Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session D19: Topological Spintronics using Chiral AntiferromagnetsInvited
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Sponsoring Units: GMAG Chair: Collin Broholm, Johns Hopkins University Room: 207 |
Monday, March 2, 2020 2:30PM - 3:06PM |
D19.00001: 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 2, 2020 3:06PM - 3:42PM |
D19.00002: Large magneto-optical Kerr effect in the non-collinear antiferromagnetic metal 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, faster spin dynamics, and more abundance in nature compared to their ferromagnetic counterparts. 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 non-collinear antiferromagnetic metal Mn3Sn such as an anomalous Hall effect (AHE) [2] and anomalous Nernst effect (ANE) [3] at zero magnetic field. 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 2, 2020 3:42PM - 4:18PM |
D19.00003: Magnetic Spin Hall Effect of a Topological Chiral Antiferromagnet Mn3Sn Invited Speaker: Yoshichika Otani A chiral antiferromagnet Mn3Sn exhibits a substantial anomalous Hall effect (AHE) at room temperature, the magnitude of which reaches almost the same order of magnitude as in ferromagnetic metals irrespective of a small spontaneous magnetization of about 1 mT [1]. This large AHE originates from a significantly enhanced Berry curvature associated with the formation of Weyl points near Fermi energy [2]. A detailed comparison between angle-resolved photoemission spectroscopy measurements and density functional theory calculations revealed significant bandwidth renormalization and damping effects due to the strong correlation among Mn 3d electrons. Magnetotransport measurements provide strong evidence for the chiral anomaly of Weyl fermions[3]. All the above characteristic electronic properties of Mn3Sn imply that the spin Hall effect could also take place in the Mn3Sn. |
Monday, March 2, 2020 4:18PM - 4:54PM |
D19.00004: Anti-chiral order and damped spin waves in the topological semi-metal Mn3Ge Invited Speaker: Jonathan Gaudet The kagome hexagonal compound Mn3Ge is a room temperature non-collinear antiferromagnet with anomalous transport properties associated with electronic Weyl nodes near the chemical potential. The coupling of its electronic transports with magnetic order presents important technological opportunities for which, I will describe our experimental efforts to understand the magnetism of Mn3Ge through neutron scattering techniques. Using polarized neutron diffraction, we show the magnetic order is a k=0 co-planar anti-chiral state with weak ferromagnetism described by a Γ9 irreducible representation with magnetization remarkably aligned perpendicular to an applied field. Using time-of-flight neutron spectroscopy, we find three collective excitations above distinct Γ-point anisotropy gaps. These can be modeled as the normal modes of an anti-chiral triangular spin plaquette where an out-of-plane mode anti-crosses an optical phonon near 15-18 meV. Away from the zone center, magnetic excitations form a broad maximum near 75 meV with a half-width at half maximum of 25(5) meV indicative of itinerant magnetism. We develop a field theory of spin waves, which accurately describes the long wavelength magnetic properties, and use it to determine an effective low energy spin hamitonian for Mn3Ge. |
Monday, March 2, 2020 4:54PM - 5:30PM |
D19.00005: New aspects of magnetoelectric responses in chiral antiferromagnets Invited Speaker: Hua Chen Despite the significant academic interest in them and their richness in nature, antiferromagnets have always been overshadowed by ferromagnets in real-life applications based on magnetism or spintronics. This is primarily due to the fact 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. In this talk I will discuss a number of 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 recent experimental discovery of time-reversal-symmetry-breaking counterparts of the conventional SHE and ISHE in the noncollinear antiferromagnet Mn3Sn, which we name as the magnetic spin Hall effect (MSHE) and the magnetic inverse spin Hall effect (MISHE), respectively. Then I will 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. The talk will end with an exploration on the nontrivial orbital coupling between chiral antiferromagnets and external magnetic fields. |
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