Skyrmion motion in magnetic anisotropy gradients: Acceleration caused by deformation

TL;DR

This paper investigates how strong magnetic anisotropy gradients deform skyrmions, causing acceleration and curved trajectories, and discusses implications for spintronic applications and skyrmion Hall effect suppression.

Contribution

It reveals that strong anisotropy gradients deform skyrmions, leading to acceleration and curved motion, extending understanding beyond linear energy dependence.

Findings

Skyrmions accelerate in strong anisotropy gradients.

Deformation causes skyrmions to follow curved trajectories.

Straight-line motion is achievable with specific spin-orbit torques.

Abstract

Magnetic skyrmions are nano-sized topologically non-trivial spin textures that can be moved by external stimuli such as spin currents and internal stimuli such as spatial gradients of a material parameter. Since the total energy of a skyrmion depends linearly on most of these parameters, like the perpendicular magnetic anisotropy, the exchange constant, or the Dzyaloshinskii-Moriya interaction strength, a skyrmion will move uniformly in a weak parameter gradient. In this paper, we show that the linear behavior changes once the gradients are strong enough so that the magnetic profile of a skyrmion is significantly altered throughout the propagation. In that case, the skyrmion experiences acceleration and moves along a curved trajectory. Furthermore, we show that when spin-orbit torques and material parameter gradients trigger a skyrmion motion, it can move on a straight path along the current or gradient direction. We discuss the significance of suppressing the skyrmion Hall effect for spintronic and neuromorphic applications of skyrmions. Lastly, we extend our discussion and compare it to a gradient generated by the Dzyaloshinskii-Moriya interaction.