Ultrafast spin dynamics in Magnetic Hopfions*

Topological solitons are of high interest to condensed matter physics. In contrast to two dimensional skyrmions which have been studied intensely in both static and time-resolved experiments^1,2, magnetic Hopfions are three dimensional and were only recently observed experimentally in chiral magnetic nanodisks made from Ir/Co/Pt multilayers. The Hopfion spin texture can be described as a closed toroid of twisted skyrmion string and is expected to exhibit exotic dynamics^3,4.

Here, we present results from micromagnetic simulations using mumax3 implemented at the HPC Lawrencium supercluster at Berkeley Lab. The dynamics of magnetic Hopfions were studied under sinusoidal and pulsed magnetic field excitations. The system’s GHz spin wave spectrum is simulated over a range of applied fields, as well as its gyrational and breathing modes in the 100MHz range. These results will guide future studies of magnetic Hopfions using advanced time resolved magnetic scanning transmission x-ray microscopy techniques.

1 Woo, S. et al. Nature Materials (2016).
2 Büttner, F. et al. Nature Physics (2015).
3 Wang, X. S., Qaiumzadeh, A. & Brataas,Physical Review Letters (2019).
4 Liu, Y., Hou, W., Han, X. & Zang, Physical Review Letters (2020).