Hopfion Dynamics in Chiral Magnets

Resonant spin dynamics of topological spin textures are hugely correlated with their topological nature and can be employed to understand nature, which attracts interest in condensed matter physics and memory and storage technology [1]. Among topological spin textures, skyrmions and vortices have been heavily studied, but hopfions have been paid little attention thus far. In this study, we present a numerical resonant study of spin dynamics of a three-dimensional topological spin texture hopfion in a B20 chiral magnet. Recent studies proposed to use interfaces with strong perpendicular magnetic anisotropy adjacent to a B20 FeGe nanodisk to stabilize hopfions [2]. In our study, using micromagnetic simulations, we first identified the ground state spin configurations of a hopfion, effects of anisotropies, geometric confinements and demagnetizing fields. Then, we calculated the resonance frequencies and spin-wave modes of spin precession dynamics. Our work helps to guide experimental studies to identify 3-dimensional topological spin texture of hopfions in chiral magnets in a functioning device, where imaging is not possible.

[1] N. Nagaosa and Y. Tokura, Nat. Nanotechnol. 8, 899 (2013).
[2] J.-S.B. Tai, P.J. Ackerman, and I.I. Smalyukh, Proc. Natl. Acad. Sci. 115, 921 (2018).