Edge instabilities and skyrmion creation in magnetic layers

TL;DR

This paper investigates edge instabilities in two-dimensional ferromagnets with Dzyaloshinskii-Moriya interactions, revealing how edge-bound magnons lead to helical phases and skyrmion creation near the edges.

Contribution

It provides an analytical and numerical analysis of edge instabilities and demonstrates controlled skyrmion creation in magnetic layers with DM interactions.

Findings

Edge-bound magnon states exist in the field-polarized phase.

Lowering magnetic field causes edge magnons to condense and induce local instability.

Edge instability leads to formation of helical phases and skyrmions near the boundary.

Abstract

We study both analytically and numerically the edge of two-dimensional ferromagnets with Dzyaloshinskii-Moriya (DM) interactions, considering both chiral magnets and magnets with interface-induced DM interactions. We show that in the field-polarized ferromagnetic phase magnon states exist which are bound to the edge, and we calculate their spectra within a continuum field theory. Upon lowering an external magnetic field, these bound magnons condense at a finite momentum and the edge becomes locally unstable. Micromagnetic simulations demonstrate that this edge instability triggers the creation of a helical phase which penetrates the field-polarized state within the bulk. A subsequent increase of the magnetic field allows to create skyrmions close to the edge in a controlled manner.