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 V38: Spin Waves and DynamicsFocus Live
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Sponsoring Units: GMAG DMP FIAP Chair: Peng Yan, University of Electronic Science and Technology of China |
Thursday, March 18, 2021 3:00PM - 3:12PM Live |
V38.00001: Real-time Hall-effect detection of current-induced magnetization dynamics in ferrimagnets Giacomo Sala, Viola Krizakova, Eva Grimaldi, Charles-Henri Lambert, Thibaut Devolder, Pietro Gambardella Hall effects are ubiquitous in electronic systems and are essential tools for studying the physics of condensed-matter systems and spintronic devices. However, the real-time detection of their dynamics has been impeded by the inherent small magnitude of the Hall signals. |
Thursday, March 18, 2021 3:12PM - 3:24PM Live |
V38.00002: Magneto-Optical Studies of Static and Dynamic Spin Alignment in Ferrimagnetic Thin Films Hengzhou Liu, Jenae Shoup, Durga Khadka, Tilak Ram Thapaliya, Sunxiang Huang, Denis Karaiskaj, Dario Arena We investigate a series of ferrimagnetic thin film samples consisting of (FeCo)1-xGdx and Fe1-xGdx where the Gd content was varied to modify magnetic parameters. The ferrimagnetism arises from the anti-ferromagnetic alignment of the Gd and transition metal (TM) moments. A magnetic compensation occurs at room temperature (RT). Low energy magneto-optical Kerr effect (MOKE) probes only the TM states near the Fermi level. For Fe-rich samples, the hysteresis loop is aligned with the external field while Gd-rich samples display a reversed loop. The coercivity of the films diverges when the magnetic sub-lattices are compensated. We use pump-probe time-resolved MOKE (tr-MOKE) to examine the role of compensation on spin dynamics. All samples exhibit a sharp change in TR-MOKE signal at short (~1 ps) timescales, confirming the demagnetization. The sign of the magnetization reverses across compensation, as observed in the static MOKE. Longer timescales reveal precessional oscillation signals that increase in frequency with increasing external magnetic field. The data are analyzed to extract magnetization and damping values, as well as the gyromagnetic ratio. |
Thursday, March 18, 2021 3:24PM - 3:36PM Live |
V38.00003: Surface properties influence on spin wave modes of ferromagnetic films Rodrigo Arias, Ignacio Armijo The frequencies of propagating spin waves in ferromagnetic films may be determined experimentally with some precision, and reflect the surface properties of the films. For example, if the surface properties break symmetries between both surfaces, there will be frequency non reciprocity between spin waves that travel in different directions. Thus, in order to relate films surface properties to the behavior of spin waves, we study theoretically, within the micro magnetic approximation, spin wave modes under obliquely applied magnetic fields to the film, since in this case the surface properties have a more clear influence in the spin wave properties. For this case the equilibrium magnetization is non-uniform, it deflects close to the surfaces due to effective surface boundary conditions that model local surface fields. We use the Extinction-Green theorems to determine the spin wave modes, solving numerically differential equations along the transverse direction for the so called auxiliary functions. We are aided in the obtention and interpretation of these numerical results by use of the WKB approximation and Boundary Layer methods. |
Thursday, March 18, 2021 3:36PM - 3:48PM Live |
V38.00004: Tuneable, Rare-Earth Free, Synthetic Ferrimagnets for Optical Switching Jade Scott, William Hendren, Robert Bowman, Robert J Hicken, Maciej Dabrowski, David Burn, Gerrit Van der Laan, Andreas Frisk, Alpha N'Diaye Synthetic ferrimagnets (SFM) are of particular interest as feasible media for all optical magnetic switching (AOS) [1]. SFM design requires knowledge and control of the magnetisation, M(T), and anisotropy, K(T), of each ferromagnetic layer, and the exchange coupling between them, Jij(T). We have shown it is possible to engineer the magnetic properties of a series of compensating Ni3Pt/Ir/Co SFM exhibiting perpendicular magnetic anisotropy (PMA). The tuneability of this structure provides an ideal system to investigate the effect of M(T), K(T) and Jij(T) on reversal mechanisms within SFM, with distinct magnetic species allowing for element and layer specific characterisation. Initial pump/probe experiments reveal that it is possible to switch these SFM by application of optical laser pulses under a small applied field. AOS likely requires stronger antiferromagnetic exchange coupling than can currently be achieved in Ni3Pt/Ir/Co SFM. A solution is to replace Ni3Pt with a Ni/Pt multilayer, improving exchange coupling, maintaining element specificity, PMA and tuneability. [1] Nature Mat. 13, 286 (2014) |
Thursday, March 18, 2021 3:48PM - 4:00PM Live |
V38.00005: Quasiparticle and Spin Dynamics in MnBi2Te4 using time-resolved magneto-optical Kerr spectroscopy. Maxwell Poore, Peter Kim, Hari Padmanabhan, Vladimir A Stoica, Seng Huat Lee, Zhiqiang Mao, Venkatraman Gopalan, Richard Averitt Using ultrafast optical spectroscopy, we have investigated quasiparticle and spin dynamics in MnBi2Te4, an intrinsic magnetic topological insulator that exhibits A-type anti-ferromagnetism at TN=24K. The dynamics were measured as a function of temperature and magnetic field using femtosecond optical-pump, near-IR measurements of the reflectivity and magneto-optical Kerr effect (MOKE). The time-resolved MOKE measurements reveal coherent spin precession (~7GHz) in the canted AFM phase which softens with increasing fluence or increasing temperature. In this presentation, we will delineate the field, fluence, and temperature dependence of the long time dynamics in this enigmatic antiferromagnetic topological insulator. |
Thursday, March 18, 2021 4:00PM - 4:36PM Live |
V38.00006: Interactions between spin wave and magnetic domain structures Invited Speaker: Luqiao Liu Spin waves are considered as promising candidate for realizing compact wave-based computing. Recently quite a lot of research efforts have been spent to explore the interactions between spin wave and magnetic domain structures, with the goal of realizing efficient modulation of spin wave propagation. Particularly, spin wave transmission along or across the wall between different magnetic domains have been studied experimentally, numerically and analytically. In this talk, I will describe our recent experimental activities on investigating the mutual interactions between magnetic domain wall and spin wave, where magnetic domain walls manipulate the phase and magnitude of spin wave, and a strong spin wave in turn moves the position of magnetic domain walls [1]. These mutual interactions can potentially provide the possibility of realizing all-magnon spintronic devices. |
Thursday, March 18, 2021 4:36PM - 4:48PM Live |
V38.00007: Wavelength-dependence of the spin-orbit optical properties of Au Víctor H Ortiz, Sinisah Coh, Richard B Wilson Spin-orbit coupling affects the interaction of a metal’s electrons with electromagnetic fields and gives rise to transport phenomena such as the spin Hall effect and the inverse Faraday effect. To date, most experimental research into spin-orbit transport properties in non-magnetic metals has focused on the response to DC electric fields. Here, we report the results of experimental measurements of spin-orbit properties of Au at optical frequencies. We perform time-resolved Magneto optic Kerr effect (TR-MOKE) measurements on Au/Co heterostructures. Ultrafast optical excitation of the cobalt layer drives spin accumulation into an adjacent Au layer that is ~200 nm thick. The spin accumulation, together with spin-orbit coupling, leads to non-zero terms in the off-diagonal conductivity tensor. To measure these off-diagonal terms, we measure the polar MOKE of the Au as a function of wavelength. Our experimental data for wavelengths between 380 and 1030 nm are in agreement with density-functional theory predictions. |
Thursday, March 18, 2021 4:48PM - 5:00PM Live |
V38.00008: Ultrafast Magnetic Spectroscopy and Scattering Using Tabletop High Harmonic Sources Peter Johnsen, Sinead Annie Ryan, Christian Gentry, Emma Cating-Subramanian, Henry C Kapteyn, Margaret Murnane The measurement and control of nanoscale spin dynamics is essential for the understanding and development of quantum materials. We present spectroscopy and scattering measurements of nanomagnetic materials using EUV high harmonic sources. Our control of EUV polarization, spin and orbital angular momentum, along with high spatial and temporal coherence, allows us to uniquely control and probe spin dynamics on few-femtosecond timescales on up. Recent experimental improvements have dramatically reduced the noise of our EUV sources, allowing us to make precise measurements of ultrafast magnetic phenomena. |
Thursday, March 18, 2021 5:00PM - 5:36PM Live |
V38.00009: Optical spin-orbit torque and its application for spin-wave excitation Invited Speaker: Gyung-Min Choi Spin current generation through the spin-orbit interaction in non-magnetic materials lies at the heart of spintronics. In particular, the electrical generation of a spin-orbit torque through the spin Hall effect in heavy metals and Rashba effect in interfaces is intensively studied. For the fast magnetization dynamics, however, the optical generation of a spin-orbit torque is more promising than its electrical counterpart. |
Thursday, March 18, 2021 5:36PM - 5:48PM Live |
V38.00010: Measurement of Current Induce Spin Orbit Torque effects using Optical Ferromagnetic Resonance Bharat Grover, Binoy Krishna Hazra, Banabir Pal, Tianping Ma, Samiran Choudhury, Jae Chun Jeon, Nirel Bernstein, Amir Capua, Stuart Parkin Pure spin current is a flow of spin angular momentum with no net charge current associated with it and is a key ingredient in Spintronics [1]. In the spin Hall effect (SHE) a charge current is converted into a pure spin current. Measurement of spin currents in a material is usually indirect and challenging. Here we discuss a novel optical technique called the optically detected ferromagnetic resonance (O-FMR) to measure the spin Hall angle (SHA) in a conventional Py|Pt bilayer system [2]. We employ the damping modulation method in our optical technique to determine the SHA. We compare our results to the ones obtained by the analogous electrical technique called spin torque ferromagnetic resonance (ST-FMR) on the same sample and show that the damping in the O-FMR can be extracted at higher current densities. Thus, the SHA can be more accurately determined indicating a substantially higher noise floor of the STFMR method. Our work leads to better understanding of the limitations of SHE measurements. |
Thursday, March 18, 2021 5:48PM - 6:00PM Live |
V38.00011: Ferrimagnetic Spin Dynamics beyond Ferro- and Antiferro-magnetic Scenarios Mingda Guo, Hantao Zhang, Ran Cheng Ferrimagnets (FIMs) can be operated as antiferromagnets with high frequency while being able to be detected as ferromagnets, providing unique advantages for spintronics applications. It is widely believed that a two-sublattice FIM behaves antiferromagnetically (ferromagnetically) when it approaches (turns away from) the compensation point. We challenge this oversimplified picture by solving the dynamical modes in a simple FIM driven by the exchange interaction, the magnetic anisotropy, and an applied magnetic field. By varying the ratio of sublattice spins, we demonstrate how spin dynamics in FIMs is intrinsically connected to its ferro- and antiferro-magnetic counterparts, and, more importantly, under what conditions FIMs can go beyond these scenarios. |
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