Boundary twists, instabilities, and creation of skyrmions and antiskyrmions

TL;DR

This paper develops boundary conditions for magnetization near interfaces, showing how boundary twists can lead to the creation of skyrmions and antiskyrmions through local instabilities, with potential applications in magnetic memory.

Contribution

It introduces a general framework for boundary conditions that induce magnetization twists, enabling controlled creation of skyrmions and antiskyrmions via material design and local instabilities.

Findings

Boundary conditions lead to Ne9el, Bloch, or intermediate twists.

Local instabilities can generate skyrmions and antiskyrmions.

Micromagnetic simulations confirm analytical predictions.

Abstract

We formulate and study the general boundary conditions dictating the magnetization profile in the vicinity of an interface between magnets with dissimilar properties. Boundary twists in the vicinity of an edge due to Dzyaloshinskii-Moriya interactions have been first discussed in [Wilson et al., Phys. Rev. B 88, 214420 (2013)] and in [Rohart and Thiaville, Phys. Rev. B 88, 184422 (2013)]. We show that in general case the boundary conditions lead to the magnetization profile corresponding to the N\'eel, Bloch, or intermediate twist. We explore how such twists can be utilized for creation of skyrmions and antiskyrmions, e.g., in a view of magnetic memory applications. To this end, we study various scenarios how skyrmions and antiskyrmions can be created from interface magnetization twists due to local instabilities. We also show that a judicious choice of Dzyaloshinskii-Moriya tensor (hence a carefully designed material) can lead to local instabilities generating certain types of skyrmions or antiskyrmions. The local instabilities are shown to appear in solutions of the Bogoliubov-de-Gennes equations describing ellipticity of magnon modes bound to interfaces. In one considered scenario, a skyrmion-antiskyrmion pair can be created due to instabilities at an interface between materials with properly engineered Dzyaloshinskii-Moriya interactions. We use micromagnetics simulations to confirm our analytical predictions.