Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session M42: Spin Transport and Magnetization Dynamics in Ferrimagnets and AntiferromagnetsFocus
|
Hide Abstracts |
Sponsoring Units: GMAG Chair: Himanshu Fulara Room: 709/711 |
Wednesday, March 4, 2020 11:15AM - 11:27AM |
M42.00001: Decoherence of transverse spin currents in ferrimagnetic CoGd Youngmin Lim, Behrouz Khodadadi, Jie-Fang Li, Dwight D Viehland, Satoru Emori It has been predicted that the coherence length λc of transverse spin current in antiferromagnetic and ferrimagnetic metals can be much longer than λc ≈ 1 nm in ferromagnets. A recent experiment reports λc > 10 nm in ferrimagnetic CoTb alloys [1], although this is rather surprising given the strong spin-orbit coupling in CoTb. Here, we determine λc in ferrimagnetic Co1-xGdx alloys with much weaker spin-orbit coupling than CoTb. We perform spin pumping measurements on NiFe/Cu/CoGd trilayers, where a coherent spin current pumped from NiFe decoheres in the CoGd spin sink. The spin sink thickness dependence of Gilbert damping enhancement of the NiFe layer allows us to quantify λc. We demonstrate a maximum of λc ≈ 4 nm for the composition of CoGd close to magnetic compensation, indicating partial enhancement of spin coherence due to compensated antiferromagnetic order. We also observe a monotonically decreasing effective spin-mixing conductance with increasing Gd content, suggesting the dominance of Co 3d bands in spin current transport across the interface of the ferrimagnet. |
Wednesday, March 4, 2020 11:27AM - 11:39AM |
M42.00002: Thermal Hall effect, spin Nernst effect, and spin density induced by thermal gradient in collinear ferrimagnets from magnon-phonon interaction Sungjoon Park, Naoto Nagaosa, Bohm-Jung Yang We study the thermal Hall and spin Nernst effect in collinear ferrimagnets on a honeycomb lattice with broken inversion symmetry between the nearest neighbors. The broken inversion symmetry allows nearest-neighbor inplane Dzyaloshinskii-Moriya interaction, which has no effect in the linear spin wave theory. However, it induces large Berry curvature in the magnetoelastic excitation spectrum through the magnon-phonon interaction (MPI) to produce spin-polarized thermal Hall current, so that both spin Nernst and thermal Hall currents are produced. Because the MPI does not conserve the spin, we also compute the boundary spin accumulation. Surprisingly, we do not find any asymmetric boundary spin accumulation, which we attribute to spin nonconservation. However, the MPI induces non-vanishing total spin expectation value in the system with armchair edges. |
Wednesday, March 4, 2020 11:39AM - 11:51AM |
M42.00003: Electric-Field Control of Strain-Driven Tuning of FMR in the Low-Loss Ferrimagnetic Coordination Compound V[TCNE]x Seth Kurfman, Andrew Franson, Piyush Shah, Gopalan Srinivasan, Michael Page, Ezekiel Johnston-Halperin Electric-field control of magnetic resonance has application potential in the design of low-power, compact, high-frequency magnetoelectronic devices, such as microwave filters and circulators. To date, this work has exploited low-loss ferrite materials mechanically coupled to piezoelectric substrates. However, traditional ferrites typically require lattice-matched substrates and extreme growth conditions to produce high-quality material, making on-chip integration while maintaining low damping a significant challenge. Here, we demonstrate electric-field control of the FMR properties of the low-loss (α = (3.98 ± 0.22) × 10-5), organic-based, room-temperature ferrimagnet vanadium tetracyanoethylene (V[TCNE]x≈2) in V[TCNE]x/piezoelectric composite heterostructures. These structures show shifts in the resonant frequency position by ~50 MHz, or more than six times the resonant linewidth. These results demonstrate the potential of V[TCNE]x to complement traditional ferrites in electrically-controlled magnetoelectronic devices. For example, since V[TCNE]x can be deposited on a variety of inorganic substrates, it has the potential to be directly integrated into magnetoelectric devices without the need for flip-chip fabrication techniques. |
Wednesday, March 4, 2020 11:51AM - 12:03PM |
M42.00004: Non-local spin transport measurement in TbIG thin films grown by pulsed laser deposition Wei Yuan, Junxue Li, Victor Ortiz, Yawen Liu, Jing Shi Ferrimagnetic insulators (FMIs) attract a lot of attention in spintronics recently. As a medium, FMIs support pure spin current carried by magnon transport over a relatively long distance. In this work, we use nonlocal method to probe spin transport in terbium iron garnet (Tb3Fe5O12 or TbIG). We obtain high-quality epitaxial TbIG thin films on the substrates of GGG(111) using a PLD system. After 750 degree Celsius post-growth rapid thermal annealing, clear RHEED patterns demonstrate the single crystal quality of TbIG films, which is further confirmed by X-ray diffraction and atomic force microscopy results. The non-local signal has a sign reversal at 270 K, which corresponds to the compensation temperature of TbIG. Below the compensation temperature, the non-local signal stays approximately constant until a dramatic increase sets in at 50 K, which persists to the lowest temperature of 2 K. We attribute this rapid increase to the spin current transport associated with paramagnetic Tb-spins. We also discuss the temperature dependence of the nonlocal signal in garnets with and without rare-earth moments. |
Wednesday, March 4, 2020 12:03PM - 12:15PM |
M42.00005: Anomalous spin Hall angle of a metallic ferromagnet determined by a multiterminal spin injection/detection device Tobias Wimmer, Birte Coester, Stephan Geprägs, Rudolf O Gross, Sebastian T. B. Goennenwein, Hans Huebl, Matthias K Althammer We report on the determination of the anomalous spin Hall angle in the ferromagnetic metal alloy cobalt-iron (Co25Fe75, CoFe). This is accomplished by measuring the spin injection/detection efficiency in a multiterminal device with nanowires of platinum (Pt) and CoFe deposited onto the magnetic insulator yttrium iron garnet (Y3Fe5O12, YIG). Applying a spin-resistor model to our multiterminal spin transport data, we determine the magnon conductivity in YIG, the spin conductance at the YIG/CoFe interface and finally the anomalous spin Hall angle of CoFe as a function of its spin diffusion length in a single device. Our experiments clearly reveal a negative anomalous spin Hall angle of the ferromagnetic metal CoFe, but a vanishing ordinary spin Hall angle. This work therefore adds new observations to the results reported in Refs. [1,2], where the authors found finite contributions of the ordinary spin Hall angle in the ferromagnetic metals Co and permalloy. |
Wednesday, March 4, 2020 12:15PM - 12:27PM |
M42.00006: Investigation of nonequilibrium processes of magnetoelastic waves and evidence of their BEC formation in an antiferromagnetic system Vladimir L Safonov, Derek Bas, Yuri V Rostovtsev, James A Roberts, Diana Berman, Michael E McConney, Michael Page The canted antiferromagnet FeBO3 exhibits strong nonlinear interactions between magnetoelastic waves that can manifest as a variety of interesting phenomena. We show that excited magnetoelastic waves and their quanta, which we refer to as mexons, exhibit a wide range of nonequilibrium nonlinear wave phenomena including mode competition under noisy pumping, full submission to external coherent fields, and evidence of quasi-equilibrium Bose-Einstein condensation (BEC) at room temperature. The mode we suggest as the mexon BEC exhibits extremely high efficiency with a quality factor of Q ~ 8x105. Remarkably, this behavior occurs in a system that is very near its transition temperature due to the heat generated by microwave pumping. Our results suggest that such systems can be of technological importance due to the uniqueness of the mode quality and ability to modulate external signals, as well as from the standpoint of studying a whole class of nonlinear wave phenomena usually taking place in a wide range of environments and conditions. |
Wednesday, March 4, 2020 12:27PM - 12:39PM |
M42.00007: Elimination of two-magnon scattering for evaluation of intrinsic spin decay length in antiferromagnetic insulator Hiroto Sakimura, Takashi Harumoto, Yoshio Nakamura, Ji Shi, Kazuya Ando We present an experimental evaluation of the intrinsic spin decay length in an antiferromagnetic insulator (AFI). A frequently-used sample configuration to study the spin-current propagation in AFIs is a ferromagnet/AFI/heavy-metal trilayer structures, where the ferromagnet and heavy-metal act as spin-current injectors and detectors, respectively. We found that at the ferromagnet/AFI interface, a spin current generated by spin pumping is strongly suppressed by two-magnon scattering enhanced by position-dependent fluctuation of microscopic exchange bias, which is inevitable at ferromagnet/antiferromagnet junctions. By eliminating the two-magnon contribution from the spin transmission signal, we discovered that the characteristic length of spin decay in polycrystalline NiO, a prototypical AFI, was around 100 nm, which is an order of magnitude longer than what was previously believed. Our results provide a new perspective in the emerging field of antiferromagnetic spintronics, especially for the fundamental understanding of spin transport physics in insulators. |
Wednesday, March 4, 2020 12:39PM - 12:51PM |
M42.00008: Nuclear spin Seebeck effect in antiferromagnets Derek Reitz, Yaroslav Tserkovnyak The spin Seebeck effect (SSE) involves transfer of spin angular momentum between a magnet and a metal from internal thermal fluctuations. SSE is usually dominated by electronic, rather than nuclear, spins, since interfacial exchange is much stronger than interfacial hyperfine coupling. At low temperatures, however, electronic magnon thermal occupation numbers are exponentially suppressed, while nuclear spins remain active. The nuclear spins are paramagnetic, weakly polarized in the large hyperfine field of the Neel order. One source for nuclear SSE is interfacial nuclear, metal spin flip-flops, known as Korringa relaxation. Nuclear SSE is then determined by competing rates: thermalization with phonons via hyperfine coupling to electrons in the magnet, and Korringa relaxation into the metal. |
Wednesday, March 4, 2020 12:51PM - 1:03PM |
M42.00009: Topological Hall effect in canted antiferromagnets Jotaro Nakane, Kazuki Nakazawa, Hiroshi Kohno The topological Hall effect (THE) is a Hall effect caused by a noncoplanar spin texture, or its spin chirality, in ferromagnetic conductors. This effect is absent in antiferromagnets (AF) due to the cancellation of the two sublattice chiralities. However, if the AF spins are canted, the overall spin chirality, hence the THE, can be finite. |
Wednesday, March 4, 2020 1:03PM - 1:39PM |
M42.00010: Magnetization dynamics and spin transport in compensated ferrimagnets Invited Speaker: Kyung-Jin Lee Spintronics is a multidisciplinary field whose central theme is the active manipulation of electron spins in solid-state systems. The core magnetic system for spintronics research has been ferromagnets since they serve as spin-polarizers/detectors and offer non-volatile memory and logic technologies. Recently, much effort has been expended in employing antiferromagnetic coupled systems as core elements because of their fast dynamics and efficient spin-torque generation. We will discuss the underlying mechanism of fast dynamics of compensated and uncompensated staggered spin moments, driven by magnetic fields or spin torques [1-3]. We will also discuss the increased efficiency of spin torques due the weakened spin dephasing in compensated ferrimagnets [4,5]. |
Wednesday, March 4, 2020 1:39PM - 1:51PM |
M42.00011: Thermal spin-Edelstein effect in an antiferromagnetic insulator/normal metal heterostructure Hantao Zhang, Ran Cheng In an antiferromagnetic insulator with biaxial anisotropy and the Dzyaloshinskii-Moriya interaction (DMI), symmetry ensures a spin-momentum locking similar to that of gapped Rashba electrons. A temperature gradient can generate an interfacial magnon accumulation with a preferred spin polarization, realizing the magnonic counterpart of the spin Edelstein effect. This thermally-driven magnonic spin accumulation can be injected into an adjacent heavy metal and converted into a measurable voltage, which depends monotonically on both temperature and DMI but non-monotonically on the surface-induced magnetic anisotropy. It is found that the overall response coefficient has to be solved under a nontrivial boundary condition regarding spin transmission across the interface. |
Wednesday, March 4, 2020 1:51PM - 2:03PM |
M42.00012: Strain-Tunable Magnetic Anisotropy in Sputtered Thulium Iron Garnet (TIG) Thin Films and TIG/Au/TIG Trilayers Gilvania Da Silva Vilela, HANG CHI, Gregory Stephen, Charles Settens, Preston Zhou, Yunbo Ou, Dhavala Suri, Don Heiman, Jagadeesh Moodera Ferromagnetic insulator thin films have been explored for developing spintronic devices. When combined with quantum materials, the strongly correlated interaction from the proximitized interface results in intense local magnetic fields which modulates them to displaying new interface physical phenomena. We investigate ways to tune the magnetic anisotropy in TIG films by selecting their thickness, substrate, and annealing conditions. When deposited over (111) GGG, they present a negative magnetostriction constant which favors a perpendicular magnetic anisotropy (PMA). While PMA allows high magnetic storage density in hard disk drives, it is required for breaking the time-reversal symmetry in topological insulators (TIs) to aim towards quantized anomalous Hall state in TIs. Controlling the film preparation parameters we observed that TIG films under compressive strain display an in-plane magnetic anisotropy, whereas films under tensile strain demonstrated PMA. These results led to the successful fabrication of TIG/Au/TIG magnon valve structures with independent magnetic switching of each TIG layer. |
Wednesday, March 4, 2020 2:03PM - 2:15PM |
M42.00013: Quantum Dynamics of Matrix Product States on Transformed bases Amir Mohammadaghaei, Kirill Shtengel Numerical simulation of the quantum states under the unitary evolution with generic non-integrable Hamiltonians still remains a challenge. The exact diagonaliztion (ED) method only works for very small system sizes and methods based on matrix product states (MPS), such as time dependent variational principle (TDVP) fail to capture long time behavior of the systems, such as the diffusion constant, with controlled precision. The main culprit is believed to be the rapid entanglement growth to volume-law in real space cuts. The entanglement blow-up makes the long-times inaccessible for variational ansatz that are designed to represent states with area-law entanglement entropy. In this work, we explore a MPS time evolution but on a set of transformed bases that are local both in real and fourier space. We benchmark this method on the anti-ferromagnetic Heisenberg chain with longer range exchange terms to bring the system our of integrability. We demonstrate the possibility of achieving longer time simulations by comparing the results to exact ED as well as TDVP on real space. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700