoven, Jeremie Gobeil, David Coffey Full insight into the dynamics of a coupled quantum system depends on the ability to follow the effect of a local excitation in real-time. Here, we trace the free coherent evolution of a pair of coupled atomic spins by means of scanning tunneling microscopy. Rather than using microwave pulses, we use a direct-current pump-probe scheme to detect the local magnetization after a current-induced excitation performed on one of the spins. By making use of magnetic interaction with the probe tip, we are able to tune the relative precession of the spins. We show that only if their Larmor frequencies match, the two spins can entangle, causing angular momentum to be swapped back and forth. These results provide insight into the locality of electron spin scattering and set the stage for controlled migration of a quantum state through an extended spin lattice. |
Friday, March 18, 2022 9:36AM - 9:48AM |
Y54.00007: Characterization of morphological, electronic and magnetic properties of α−Mn surfaces Ricardo Ruvalcaba, Joseph P Corbett, Noboru Takeuchi, Jonthan Guerrero-Sánchez, Arthur R Smith The α-manganese phase has one of the most complex and unique crystal structures among all metals in the periodic table with a 58 atom basis and a non-collinear antiferromagnetic bulk spin-structure. Manganese is a cornerstone magnetic material for a variety of applications: in dilute magnetic semiconductors, as a rare-earth free magnet, and in magnetic topological insulators to name a few. Despite its prevalence in applied materials as an alloy, little real-space investigations of α-Mn have been performed. We performed a thorough analysis of the surface structures of α-Mn via first principles and scanning tunneling microscopy (STM). We present the most stable surface reconstructions and a description of the atomic arrangements at the surface as showcased by both theoretical and experimental STM images. Analysis of real-space and Fourier transformed STM images help match candidate Terrsoff-Hamann simulation surfaces with experimental STM images. Analysis of electronic band structure and magnetic spin-structures reveals a non-collinear spin structure. Finally, a discussion of the mechanisms that lead to the difference in bulk and surface properties is presented. |
Friday, March 18, 2022 9:48AM - 10:00AM |
Y54.00008: Investigation of the hyperfine interaction of single atoms in a vector magnetic field Laetitia Farinacci, Lukas M Veldman, Philip Willke, Alexander F Otte The combination of electron spin resonance and scanning tunnelling microscopy gives exceptional energy resolution for the investigation of spin-spin interactions on the atomic level [1]. Remarkably, Willke et al. measured the hyperfine interaction of individual atoms on MgO/Ag(001) [2]. They showed that the hyperfine interaction is strongly dependent on the binding site of the investigated atoms, resulting from variations in the electronic ground state of the atoms as well as on various other properties such as the level of mixing with neighbouring atoms and the spatial extent of the nuclear spin wave-function. Here, we provide a full angle-dependent investigation of the measured hyperfine splitting for Ti on MgO/Ag(001) through measurements in a vector magnetic field. We observe a strong anisotropy of the interaction that can be related to the anisotropy of the g-factor which has been highlighted in other studies [3,4]. This gives us unprecedented insight into the electronic ground state configuration of the atoms. |
Friday, March 18, 2022 10:00AM - 10:12AM |
Y54.00009: sp-electron Magnetism in substitutional doped graphene: New insight from first-principles calculations Lilia Meza-Montes, Romeo De Coss, Juan Hernandez-Tecorralco, Miguel Cifuentes Quintal The study of low-dimensional magnetic systems is a relevant subject in basic research for their potential technological applications. Magnetism on defective graphene has been predicted theoretically and observed experimentally during the last years. However, there are open questions about the origin of the magnetic behavior when substitutional impurities with sp electrons are considered. This work is aimed to contribute to the understanding of impurity-induced magnetism in substitutional doped graphene systems. Total energies, electronic band structures, and spin magnetic moments for doped graphene with impurities introducing holes (B, Al, and Ga) and introducing electrons (N, P, As, Sb, and Bi), were obtained using density functional theory. We show that the spontaneous magnetization in the studied systems arises from an electronic instability by the presence of a narrow impurity band at the Fermi level. In addition, we found that the emergence of magnetism requires the impurity to introduce an extra electron to the graphene lattice. Finally, the relationship between the impurity bandwidth and the impurity-carbon hybridization is analyzed, in the arise of sp-electron magnetism in substitutional doped graphene. |
Friday, March 18, 2022 10:12AM - 10:24AM |
Y54.00010: Weak Ferromagnetism in Co-Si Alloys David J Sellmyer, Balamurugan Balasubramanian, Ahsan Ullah, Shah Valloppilly, Ralph Skomski Cobalt-silicon alloys are one of the most intriguing classes of magnetic materials. CoSi and Co2Si are close to ferromagnetism, so that nanostructuring and minor amounts of excess Co can trigger a quantum-phase transition from exchange-enhanced Pauli paramagnetism to weak ferromagnetism. The ferromagnetic states exhibit interesting properties, such as B20-type DM interactions and skyrmionic spin spirals [1, 2]. Our focus is on off-stoichiometric bulk Co2Si, which we investigate experimentally and by model calculations. Depending on the wave-function overlap, there are two limiting types of magnetism, namely ordinary very weak itinerant ferromagnetism (as in ZrZn2) and moments induced by excess Co (similar to 3d impurities in 4d/5d hosts). The two scenarios involve quasiparticles whose Curie constants cannot be analyzed in terms of traditional atomic-scale effective moments, namely ZrZn2-type paramagnons and moments localized around excess Co atoms. The M(H, T) curves convolute random-anisotropy effects, thermal spin disorder, and Stoner excitations, but in both cases, magnetic measurements allow the simultaneous estimation of the two key quantities involved, namely the quasiparticle size and the quasiparticle moment, which we have done for the present system. |
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