Electrical manipulation and ultrafast dynamics of cluster magnetic octupole in the chiral antiferromagnet Mn₃Sn

A magnetic Weyl semimetal is a recent focus of extensive research as it may exhibit large and robust transport phenomena associated with topologically protected Weyl points in momentum space. Mn₃Sn is an example of an antiferromagnetic Weyl semimetal that exhibits a large response comparable to the one observed in ferromagnets despite a vanishingly small magnetization [1]. The noncollinear spin order in Mn₃Sn can be viewed as a ferroic order of cluster magnetic octupole and breaks the time-reversal symmetry, stabilizing Weyl points and the significantly enhanced Berry curvature near the Fermi energy. Thus, manipulation and understanding of the octupole dynamics form the basis for future control of the antiferromagnetic Weyl semimetal.

In this talk, we show how the cluster magnetic octupole in Mn₃Sn is electrically manipulated by the spin-orbit torque [2] and how the dynamics of the octupole is probed by time-resolved magneto-optical Kerr effect [3] and x-ray magnetic circular dichroism [4]. Specifically, we show the giant effective damping of the octupole dynamics, which guarantees the potential of an ultrafast switching at <10 ps, a hundred times faster than the case of spin-magnetization in a ferromagnet. This work paves the path toward realizing ultrafast spintronic devices using the antiferromagnetic Weyl semimetal.

This work was done in collaboration with S. Sakamoto, H. Kosaki, M. Shiga, T. Higo, H. Tsai, T. Nomoto, T. Tomita, M. Ikhlas, A. Sakai, A. Kobayashi, Y. Otani, R. Arita, and S. Nakatsuji of the University of Tokyo, K. Kondou of RIKEN, S. Iihama, and S. Mizukami of Tohoku University, T. Nakano, and K. Yakushiji of AIST, K. Amemiya of KEK in Japan. 

[1] S. Nakatsuji et al., Nature 527, 212 (2015). [2] H. Tsai et al., Nature 580, 608 (2020). [3] S. Miwa et al., Small Sci. 1, 2000062 (2021). [4] S. Sakamoto et al., Phys. Rev. B 104, 134431 (2021).