Chiral skyrmion auto-oscillations in a ferromagnet under spin transfer torque

TL;DR

This paper demonstrates that a skyrmion in a ferromagnetic nanodisc can be driven into steady rotational auto-oscillations by uniform spin transfer torque, enabled by chiral symmetry breaking from Dzyaloshinskii-Moriya interaction.

Contribution

It provides a theoretical and numerical analysis of chiral skyrmion auto-oscillations induced by spin torque, highlighting the role of chiral symmetry breaking.

Findings

Skyrmions exhibit steady rotational motion under uniform spin torque.

Auto-oscillations arise from coupling between rotation and breathing modes.

Chiral DM interaction enables the system to function as a spin-torque oscillator.

Abstract

A skyrmion can be stabilized in a nanodisc geometry in a ferromagnetic material with Dzyaloshinskii-Moriya (DM) interaction. We apply spin torque uniform in space and time and observe numerically that the skyrmion is set in steady rotational motion around a point off the nanodisc center. We give a theoretical description of the emerging auto-oscillation dynamics based on the coupling of the rotational motion to the breathing mode of the skyrmion and to the associated oscillations of the in-plane magnetization. The analysis shows that the achievement of auto-oscillations in this simple set-up is due to the chiral symmetry breaking. Thus, we argue that the system is turned into a spin-torque oscillator due to the chiral DM interaction.