Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session B42: Ferromagnetic dynamicsFocus

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Sponsoring Units: GMAG Chair: Yi Li, Argonne Natl Lab Room: 709/711 
Monday, March 2, 2020 11:15AM  11:27AM 
B42.00001: Electronic Relaxation Rates in Clean Metalic Ferromagnets James Amarel, Dietrich Belitz, Theodore Kirkpatrick In clean metallic ferromagnets at asymptotically low temperature the magnonexchange contribution to the singleparticle and transport relaxation rates is exponentially suppressed due to the exchange gap [1]. The powerlaw prefactor of the exponential term is difficult to determine since the gap provides an energy scale in addition to the temperature. To answer this question we present an asymptotically exact evaluation of the Kubo formula. Our solution also clarifies the relation between the integral equation inherent in the Kubo formula and the Boltzmann equation. 
Monday, March 2, 2020 11:27AM  11:39AM 
B42.00002: Latent state in timeresolved nonlinear magnon scattering in thin films Tao Qu, Aneesh Venugopal, James M. Etheridge, Paul Crowell, Randall H. Victora The physics of nonlinear magnon scattering has been exploited in nonlinear microwave devices for wireless and satellite communication applications. The latent state, which is the time delay in the response to a microwave pulse, is required to be reduced for fast information communication. We have studied the latent state in timeresolved nonlinear magnon scattering in thin films, in both theory and experiment. The experiment is performed using phasesensitive timeresolved heterodyne ferromagnetic resonance. The theory is a hybrid timeresolved model which uses an analytical equation of motion based on the HolsteinPrimakoff transformation, and realistic micromagnetic simulation, in order to capture the magnon number change caused by the scattering. From the experiment, we find the latent state is a function of power, frequency, and material properties, which indicates the delay time scale is tunable by specific design. The origin of the latent state is the magnon redistribution, in that the uniform magnon mode (wavevector k=0) takes time to scatter into nonuniform magnon modes k≠0, which is reflected in the timeresolved magnon number of these modes. 
Monday, March 2, 2020 11:39AM  11:51AM 
B42.00003: A semianalytical approach for studying the dynamics of magnetic vortices with DzyaloshinskiiMoriya interactions Carla Quispe Flores, Karen Livesey, Kristen S. Buchanan The magnetic vortex provides a convenient system to investigate the effects of the Dzyaloshinskii Moriya interactions (DMIs) on the dynamics of patterned magnetic structures in confined geometries. Here we introduce a LandauLifshitz based diagonalization (LLD) method to calculate the effects of the DMI on radialtype modes in circular disks. The LLD method is a semianalytical approach which diagonalize the magnetostatic kernel, exchange and DMI contributions to extract the system eigenfrequencies and eigenmodes. Our calculations show that the DMI leads to a frequency shift that is comparable to what is observed for extended films, however, only the downshifted mode is observed. The excitation amplitudes are enhanced near the core and the structure edges, and modes with even symmetry that would normally be suppressed for a spatially uniform excitation field are present. 
Monday, March 2, 2020 11:51AM  12:27PM 
B42.00004: Theory for the unconventional dynamics of ferrimagnets Invited Speaker: Se Kwon Kim Title: Theory for the unconventional dynamics of ferrimagnets 
Monday, March 2, 2020 12:27PM  12:39PM 
B42.00005: Local spin current probe of the global electrodynamics of ultrathin magnetic heterostructure electrofoils David Mayes, Maxwell Grossnickle, Mark I Lohmann, Junxue Li, Vivek Aji, Jing Shi, Justin Song, Nathaniel Gabor Spin current  the flow of angular momentum mediated by electrons  is a unique probe of nontrivial phases in ultrathin magnetic heterostructures. Electron spin, however, is highly sensitive to nearby electric and magnetic fields; thus, it is important to characterize nonlocal effects in spintronic devices. The high spinorbit coupling of platinum in conjunction with ferrimagnetic insulator Yttrium Iron Garnet (YIG) provides an optimal platform for evaluating spin current as a robust probe. Here, we demonstrate the first technique capable of imaging the electric field using spin current as a local probe in Pt/YIG magnetic heterostructures. An imaging laser produces a localized thermal gradient that generates an outofplane spin current. In the Pt layer, this spin current scatters electrons inplane and away from the external magnetic field, producing moving charges which interact with the local electric flux to generate a global voltage that we image in space. Electrofoil Pt/YIG devices, made with airfoilshaped cutouts, are used to study several subtle nonlocal geometric effects, all of which are well described by the ShockleyRamo theorem. 
Monday, March 2, 2020 12:39PM  12:51PM 
B42.00006: On the Field Dependence of SpinLattice Relaxation Johan Van Tol Spin Lattice Relaxation (T_{1}) and spinspin electron spin relaxation processes (T_{2}) are of importance for a variety of applications, like quantum information processing, quantum memory, spin cooling, and dynamic nuclear polarization. We studied the temperature dependence of the relaxation in the high magnetic field regime for a variety of paramagnetic spin systems. High frequency pulsed electron spin resonance at various fields and frequencies in the 314 T range was used to measure directly in the time domain. The lowtemperature direct singlephonon spin lattice relaxation is found to have a strong field dependence (B^{2}B^{4}) in the high frequency/field regime. A comparison is made between transition metal impurities in crystals, donorbound electrons in semiconductors, and other systems of interest to quantum information processing. In spite of their small spinorbit coupling, organic radicals in frozen solutions also show a marked field dependence of T_{1}. This is of importance to dissolution and solid state dynamical nuclear polarization (DNP) for NMR and MRI studies. The experimental results are compared with existing theoretical models. 
Monday, March 2, 2020 12:51PM  1:03PM 
B42.00007: Spin dynamics in the density functional: problems and perspectives Vladimir Antropov We discuss general dynamics in the chargecurrentmagnetization density functional theory. 
Monday, March 2, 2020 1:03PM  1:15PM 
B42.00008: Nonclassical magnetization reversal by quantum spin torque of manyelectron pulse: A timedependent density matrix renormalization group study Marko Petrovic, Petr Plechac, Adrian Feiguin, Branislav Nikolic Using the timedependent density matrix renormalization group (tDMRG) method, we study nonclassical effects in the spintransfer torque (STT) exerted by the spinpolarized electron current on a onedimensional quantum Heisenberg ferromagnetic chain. Unlike standard STT induced dynamics of magnetization viewed as a classical vector of fixed length, quantum STT allows for the establishment of quantum entanglement between spins. Magnetization reversal driven by quantum STT is nonclassical in the sense that no rotation from its initial state occurs. We extend the findings of Ref. [1], which dealt with single electron wave packets impinging onto many quantum spins. In contrast, the tDMRG method allows us to tackle a problem of many quantum electrons coupled to many quantum spins. The quantum local spins, initially oriented along the negative zaxis, undergo a reversal into the positive zaxis direction after interaction with the spinup polarized current. 
Monday, March 2, 2020 1:15PM  1:27PM 
B42.00009: Efficient Method for the Simulation of hightemperature Spin Dynamics Grigorii Starkov, Boris Fine The measurements of nuclear free induction decays (FIDs) can be used to extract microscopic information about solids such as the distances between nuclear spins or electronic spin susceptibility. At the same time, the firstprinciples calculation of solid FIDs, which is important for such an extraction, is a longstanding problem. 
Monday, March 2, 2020 1:27PM  1:39PM 
B42.00010: Physical realization of complex dynamical pattern formation in magnetic spinwave active feedback rings Justin Anderson, Praveen Janantha, Diego Alcala, Mingzhong Wu, Lincoln Carr We report the clean experimental realization of cubicquintic complex GinzburgLandau physics in a single driven, damped system. Five numerically predicted categories of complex dynamical behavior and pattern formation are identified for bright and dark solitary waves propagating around an active magnetic thin film feedback ring: (1) periodic breathing; (2) recurrence; (3) spontaneous spatial shifting; (4) intermittency; and (5) interactions of multiple solitary waves. These nontransient, long lifetime behaviors are observed in microwave spinwave envelopes circulating within a dispersive, nonlinear YttriumIronGarnet wave guide operating in a ring geometry where net losses are directly compensated for via linear amplification on each round trip (~100 ns). The behaviors exhibit periods ranging from 10s to 1000s of round trip times (~ 1 ms) and are stable for 1000s of periods (~1 s). We find these dynamical behaviors span the experimentally accessible ranges of attractive cubic nonlinearity, dispersion, and external field strength that support the selfgeneration of backward volume spinwaves in a fourwave mixing regime. 
Monday, March 2, 2020 1:39PM  1:51PM 
B42.00011: An efficient method of spin dynamics for longrange interacting systems Taichi Hinokihara, Munetaka Sasaki, Seiji Miyashita We developed an efficient method for dynamical simulation, TQMC+SCO, which is useful for classical spin systems with longrange interactions. 
Monday, March 2, 2020 1:51PM  2:03PM 
B42.00012: Mechanism for a chemical potential of nonequilibrium magnons in parametric parallel pumping Naoya Arakawa I present a new theory of parametric parallel pumping for a ferrimagnet and demonstrate a mechanism by which a chemical potential of nonequilibrium magnons is generated [1]. In the parametric parallel pumping, two magnetic fields parallel to each other are used; one is static, and the other is timeperiodic. By using this pumping, we can achieve a nonequilibrium state in which the magnon distribution function is approximated by the Bose distribution function with a finite chemical potential. However, its mechanism has been unclear. In this talk, I will discuss how nonequilibrium magnons in the parametric parallel pumping acquire a finite chemical potential [1]. 
Monday, March 2, 2020 2:03PM  2:15PM 
B42.00013: Generalized magnetoelectronic circuit theory and spin memory loss Alexey Kovalev, Giovanni Baez Flores, Kirill Belashchenko, Mark Schilfgaarde Spin transport at metallic interfaces is an essential ingredient of various spintronic device concepts, such as giant magnetoresistance, spintransfer torque, spinorbit torque, spin Hall magnetoresistance, and spin pumping. Spinorbit coupling plays an important role in many such devices. In particular, spin current is partially absorbed at the interface due to spinorbit coupling. Here, we develop a general magnetoelectronic circuit theory and generalize the concept of spin mixing conductance accounting for various mechanisms responsible for spinflip scattering . For the case when exchange interactions dominate, we give a simple expressions for the spin mixing conductance in terms of contributions responsible for spin memory loss, spin torque, and spin precession, where all contributions are amenable to ab initio treatment. We observe that in general there is no straightforward relation between the spin torque part and the spin memory loss part, where the latter is often expressed in terms of the spin loss parameter, δ. 
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