Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session UU02: V: Magnetization and Spin Dynamics |
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Sponsoring Units: GMAG Chair: Qingming Zhang, Lanzhou University/Institute of Physics Room: Virtual Room 2 |
Wednesday, March 22, 2023 5:00AM - 5:12AM |
UU02.00001: Long-range order coexisting with long-range entanglement: Is Nd2Sn2O7 the first Coulombic antiferromagnet with a visible emergent gauge photon? Gang Chen Exotic state of matter could coexist with conventional orders such that the gauge fields and fractionalized excitations could prevail in a seemingly ordered state. By digging out and examining old experiments, we identify the pyrochlore Nd2Sn2O7 as a Coulombic antiferromagnet. This novel and exotic state carries both antiferromagnetic order and emergent quantum electrodynamics with gapless gauge photon and fractionalized quasiparticles. The antiferromagnetic order and the gauge photon naturally explain the neutron diffraction result and the anomalously large T 3 specific heat, respectively. We propose the representative dynamical properties for the Coulombic antiferromagnet that can be examined by the inelastic neutron scattering measurements. If the experiment in Nd2Sn2O7 can be repeated, Nd2Sn2O7 might become the first Coulombic antiferromagnet with a visible emergent gauge photon and thus an unique system with both the long-range order and the long-range entanglement. We also expect this work to inspire interests in the search of exotic physics in ordered magnets. |
Wednesday, March 22, 2023 5:12AM - 5:24AM |
UU02.00002: Spin dynamics of Heisenberg spin-1/2 chain in incommensurate field Jiahao Yang, Jianda Wu Based on Bethe ansatz, we develop a non-perturbative analytical method to study the Heisenberg spin-1/2 chain in incommensurate (IC) field. The obtained dynamical spectra exhibit a series of zero-energy peaks which can be attributed to the scattering between Bethe states connected by the IC field. With IC field tuning, a gap gradually develops in the dynamical spectrum of Bethe strings and psinon-antipsinon pairs. Our results reveal a novel behavior of those quasiparticles under the IC field tuning, and the non-perturbative approach also allows us to analytically investigate physics beyond integrability. |
Wednesday, March 22, 2023 5:24AM - 5:36AM |
UU02.00003: Dynamics and reversible control of the vortex Bloch point domain wall in short cylindrical magnetic nanowires Farkhad G Aliev, DIEGO CASO PARAJON, Kostantin Guslienko, Pablo Tuero, Javier García Low dissipation switching of nanomagnets is one of the main challenges in the development of future magnetic memories. We numerically investigate the evolution of the static and dynamic spin wave (SW) magnetization in short (50-400 nm length and 120 nm diameter) cylindrical ferromagnetic nanowires, where competing single vortex (SV) and vortex domain wall with a Bloch point (BP-DW) magnetization configurations could be formed. For a limited length range (between 150 and 300 nm) we demonstrate a reversible microwave field induced (forward) and opposite spin currents (backwards) transitions between the topologically different SV and BP states. By tuning the nanowire length, excitation frequency, the microwave pulse duration and the spin current values we show that the optimum (low power) manipulation of the BP-DW could be reached by a microwave excitation tuned to the main SW mode and for nanowire lengths around 230-250 nm, where single vortex domain wall magnetization reversal via nucleation and propagation of SV-DW takes place. An analytical model for dynamics of the Bloch point provides an estimation of the gyrotropic mode frequency close the one obtained via micromagnetic simulations. Our findings open a new pathway for the creation of unforeseen topological magnetic memories. |
Wednesday, March 22, 2023 5:36AM - 5:48AM |
UU02.00004: Magneto-structural transition in MnCoGe thin films investigated by ferromagnetic resonance Voicu O Dolocan, Elie Assaf, Loic Patout, Ahmed Charai, Khalid Hoummada, Maxime Bertoglio, Sylvain Bertaina We investigated the relation between magnetic and structural properties of magnetocaloric MnCoGe thin films grown on different substrates. The thin films show a hexagonal structure at room temperature with polycristalline form when grown on Si substrates or a highly textured columnar grains with same orientation when grown on Ge substrates. Their static and dynamic magnetic properties show anomalies at lower temperature, consistent with a gradual mixing of hexagonal and orthorhombic structures. Below a blocking temperature, the thin films show glassy behavior and a decoherence of the FMR mode in the normal direction down to 10K. We relate our experimental results to the the martensitic strain in the sample, due to the hexagonal to orthorhombic structural transition, which affects the magnetocrystalline anisotropy and is known to be sensitive to the morphology (grain size and grain boundaries). We show that the dynamic magnetic properties are strongly dependent on morphology, as the decoherence of the normal FMR mode does not apear for polycrystalline MnCoGe films grown on Si substrates, even though a similar behavior is observed below 10K. Our results suggest a dynamic magnetic ground state in mcg thin films at low temperature. |
Wednesday, March 22, 2023 5:48AM - 6:00AM |
UU02.00005: Voltage-Controlled High-Bandwidth Terahertz Oscillators Based On Antiferromagnets Kjetil Magne D Hals, Mike A Lund, Karin Everschor-Sitte, Davi R Rodrigues The terahertz (THz) technology gap refers to a frequency range of electromagnetic radiation in the THz regime where current technologies are inefficient for generating and detecting radiation. Here, we show that noncollinear antiferromagnets (NCAFM) with kagome structure host gapless self-oscillations whose frequencies are tunable from 0 Hz to the THz regime via electrically induced spin-orbit torques (SOTs). The auto-oscillations' initiation, bandwidth, and amplitude are investigated by deriving an effective theory, which captures the reactive and dissipative SOTs. We find that the dynamics strongly depends on the ground state's chirality, with one chirality having gapped excitations, whereas the opposite chirality provides gapless self-oscillations. Our results demonstrate that NCAFMs offer unique THz functional components, which could play a significant role in bridging the gap between technologies operating in the microwave and infrared regions. |
Wednesday, March 22, 2023 6:00AM - 6:12AM |
UU02.00006: Perturbation Approach for Nuclear Magnetic Resonance with a General Periodic Transverse Field Sunghyun Kim, ZHICHEN LIU, Richard A Klemm Quantum mechanically, when a nucleus of magnetic moment mN and spin I interacts with a constant magnetic field H0 in the z direction and with a weaker time t-dependent field H1cos(wt) in the x direction, the standard Hamiltonian H for nuclear magnetic resonance is H = Izw0+Ixw1cos(wt), where w0= mNH0 and w1= mNH1. More generally, the time-dependent field can have a more general periodic time dependence, so that the most general nuclear magnetic resonance Hamiltonian may be written as H = Izw0+Ixw1f(t), where f(t) is a general periodic function of the time t with period 2p/w, which can be represented by a Fourier series expansion. Although, to our knowledge, this problem has not yet been solved exactly, we solved this problem using time-dependent perturbation theory in the interaction picture to third order in perturbation theory. Although the expression for the amplitude of a transition from the most general initial state, a linear combination of the 2I+1 quantum states |I,m> , to the final state is complicated, some numerical results valid to this order will be presented. Such results should prove useful for experimental analyses. |
Wednesday, March 22, 2023 6:12AM - 6:24AM |
UU02.00007: Rotating Wave Approximation to Nuclear Magnetic Resonance for Arbitrary Spins ZHICHEN LIU, Sunghyun Kim, Richard A Klemm
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Wednesday, March 22, 2023 6:24AM - 6:36AM |
UU02.00008: Ab Initio study of the Co and Ni complexes, vacancies, and pairs in ZnS Cuneyt Sahin Transitional metal impurities in wide band-gap semiconductors are excellent platforms to study doped materials' magnetic properties for optoelectronics, quantum information, and spintronic applications. This study focuses on cobalt (Co) and nickel (Ni) substitutional impurities in zinc-sulfide (ZnS). We first calculate the electronic structures and density of states for substitutional Co and Ni, as well as Co-vacancy, Ni-vacancy, Co-Co pairs, Ni-Ni pairs, and Co-Ni pairs. We also compute the formation energies in different charged states. For the transition metal pairs, we also compute the exchange energy between the ferromagnetic and antiferromagnetic configurations and report the dependence of this energy on the pair separation in the ZnS host. Finally, we add the Hubbard U corrections and report the change in the FM-AFM ground state as a function of the strength of the U parameter. |
Wednesday, March 22, 2023 6:36AM - 6:48AM |
UU02.00009: Ultrafast perturbation of magnetic domains by optical pumping in a ferromagnetic multilayer Thomas J Silva I will present pump-probe experimental results that clearly demonstrate the ultrafast modification of magnetic domains and domain walls after optical pumping in a sample supporting a labyrinth domain pattern (1). The sample is a 40 nm Co/Ni multilayer. The experiments were conducted at the LCLS free electron laser. Domain alteration was measured by ultrafast magnetic X-ray scattering. 3 concentric diffraction rings were seen; the first 3 Fourier intensities of the domain pattern. The initial domain wall width is 39 nm from Fourier analysis of the ring intensities. The ring radii correspond to a domain width of 80 nm. After pumping, the three rings partly quenched, with almost 100% quenching for the highest order ring, while the first order ring quench by less than 50%. Our analysis determined that the domain walls broaden by 12 nm in <1.2 ps. We also found that the 1stand 3rd order rings broaden and shift to lower scattering vector. The quantitative measurement of the wall broadening proves the ring shift is not from wall broadening, contrary to the assertion of Pfau, et al. (2). Ring broadening implies a reduction in the domain correlation length from 845 nm to 712 nm, requiring wall speeds >2km/s. The ring radii contraction is consistent with an ultrafast increase in the average domain size. New measurements at Eu-XFEL confirm ring broadening and radius shift, but only for labyrinths, not stripes (3). |
Wednesday, March 22, 2023 6:48AM - 7:00AM |
UU02.00010: Angular dependence of the electrically-driven and -detected ferromagnetic resonance Qiang Gao, Maxim Tsoi Electrically driven/detected ferromagnetic resonance (FMR) is a powerful technique for studying spin dynamics in magnetic materials and heterostructures. Here the magnetic moment of the specimen precesses about the direction of the static magnetic field and energy is absorbed strongly from the FMR-driving microwave current in the specimen when its frequency is equal to the precessional frequency. In this work we study the dependence of FMR on the relative orientation between the static magnetic field and the driving microwave current. The angular dependence of FMR in a Ni34Fe66 wire was measured for the magnetic field applied at an angle θ with respect to the wire and the driving current flowing along the wire. Both traditional microwave-absorption and electrical detection techniques show very similar behaviors with the resonance magnetic field following a simple “1/cos(θ)" dependence. Our findings emphasize the importance of the driving current direction in FMR experiments. |
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