Inertia, diffusion and dynamics of a driven skyrmion

TL;DR

This study investigates the dynamic behavior of skyrmions in chiral magnets, revealing negligible inertia and frequency-dependent responses, which support their potential for stable, fast information storage applications.

Contribution

The paper combines numerical simulations and analytical analysis to show that skyrmion inertia is negligible and their response to dynamic forces is governed by an effective mass and damping, advancing understanding of their dynamics.

Findings

Inertial effects are almost absent in driven skyrmion dynamics.

Skyrmion response depends on frequency, with an effective mass and damping.

Thermal diffusion is suppressed by cyclotron motion and proportional to damping.

Abstract

Skyrmions recently discovered in chiral magnets are a promising candidate for magnetic storage devices because of their topological stability, small size ($\sim 3-100$nm), and ultra-low threshold current density ($\sim 10^{6}$A/m$^2$) to drive their motion. However, the time-dependent dynamics has hitherto been largely unexplored. Here we show, by combining the numerical solution of the Landau-Lifshitz-Gilbert equation and the analysis of a generalized Thiele's equation, that inertial effects are almost completely absent in skyrmion dynamics driven by a time-dependent current. In contrast, the response to time-dependent magnetic forces and thermal fluctuations depends strongly on frequency and is described by a large effective mass and a (anti-) damping depending on the acceleration of the skyrmion. Thermal diffusion is strongly suppressed by the cyclotron motion and is proportional to the Gilbert damping coefficient $\alpha$. This indicates that the skyrmion position is stable, and its motion responds to the time-dependent current without delay or retardation even if it is fast. These findings demonstrate the advantages of skyrmions as information carriers.