Fluctuations and Pinning for Individually Manipulated Skyrmions

TL;DR

This study numerically investigates skyrmion dynamics under various conditions, revealing noise characteristics, pinning effects, and complex depinning behaviors influenced by skyrmion interactions and quenched disorder.

Contribution

It provides new insights into skyrmion depinning thresholds, noise signatures, and the interplay between disorder and elastic interactions in skyrmion lattices.

Findings

Broad band noise with 1/f characteristic near depinning

Pinning sites cause skyrmion motion to be faster than in disorder-free systems

Reentrant pinned phases emerge due to competing pinning mechanisms

Abstract

We numerically examine the dynamics of individually dragged skyrmions interacting simultaneously with an array of other skyrmions and quenched disorder. For drives just above depinning, we observe a broad band noise signal with a $1/f$ characteristic, while at higher drives, narrow band or white noise appears. Even in the absence of quenched disorder, the threshold force that must be applied to translate the driven skyrmion is finite due to elastic interactions with other skyrmions. The depinning threshold increases as the strength of the quenched disorder is raised. Above the depinning force, the skyrmion moves faster in the presence of quenched disorder than in a disorder-free system since the pinning sites prevent other skyrmions from being dragged along with the driven skyrmion. For strong pinning, we find a stick-slip motion of the driven skyrmion which produces a telegraph noise signature. The depinning threshold increases monotonically with skyrmion density in the absence of quenched disorder, but when pinning is present, the depinning threshold changes nonmonotonically with skyrmion density and there are reentrant pinned phases due to a competition between pinning induced by the quenched disorder and that produced by the elastic interactions of the skyrmion lattice.