Skyrmion Glass in a Disordered Magnetic Film

TL;DR

This paper demonstrates that high concentrations of skyrmions can be stabilized in disordered magnetic films, with their size and stability analytically modeled and numerically verified, revealing field-dependent behaviors.

Contribution

It provides a combined analytical and numerical study of skyrmion behavior in disordered magnetic films, highlighting the dependence of skyrmion size and stability on magnetic field and disorder.

Findings

Skyrmion size scales as D_R/H at low fields.

Skyrmions collapse around a critical field H_c proportional to D_R^{4/3}.

Skyrmion concentration decreases exponentially with field as exp[-(H/H_c)^{3/2}].

Abstract

We show that high concentration of skyrmions can be achieved in magnetic films with quenched disorder. A 2D system of Heisenberg spins with feromagnetic exchange, $J$, and random magnetic anisotropy of strength $D_R \ll J$ has been studied. Analytical theory for the dependence of the average skyrmion size on the magnetic field $H$, and for the stability of pinned skyrmions, is complemented by numerical studies of 2D lattices containing up to 40 million spins. At low fields the average size of the skyrmion, $\lambda$, is determined by the average size of Imry-Ma domains. On increasing the field the skyrmions first shrink, with $\lambda \propto D_R/H$, and then collapse at fields distributed around $H_c \propto D_R^{4/3}$. Concentration of the skyrmions goes down with the field as $\exp[-(H/H_c)^{3/2}]$.