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 B35: Topological Spintronics using Chiral AntiferromagnetsInvited Live
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Sponsoring Units: GMAG Chair: Collin Broholm, Johns Hopkins University |
Monday, March 15, 2021 11:30AM - 12:06PM Live |
B35.00001: Large magneto-optical effects in the topological chiral antiferromagnet Mn3Sn Invited Speaker: Tomoya Higo There has been a surge of interest in antiferromagnetic (AF) materials due to their favorable properties for device applications, including a vanishingly small stray field and faster (THz) spin dynamics compared to ferromagnets. In fact, motivated by these intriguing properties, several breakthroughs have been made: an anisotropic magnetoresistance (even-function response under time-reversal (TR)) for detecting collinear AF ordering [1]. Another breakthrough is an odd-function response under TR in the chiral antiferromagnet Mn3Sn, such as an anomalous Hall and Nernst effects at zero magnetic field [2,3]. Moreover, recent studies have revealed that Mn3Sn is a TR symmetry breaking Weyl metal possessing a large and controllable Berry curvature in momentum space [4]. |
Monday, March 15, 2021 12:06PM - 12:42PM Live |
B35.00002: New aspects of magnetoelectric responses in chiral antiferromagnets Invited Speaker: Hua Chen Antiferromagnets have always been overshadowed by ferromagnets in real-life applications based on magnetism or spintronics. This is primarily due to that antiferromagnet order parameters, in contrast to the ferromagnetic magnetization, are only weakly coupled to magnetic fields, and are hence difficult, in conventional view, to be manipulated. I will discuss several recent theoretical and experimental developments that counter this conventional wisdom, in a class of antiferromagnets that have stable noncollinear magnetic order. I will first explain a theory for the time-reversal-symmetry-breaking counterparts of the conventional SHE and ISHE in the noncollinear antiferromagnet Mn3Sn, which are named as the magnetic spin Hall effect (MSHE) and the magnetic inverse spin Hall effect (MISHE), respectively [1]. I will then discuss the concept of spin density polarization, and how to use it to describe spin-Hall effects in a magnetic insulator as bulk effects, without using the spin current language [2]. I will finally present an exploration on the nontrivial orbital coupling between chiral antiferromagnets and external magnetic fields [3,4], and the potential detection of the elusive itinerant orbital magnetization by magnetic neutron scattering. |
Monday, March 15, 2021 12:42PM - 1:18PM Live |
B35.00003: Physics of domains and domain walls in topological magnets Invited Speaker: Leon Balents We will discuss the energetics and dynamics of domains and the boundaries between them in two examples of topological magnets: antiferromagnetic Weyl metals, as exemplified by Mn3Sn, and quantum anomalous Hall states as is observed in twisted bilayer graphene. The two cases will be distinctly contrasted and compared, and implications for experiments outlined. |
Monday, March 15, 2021 1:18PM - 1:54PM Live |
B35.00004: Anti-chiral spin order, its soft modes, and their hybridization with phonons in the topological semimetal Mn3Ge. Invited Speaker: Jonathan Gaudet We report the magnetic structure and spin excitations of Mn3Ge, a breathing kagome antiferromagnet with transport anomalies attributed to Weyl nodes. Using polarized neutron diffraction, we show the magnetic order is a k = 0 co-planar state belonging to a Γ9 irreducible representation, which can be described as a perfect 120° anti-chiral structure with a moment of 2.2(1)μB/Mn, superimposed with weak collinear ferromagnetism. Inelastic neutron scattering shows three collective Q = 0 excitations at Δ1= 2.9(6) meV, Δ2 = 14.6(3), and Δ3 = 17.5(3) meV. A field theory of Q ≈ 0 spin waves in triangular antiferromagnets with a 120° spin structure was used to classify these modes. The in-plane mode (α) is gapless, Δ1 is the gap to a doublet of out-of-plane spin excitations (βx,βy), and Δ2, Δ3 result from hybridization of optical phonons with magnetic excitations. While a phenomenological spin Hamiltonian including exchange interactions, Dzyaloshinskii-Moriyainteractions, and single ion crystal field terms can describe aspects of the Mn-based magnetism, spin wave damping (Γ = 25(8) meV) and the extended range of magnetic interactions indicate itinerant magnetism consistent with the transport anomalies. |
Monday, March 15, 2021 1:54PM - 2:30PM Live |
B35.00005: The Functionality of a Topological Chiral Antiferromagnet Mn3X (X=Sn, Ge) Invited Speaker: Yoshichika Otani Chiral antiferromagnets Mn3X (X=Sn and Ge) exhibit large magnetoelectric, thermoelectric, and optical responses such as anomalous Hall effect (AHE), anomalous Nernst effect (ANE), and magneto-optical Kerr effect (MOKE); their magnitudes reach almost the same as those of ferromagnetic metals. All of these characteristic properties of Mn3X imply that the spin Hall effect (SHE) could also occur. Our recent study demonstrated that a novel type of contribution to the SHE (magnetic SHE, MSHE) and the inverse SHE (MISHE) absent in nonmagnetic materials could be dominant in the antiferromagnets, Mn3X. We attribute this dominant magnetic mechanism to the momentum-dependent spin splitting produced by the noncollinear magnetic order,i.e., the cluster magnetic octupole (CMOP), comprising two sets of three spin sublattices. Moreover, the cluster magnetic octupole takes ferroic order on the Kagome lattice, macroscopically breaking the time-reversal symmetry. Previous studies also revealed that the cluster magnetic octupole, not the magnetic dipole, plays an essential role as the magnetic order parameter for antiferromagnetic domains and domain walls. |
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