Optically excited spin dynamics of thermally metastable skyrmions in Fe$_{0.75}$Co$_{0.25}$Si

TL;DR

This study explores the microwave spin excitations of skyrmion states in Fe$_{0.75}$Co$_{0.25}$Si, revealing that metastable skyrmions exhibit dynamic properties similar to equilibrium states, with implications for applications and fundamental research.

Contribution

It demonstrates that metastable skyrmion states can be dynamically similar to equilibrium states, expanding understanding of skyrmion behavior far from thermal equilibrium.

Findings

Precessional and exponential dynamic responses observed in both equilibrium and metastable skyrmion states.

Precession frequencies in metastable and equilibrium states are in excellent agreement when scaled with temperature.

Metastable skyrmions show potential for flexible microwave applications and fundamental studies.

Abstract

We investigate the microwave spin excitations of the cubic chiral magnet Fe$_{0.75}$Co$_{0.25}$Si as driven by the thermal modulation of magnetic interactions via laser heating and probed by time-resolved measurements of the magneto-optical Kerr effect. Focusing on the topologically nontrivial skyrmion lattice state, the dynamic properties in thermodynamic equilibrium are compared with those of a metastable state prepared by means of rapid field cooling. In both cases, we find precessional and exponential contributions to the dynamic response, characteristic of a breathing mode and energy dissipation, respectively. When taking into account the universal scaling as a function of temperature, the precession frequencies in the equilibrium and metastable skyrmion state are in excellent quantitative agreement. This finding highlights that skyrmion states far from thermal equilibrium promise great flexibility, for instance with respect to temperature and field scales, both for possible microwave applications and the study of fundamental properties.