Controlling skyrmion helicity via engineered Dzyaloshinskii-Moriya interactions

TL;DR

This paper develops a theoretical framework to control and understand skyrmion helicity dynamics in chiral magnets with engineered inhomogeneous Dzyaloshinskii-Moriya interactions, highlighting potential applications in magnetic storage.

Contribution

It introduces a generalized Thiele's equation incorporating helicity as a dynamic variable for skyrmions with spatially varying DMI, advancing the modeling of skyrmion behavior.

Findings

Helicity influences skyrmion Hall angle.

Position and helicity dynamics depend on DMI inhomogeneity.

Model applied to specific engineered DMI profiles.

Abstract

Single magnetic skyrmion dynamics in chiral magnets with a spatially inhomogeneous Dzyaloshinskii-Moriya interaction (DMI) is considered. Based on the relation between DMI coupling and skyrmion helicity, it is argued that the latter must be included as an extra degree of freedom in the dynamics of skyrmions. An effective description of the skyrmion dynamics for an arbitrary inhomogeneous DMI coupling is obtained through the collective coordinates method. The resulting generalized Thiele's equation is a dynamical system for the center of mass position and helicity of the skyrmion. It is found that the dissipative tensor and hence the Hall angle become helicity dependent. The skyrmion position and helicity dynamics are fully characterized by our model in two particular examples of engineered DMI coupling: half-planes with opposite-sign DMI and linearly varying DMI. In light of the experiment of Shibata {\it et al}. [Nature Nanotech. {\bf 8}, 723 (2013)] on the magnitude and sign of the DMI, our results constitute the first step toward a more complete understanding of the skyrmion helicity as a new degree of freedom that could be harnessed in future high-density magnetic storage and logic devices.