Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session A29: Nonlocal magnon spin transport: new concepts and materialsInvited Live Streamed
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Sponsoring Units: GMAG DMP Chair: Timo Kuschel, Universität Bielefeld Room: McCormick Place W-190B |
Monday, March 14, 2022 8:00AM - 8:36AM |
A29.00001: Nonlocal detection of out-of-plane magnetization in a magnetic insulator by thermal spin drag Invited Speaker: Can Avci Recent demonstrations of efficient current-induced control of magnetization in magnetic insulators (MIs), combined with their highly tunable properties, provide fertile grounds for spintronic research and applications [1]. Despite MIs’ electrically insulating nature, the various spin transport phenomena (spin Seebeck, spin Hall, etc.) have granted us the relevant tools to detect their magnetization vector in a local geometry with simple electrical measurements [2]. It was later discovered that the MIs' magnetization vector can be detected also in a nonlocal geometry by long-distance magnon transport. However, this method is limited to the in-plane magnetization component and to films allowing long magnon diffusion. A general detection scheme in a nonlocal device geometry for the magnetization vector both in-plane and out-of-plane, and independently of the long-range magnon transport, remained a challenge for a long time. |
Monday, March 14, 2022 8:36AM - 9:12AM |
A29.00002: Isospin of magnons and birefringence-like spin transport in antiferromagnetic insulators Invited Speaker: Ran Cheng Collinear antiferromagnets with uniaxial anisotropy afford spin wave excitations (dubbed magnons) of both right and left handed chirality, forming an internal degree of freedom - magnonic isospin - capable of encoding information and transporting spin angular momenta over long distances without incurring Joule heating. However, it is commonly conceived that biaxial antiferromagnets (with coexisting easy-axis and easy-plane anisotropy) are not able to function as their uniaxial cousins in spin transport because magnons are linearly polarized and do not carry angular momenta due to rotational symmetry breaking. Here we challenge this seemingly established property by reporting experimental evidence that hematite thin film, in which magnons are linearly polarized, can efficiently transmit spins over micrometer distances. Using proper boundary conditions, we extract the spin decay length showing an unconventional temperature dependence which cannot be explained solely by thermal magnon scattering. We interpret our observations as an interference of the two linearly-polarized propagating magnons in analogy to the birefringence effect in optics, which can further be characterized by an effective precession of the isospin. Furthermore, our devices can realize a bi-stable spin-current switch with a 100% on/off ratio under zero remnant magnetic field. These findings open new intriguing arenas for non-volatile and low-field manipulation of spin transport in antiferromagnetic materials. |
Monday, March 14, 2022 9:12AM - 9:48AM |
A29.00003: Observation of magnon pseudospin dynamics and the Hanle effect in antiferromagnetic insulators Invited Speaker: Matthias K Althammer The spin-1/2 of an electron makes it an archetypal two-level system and inspires thedescription of other two-level systems using an analogous pseudospin. The quantized spin excitations of an ordered antiferromagnet can be viewed as pairs of spin-up and -down magnons and can be characterized by a magnonic pseudospin. The similarity between electronic spin and magnonic pseudospin has triggered the prediction of exciting phenomena like emergent spin-orbit coupling and topological states in antiferromagnetic magnonics. In the last year, first experimental observations of the associated dynamics of antiferromagnetic pseudospin have been reported [1,2]. I will summarize these experimental and theoretical findings, introduce our next step to expand the concept of magnon pseudospin and the description of magnon pseudospin dynamics [3,4] and discuss the influence of dimensionality on the magnon Hanle effect. Additionally, I will show our recent experiments demonstrating control of magnon spin transport and pseudospin dynamics in thin films with varying thickness of the antiferromagnetic insulator hematite (α-Fe2O3) utilizing two Pt strips for all-electrical magnon injection and detection [1] . We observe an oscillation in polarity of the magnon spin signal at the detector as a function of the applied magnetic field, which we quantitatively explain in terms of diffusive magnon transport. In particular,we observe a coherent precession of the magnon pseudospin caused by the easy-plane anisotropy and the Dzyaloshinskii-Moriya interaction. Moreover, we find peculiar changes in the magnon spin signal for thicker hematite layers. Our results are paramount in unnlocking the high potential of antiferromagnetic magnonics towards the realization of electronics-inspired phenomena. |
Monday, March 14, 2022 9:48AM - 10:24AM |
A29.00004: Non-local magnon and phonon spin transport Invited Speaker: Rembert A Duine One of the goals of spintronics is to achieve dissipationless spin currents. In this talk, I will discuss magnon and phonon spin transport through magnetic and non-magnetic insulators that is actuated and detected non-locally by electrical means. For magnetic insulators the spin current is, in the simplest case, carried by magnons and has a decay length on the order of several micrometers. For non-magnetic insulators, the spin current is carried by phonons leading to a decay length on the order of millimeters. More exotic forms of spin transport, such as spin superfluidity, are also mentioned. |
Monday, March 14, 2022 10:24AM - 11:00AM |
A29.00005: Quasiparticle spin-to-charge conversion in superconductors detected by nonlocal magnon spin transport Invited Speaker: Kun-Rok Jeon Injection and excitation of electrons, typically called Bogoliubov quasiparticles (QPs), in a superconductor (SC) with either external (Zeeman) or internal (exchange) spin-splitting field under non-equilibrium conditions (i.e. voltage bias or temperature gradient) have been one of the central research topics in superconducting spintronics. This is because their exotic transport properties, derived from the superconductivity-facilitated coupling between different non-equilibrium imbalances (e.g. spin, charge, heat and spin-heat), can considerably improve the functionality and performance of spintronic devices. |
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