Large magneto-optical effects in the topological chiral antiferromagnet Mn₃Sn

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].

In this presentation, we will mainly talk about the magneto-optical properties of Mn₃Sn [5]. We found that despite a negligibly small magnetization, Mn₃Sn exhibits a large zero-field MOKE (~20 mdeg), comparable to that in ferromagnets. Our first-principles calculation has clarified that the ferroic ordering of cluster magnetic octupoles causes the MOKE even in its fully compensated AF state. This large MOKE further allows imaging of the octupole domains, strongly related to other TR-odd responses induced by the Berry curvature. We will also show that Mn₃Sn thin films exhibit the large time-reversal-odd response as well as the bulk Mn₃Sn [6]. These findings provide an important step for further developing optical and/or spintronics studies using AF materials [7,8].

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[4] Kuroda⁺, Tomita⁺ et al., Nat. Mater. 16, 1090 (2017).
[5] Higo et al., Nat. Photon. 12, 73 (2018).
[6] Higo et al., APL 113, 202402 (2018).
[7] Matsuda et al., Nat. Commun. 11, 909 (2020).
[8] Tsai⁺, Higo⁺ et al., Nature 580, 680 (2020).