Sn

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].

In this presentation, we will mainly talk about the magneto-optical properties of Mn₃Sn [5]. We found that despite a vanishingly small magnetization (~2 mμ_B/Mn), Mn₃Sn exhibits a large zero-field MOKE (~20 mdeg), comparable to that in ferromagnetic metals. Our first-principles calculation has clarified that the ferroic ordering of cluster magnetic octupoles in the AF state causes the MOKE even in its fully compensated AF state. This large MOKE further allows imaging of the octupole domains, which are 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 the further development of spintronics devices using AF materials.

[1] T. Jungwirth et al., Nat. Nanotech. 5, 231 (2016).
[2] S. Nakatsuji, N. Kiyohara, and T. Higo, Nature 527, 212 (2015).
[3] M. Ikhlas, T. Tomita et al., Nat. Phys. 13, 1085 (2017).
[4] K. Kuroda and T. Tomita et al., Nat. Mater. 16, 1090 (2017).
[5] T. Higo et al., Nat. Photon. 12, 73 (2018).
[6] T. Higo et al., APL 113, 202402 (2018).