Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session F40: Transport in Magnetic MaterialsFocus
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Sponsoring Units: GMAG DMP Chair: Qiming Shao, University of California, Los Angeles Room: BCEC 208 |
Tuesday, March 5, 2019 11:15AM - 11:51AM |
F40.00001: Current polarity-dependent manipulation of antiferromagnetic domains Invited Speaker: Peter Wadley Antiferromagnetic spintronics offers the potential for ultrahigh speed dynamics, stability against strong magnetic field perturbations, higher component packing density owing to the lack of stray fringing fields, as well as a wider material base and qualitatively new physical phenomena. |
Tuesday, March 5, 2019 11:51AM - 12:03PM |
F40.00002: Dynamic Spin Transport in Antiferromagnetic Insulators: Non-sinusoidal Angular Dependent Spin Pumping in Y3Fe5O12(YIG)/NiO/Pt Trilayers Yang Cheng, Ricardo Zarzuela, Jack T Brangham, Aidan J Lee, Shane White, P Chris Hammel, Yaroslav Tserkovnyak, Fengyuan Yang Antiferromagnets (AF), which usually serve as the passive layer in spintronics research, have recently been found as effective spin transport media in the FMR driven spin pumping measurement. For example, a YIG/Pt bilayer shows that with the insertion of a 1 nm NiO interlayer could enhance the inverse spin Hall voltage (VISHE), which scratches the surface of the promising antiferromagnetic spintronics. Recently, we studied the out-of-plane angular dependence of VISHE in YIG/NiO/Pt heterostructures with different thicknesses of NiO under a large range of temperatures. The appearance of plateaus for VISHE over the out-of-plane field angle is very different from the YIG/Pt bilayer, which should have a sinusoidal dependence. A maximum is even found at around 30° from the surface normal for specific values of NiO thickness and temperature. By modeling the spin structure of NiO under an out-of-plane magnetic field after considering the interplay among the interfacial exchange coupling, the AF easy-plane anisotropy, and the field-induced hard-axis anisotropy in NiO, the main features of the experimental data in the nontrivial angular dependence of the spin pumping in YIG/NiO/Pt trilayers have been reproduced. |
Tuesday, March 5, 2019 12:03PM - 12:15PM |
F40.00003: Spin-Orbit Torque Switching in a Nearly Compensated Heusler Ferrimagnet Joseph Finley, Chia-Hao Lee, Pinshane Huang, Luqiao Liu Ferrimagnetic materials combine the advantages of the low magnetic moment of an antiferromagnet and the easiness of realizing magnetic reading of a ferromagnet. Recently, it was demonstrated that compensated ferrimagnetic half metals can be realized in Heusler alloys, where high spin polarization, zero magnetic moment, and low magnetic damping can be achieved at the same time. In this work, by studying the spin-orbit torque induced switching in the Heusler alloy Mn2Ru1-xGa, we found that efficient current-induced magnetic switching can be achieved in a nearly compensated sample with strong perpendicular anisotropy and large film thickness. Our work demonstrates the possibility of employing compensated Heusler alloys for fast, energy-efficient spintronic devices. |
Tuesday, March 5, 2019 12:15PM - 12:27PM |
F40.00004: Magnetism and Magneto-Electric Transport in Amorphous Cobalt- and Iron-Germanium Thin Films Dinah Simone Bouma, Frank Bruni, Robert Streubel, Xiaoqian M Chen, Sujoy Roy, Noah Kent, Zhanghui Chen, Lin-Wang Wang, Peter Fischer, Stephen Douglas Kevan, Frances Hellman Thin films (65 < t < 100nm) of amorphous cobalt- and iron-germanium (a-CoxGe1-x and a-FexGe1-x) with 0.40 < x < 0.61 exhibit similar electrical resistivity but remarkably different magnetization for a fixed transition metal concentration x. For all compositions investigated, the resistivity depends weakly on temperature but strongly on x, with only slight differentiation between the Fe and Co transition metal species. However, a low-temperature upturn in resistivity associated with resonant impurity scattering is observed in a-FexGe1-x but absent in a-CoxGe1-x, due to their different magnetic properties: where all measured compositions of a-FexGe1-x are itinerant ferromagnets with a Curie temperature that increases with x, a-CoxGe1-x is paramagnetic down to T = 2 K in the same composition range. This behavior parallels these materials’ crystalline cousins: B20 FeGe hosts a rich magnetic phase diagram, while B20 CoGe is paramagnetic thanks to a pseudogap just above the Fermi level in its density of states. The long-range order that enables this explanation in those materials is absent in our amorphous films, leading us to ascribe the magnetic behavior of these alloys to more localized, short-range physics. |
Tuesday, March 5, 2019 12:27PM - 12:39PM |
F40.00005: Parametric resonance in a nanowire spin Hall device Rodrigo Arias, Liu Yang, Alejandro A Jara, Ilya N Krivorotov Parametric resonance is a versatile tool for excitation of spin waves in nano-magnonic devices. Here we present a joint theoretical and experimental study of parametric resonance of magnetization in nanowires made from bilayers of Pt and Permalloy (Py). In this system, damping of spin waves in Py can be tuned via antidamping spin Hall torque arising from electric current in the Pt layer. We report parametric excitation of spin waves driven by microwave current applied to the nanowire, and tuning of the resonance propertied by direct current. Under magnetic field applied perpendicular to the wire axis, we observe parameter excitation of two types of spin wave eigenmodes: bulk and edge modes. Comparison of our theoretical description of parametric resonance of these modes to the experimental data reveals important role played by the Oersted field produced by ac and dc currents for the excitation process. Theoretical analysis of the data allows us to extract information on the spin Hall efficiency in the Pt/Py device as well as on damping parameters of the excited spin wave modes. |
Tuesday, March 5, 2019 12:39PM - 12:51PM |
F40.00006: Reciprocity in diffusive spin-current circuits Yaroslaw Bazaliy, Revaz R. Ramazashvili Similarly to their purely electric counterparts, spintronic circuits may be presented as networks of lumped elements. Due to interplay between spin and charge currents, each element is described by a matrix conductance. We establish reciprocity relations between the entries of the conductance matrix of a multi-terminal linear device, comprising normal metallic and strong ferromagnetic elements with spin-inactive interfaces between them. In particular, reciprocity equates the spin transmissions through a two-terminal element in the opposite directions. When applied to ``geometric spin ratchets'', reciprocity shows that certain effects, announced for such devices, are, in fact, impossible. Finally, we discuss the relation between our work and the spintronic circuit theory formalism. |
Tuesday, March 5, 2019 12:51PM - 1:03PM |
F40.00007: Spin torques' effects on topological defects and transitions of magnetic domain phases in Ta/CoFeB/MgO Kang Wang, Lijuan Qian, See-Chen Ying, Gang Xiao, Xiaoshan Wu We experimentally study the spin current-driven transitions of magnetic domain patterns in a prototypical multilayer stack of Ta/CoFeB/MgO. The transition processes are demonstrated to be greatly related to responses of topological defects to the spin orbit torque. A moderate perpendicular magnetic field favors stripe domains in the ferromagnetic layer; however, the stripes are cut into dense skyrmions with applying current pulses, where half-skyrmions at the ends of stripes have been proposed to be important. More types of topological excitations are observed in labyrinthine domain patterns at a zero magnetic field. The topological defects can be deleted/generated by spin current with lower/higher current densities. The current-induced deletion/generation of topological defects leads labyrinthine domains to transform into phases with a strong/weak orientational order. We conclude from a derived Thiele equation and micromagnetic simulations that both the current-driven motion of topological defects and magnetization manipulations at domain walls are of significance in current-induced transitions. |
Tuesday, March 5, 2019 1:03PM - 1:15PM |
F40.00008: Activation barriers for creation and annihilation of magnetic droplet solitons Gabriel Chaves-O'Flynn, Daniel L Stein, Andrew D Kent Droplet solitons are magnetization fluctuations that preserve their shape as they precess with uniform frequency ω=0. They satisfy a delicate balance between anisotropy and exchange interactions, and decay in the presence of dissipation. To prevent this, a spin polarized current σ can be applied via a nanocontact of radius ρ*. The magnitude of the current can be increased to induce switching between uniform precession at the ferromagnetic resonance frequency (ω=1), and a stable precession at a frequency larger than the Zeeman frequency (ω=0, in zero applied field). |
Tuesday, March 5, 2019 1:15PM - 1:27PM |
F40.00009: Effect of magnetic tunneling layer in van der Waals Josephson Junction Hiroshi Idzuchi, Ken Harada, Ko-Fan Huang, Na Hyun Jo, Daisuke Shindo, Paul Canfield, Philip Kim Van der Waals (vdW) material has been attracted much attention recently because of their unique features including the accessibility to atomically thin and flat single-crystalline heterostructure. The two-dimensional (2D) nature of these heterointerfaces often enhances the quantum effect. Here, we report vdW ferromagnet can provide a unique opportunity to study the interplay of superconductivity and magnetism. We fabricated a ferromagnetic tunneling device consisting of vdW ferromagnet and superconductor. We observed that the devices exhibit Josephson coupling through magnetic tunneling across 1-6 atomic unit cell thick ferromagnetic insulating layers. Our observation is in contrast with the lack of Josephson coupling reported across traditional ferromagnetic insulating materials such as EuS. We also observed that our superconductor/ferromagnet hybrid devices show the hysteretic critical current against magnetic field sweep. The observed hysteresis differs from the one expected from the coercive field of the ferromagnet. Further study on magnetic structure and switching current distribution indicates the observed phenomena arisen from the interplay between magnetic domain and superconducting vortex structures. |
Tuesday, March 5, 2019 1:27PM - 1:39PM |
F40.00010: Noncollinear Spin Torque Effect in Magnetic Heterojunctions: Combined First-Principles Calculation and TB-NEGF Method Bao-Huei Huang, Chia-Chia Chao, Yu-Hui Tang, Chao-Cheng Kaun In this study, our newly developed “JunPy” [1] package has successfully combined the self-consistent Hamiltonian by using the first-principles calculation [2], including multi-band dispersion relation and complicated interfacial coupling, with the TB model and the non-equilibrium Green’s function (NEGF) method to investigate the noncollinear magnetotransport properties in nm-scale magnetic heterojunctions. This program is first testified by the spin-polarized currents and the noncollinear spin torque effect in conventional Fe/MgO/Fe MTJ. We further employed it to predictthe giant field-like spin torque (FLST) effect in the amine-ended single-molecule magnetic junction [3], which may open a new avenue formultifunctional manipulation in next-generation organicFLST-MRAMs with lower power consumption. |
Tuesday, March 5, 2019 1:39PM - 1:51PM |
F40.00011: Double Tunnel Junction Experiments With Asymmetric Barriers Leonardo Rios E, Edgar Patino, Denis Chevallier Magnetic tunnel junctions constitute a research area of great promise due to its potential application in faster and non-volatile memories. Current studies on Magnetic Tunnel Junctions (MTJ) are abundant for different magnetic and insulator materials. Nevertheless, available references for Double Magnetic Tunnel Junctions (DMTJ) are scarce. Previous studies on Tunneling Magnetoresistance (TMR) Oscillations in DMTJ indicate that asymmetry in the potential barriers is a significant aspect for controlling the TMR. |
Tuesday, March 5, 2019 1:51PM - 2:03PM |
F40.00012: Low frequency noise in MgO magnetic tunnel junctions with magnetic flux concentrator Yiou Zhang, Guanyang He, Gang Xiao Magnetic tunnel junctions (MTJ) have been widely studied as ultra-sensitive magnetic sensors, due to their high sensitivity, low power consumption, and small size. Field detectability of MTJ sensor, particularly at low frequency, is primarily limited by its intrinsic 1/f noise. Hence understanding in the noise performance of MTJ sensor is important for its application. Also, magnetic flux concentrator can enhance signal level of MTJ sensor, yet its role in the noise performance of the sensor system is not fully investigated. In this work, we have measured sensitivity and low-frequency noise spectrum (1 Hz – 10 kHz) of MgO-based MTJ sensor incorporated with an on-chip magnetic flux concentrator. We have found that 1/f noise strongly depends on the bias magnetic field, and a linear relationship between 1/f noise and sensitivity is observed. This result indicates that 1/f noise in highly-sensitive MTJ sensor is dominated by magnetic noise, originated from thermal magnetic fluctuations. Role of magnetic flux concentrator in noise performance will also be discussed. |
Tuesday, March 5, 2019 2:03PM - 2:15PM |
F40.00013: All-electrical control of spin transport in a three-terminal yttrium iron garnet/platinum nanostructure Matthias Althammer, Tobias Wimmer, Stephan Geprägs, Mathias Weiler, Rudolf Gross, Hans Huebl Pure spin currents, i.e. the flow of angular momentum without an accompanying charge current represents a new paradigm in the field of spintronics. Most importantly, pure spin currents can be transported by fermions, i.e. by electrons, in electrical conductors as well as by bosons, i.e. by quantized magnetic excitations, in magnetically ordered insulators. Interestingly, heterostructures consisting of spin-orbit coupled metals with magnetically ordered insulators allow to investigate pure spin current transport in both regimes and their interconversion at the interface [1]. We here report on the control of magnon spin currents via a DC charge current injected pure spin current. To this end, we utilize three electrically isolated platinum (Pt) electrodes deposited on an ultrathin yttrium iron garnet (YIG) film. Employing all-electrical injection and detection mechanisms, we provide evidence for efficient spin transport manipulation by a DC charge current in these devices. Moreover, we discuss the physical origin of non-linear effects in such structures. |
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