Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session Y38: Spin Pumping and Spin ResonanceFocus Live
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Sponsoring Units: GMAG DMP FIAP Chair: Ran Cheng, University of California, Riverside |
Friday, March 19, 2021 11:30AM - 11:42AM Live |
Y38.00001: Spin-Orbit-Torque Exchange Resonance in Magnetic Topological Insulators Junyu Tang, Ran Cheng Recent developments in magnetic topological insulators (MTI) opened new scenarios of electric control of magnetization dynamics. We formulate the adiabatic spin-orbit torque (SOT) arising from the topological electrons in MTI as well as its reciprocal effect— topological charge pumping. Because the SOT acts oppositely on two adjacent magnetic layers, an applied AC electric field can drive the resonance of the exchange mode, whose frequency is much higher than the ferromagnetic resonance. Owing to the topological charge pumping, the SOT-induced exchange resonance manifests as a sharp peak in the effective optical admittance, which entails a remarkably weaker energy dissipation compared to the ferromagnetic and antiferromagnetic resonance driven by ordinary SOT. Our result introduces novel functionalities of MTI-based devices. |
Friday, March 19, 2021 11:42AM - 11:54AM Live |
Y38.00002: Coherent spin current amplification by a non-adiabatic interaction. Benjamin Assouline, Marina Brik, Nirel Bernstein, Amir Capua We propose a mechanism for coherent spin current amplification in a solid-state magnetic medium device. The mechanism relies on the non-adiabatic regime in a magnetic media [1-3], in which the energetic balance between a precessing magnetic moment and a driving ac spin current is interrupted. In this mechanism, optical pulses perturb a precessing magnetic moment in the presence of a driving ac field, thus injecting energy into the system. The injected energy manifests in spin pumping current, which coherently adds to the injected spin current. |
Friday, March 19, 2021 11:54AM - 12:06PM Live |
Y38.00003: Improvement in Spin-Torque Ferromagnetic Resonance Using Frequency Modulation Saba Karimeddiny, Daniel C Ralph Spin-torque ferromagnetic resonance (ST-FMR) is the most common method for measuring spin-orbit torques in heterostructures with in-plane magnetic anisotropy. Almost always, amplitude modulation (AM) of the microwave current and homodyne detection are employed to improve the signal-to-noise ratio. Quantitative results can then be calculated either from the amplitudes of the resulting resonant Lorentzian lineshapes (LS) or from the DC-current-induced linewidth modulation (LW); however, the two methods frequently disagree. We show, using a Pt(6 nm)/Py sample series, that the AM causes changes to the resonant lineshape that are not captured by the conventional theoretical models of ST-FMR. If we substitute frequency modulation for the amplitude modulation, the line shapes match the theoretical model much more closely and the LS and LW measurements are brought into agreement. |
Friday, March 19, 2021 12:06PM - 12:18PM Live |
Y38.00004: A Ferromagnetic Resonance Study of Magnetic Properties in Magnetron Sputtered NixFe100-x Thin Films and Multilayers for Shielding Applications. Matthew McMaster, William Hendren, Jade Scott, Robert Bowman Tailoring of electromagnetic properties of synthetic magnetic structures is advantageous for high frequency applications, such as shielding materials in magnetic recording, where characterisation in the gigahertz frequency range is necessary to determine parameters for simulations and aid component design. We present a systematic study of the effect of process conditions and stoichiometry on the ferromagnetic resonance (FMR) and spin wave properties [1][2] of NixFe100-x alloy thin films fabricated by magnetron sputtering. The FMR response and high frequency parameters such as Gilbert damping are particularly affected across the fcc/bcc phase transition, improving with increasing Fe content. Effects of modulating stoichiometry were also studied using bilayer superlattice structures with constant total thickness of the form n[NixFe100-x], where n is the number of bilayers and determines the period of modulation. Compared to single layers of the same net composition, the superlattices were seen to enhance the magnetic properties. [1] Y. Ding. J. Appl. Phys. 96. (2004) [2] Y. V. Khivintsev. J. Appl. Phys. 108 (2010) |
Friday, March 19, 2021 12:18PM - 12:30PM Live |
Y38.00005: Magnetization-Independent Spin Hall Effect in Ferromagnetic Trilayers Joseph Mittelstaedt, Robert Alan Buhrman, Daniel C Ralph The anomalous spin Hall effect, which creates charge-to-spin conversion in metallic ferromagnets, offers an opportunity to generate spin currents for which the spin direction is controllable. Here we report spin-torque ferromagnetic resonance measurements of current-induced torques in ferromagnet-spacer-ferromagnet trilayers consisting of NiFe and Co as our magnetic layers with a Cu spacer, allowing us to clearly separate signals from the different ferromagnetic layers. We observe signals with the symmetry of a magnetization-independent spin Hall effect with spin-to-charge efficiencies as large as 10% in NiFe, which is comparable to heavy metal-ferromagnet bilayers. We also investigate how coupling between the two magnetic layers can affect the resonance lineshapes. Our research provides insight into some of the experimental complications that must be considered when measuring spin-torques in ferromangetic trilayer heterostructures. |
Friday, March 19, 2021 12:30PM - 12:42PM Live |
Y38.00006: Detection of above-NV-frequency ferromagnetic dynamics Brendan McCullian, Ahmed Thabt, Benjamin Gray, Alex Melendez, Michael Wolf, Vladimir Safonov, Denis Pelekhov, Vidya P Bhallamudi, Michael R Page, P Chris Hammel The nitrogen vacancy (NV) spin in diamond can sense magnetic field noise at gigahertz frequencies due to its long spin lifetime and spin dependent fluorescence intensity. Thus far, NV sensing of ferromagnetic noise has had an upper frequency limit since NVs are relaxed by dipole fields from magnons at the NV frequency [1,2]. Here, we use microwaves to drive a low damping ferrite thin film and simultaneously detect conventional microwave absorption and NV fluorescence signals. Driving a spinwave instability in the ferrite film results in relaxation of nearby NV centers even when sufficient static field is applied to the film such that there are no NV-resonant magnon modes [3]. Recent theory [4] suggests that multiple magnons participate in producing NV-resonant magnetic field noise when the magnon population is elevated, which provides a pathway for high frequency magnetization dynamics sensing with NVs. |
Friday, March 19, 2021 12:42PM - 12:54PM Live |
Y38.00007: Influence of Structural Disorder on Magnetic Relaxation in Fe Thin Films Shuang Wu, David Smith, Anish Rai, Michael Clavel, Mantu Hudait, Tim Mewes, Satoru Emori How magnetic relaxation is impacted by the structural properties of thin films is an important open question, especially for practical applications (e.g. spin-torque memories). In this work, we examine magnetic relaxation in polycrystalline and amorphous Fe films grown on different seed layers. Out-of-plane ferromagnetic resonance (FMR) measurements reveal Gilbert damping parameters of ~0.0025 for both polycrystalline and amorphous Fe films thicker than 6 nm. This damping parameter range is in quantitative agreement with that for epitaxial Fe [1], demonstrating that the intrinsic Gilbert damping of Fe is remarkably insensitive to the film structure. The in-plane FMR linewidths of both polycrystalline and amorphous Fe films exhibit distinct nonlinear frequency dependences, which are quantitatively reproduced by a grain-to-grain two-magnon scattering model [2]. However, the effective damping parameters derived from this model differ by up to |
Friday, March 19, 2021 12:54PM - 1:06PM Live |
Y38.00008: Nonlocal Uniform-Mode Ferromagnetic Resonance Spin Pumping Yang Cheng, Aidan J Lee, Guanzhong Wu, Denis Pelekhov, P Chris Hammel, Fengyuan Yang Nonlocal spin transport using lateral structures is attractive for spintronic devices. Typically, a spin current is generated by a ferromagnetic (FM) or a heavy metal (HM) electrode in a nonlocal structure, which can be detected by another FM or HM electrode. Here, we report a new nonlocal spin injection scheme using uniform-mode ferromagnetic resonance (FMR) spin pumping in Pt/ Y3Fe5O12 (YIG) lateral structures. This scheme is enabled by well separated resonant fields of Pt/YIG and bare YIG due to substantial change of anisotropy in YIG films induced by a Pt overlayer, allowing for clearly distinguishable local and nonlocal spin pumping. Our results show that the spin decay length of nonlocal uniform-mode spin pumping in 20 nm YIG films is 2.1 μm at room temperature. The first observation of the nonlocal spin pumping through high efficiency angular momentum transfer from the uniform FMR mode in a resonant region into a nonresonant region opens up a new path for spin current generation, propagation, and detection in future spintronic applications. |
Friday, March 19, 2021 1:06PM - 1:18PM Live |
Y38.00009: Superconductivity-enhanced spin pumping: The role of Andreev resonances Mostafa Tanhayi Ahari, Yaroslav Tserkovnyak We describe a simple hybrid superconductor/ferromagnetic-insulator structure manifesting spin-resolved Andreev bound states in which dynamic magnetization is employed to probe spin related physics. We show that, at low bias and below Tc, the transfer of spin angular momentum pumped by an externally driven ferromagnetic insulator is greatly affected by |
Friday, March 19, 2021 1:18PM - 1:30PM Live |
Y38.00010: Determination of the spin Hall angle by the inverse spin Hall effect and the spin torque ferromagnetic resonance: comparison of methods Ranen Ben-Shalom, Shai Cahana, Nirel Bernstein, Guy Seri, See-Hun Yang, Amir Capua The spin torque ferromagnetic resonance (STFMR) is one of the popular methods for measurement of the spin Hall angle (SHA) and is very easy to implement. However, in order to accurately determine the SHA, the acquired data must be carefully analyzed: extraction of the SHA requires that the resonance linewidth be determined with an accuracy of a fraction of the Oe which is achieved by solving a multi-parameter optimization problem, typically six parameters. Additionally, the STFMR signal often deteriorates when DC current is passed through the device. |
Friday, March 19, 2021 1:30PM - 1:42PM Live |
Y38.00011: Spin pumping in YIG/s-wave superconductor hybrids Santiago Jose Carreira, David Sanchez-Manzano, Victor Rouco, Anke Sander, Sophie Collin, Cecile Carretero, Jacobo Santamaria, Adbelmadjid Anane, Javier E Villegas When a spin current is injected into a superconductor (SC) from an adjacent ferromagnet (F), the efficiency of the spin diffusion will be affected by the opening of the superconducting gap and by spin relaxation mechanisms [1]. As a counterpart, the spin dynamics in the F will also change across the superconducting transition. The study of the magnetization dynamics of the F is thus a useful approach to investigate the spin diffusion in the SC [2]. Under these premises, we combined an s-wave SC with Y3Fe5O12 in a bilayer and studied by ferromagnetic resonance experiments the effects of the superconducting gap on the spin pumping efficiency into the SC, driven by the non-equilibrium magnetization precession of the ferrimagnetic insulator. The magnetization relaxation characterized by the damping parameter is severely reduced below Tc due to the opening of the superconducting gap. We also analyzed the spin to charge conversion by ISHE in the SC. The results will be discussed in terms of the spin sinking properties of s-wave superconductors and diffusion in the SC of spin-polarized quasiparticles. |
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