Magnus-Induced Ratchet Effects for Skyrmions Interacting with Asymmetric Substrates

TL;DR

This paper demonstrates that skyrmions can exhibit ratchet effects, including a novel transverse ratchet induced by the Magnus term, enabling new control methods for skyrmion motion in spintronics.

Contribution

The study reveals a new Magnus-induced transverse ratchet effect in skyrmions on asymmetric substrates, expanding understanding of skyrmion dynamics and control.

Findings

Magnus term is essential for the transverse ratchet effect.

Quantized net displacement occurs in ratcheting skyrmions.

Threshold ac amplitude decreases with increasing Magnus term.

Abstract

When a particle is driven with an ac force over an asymmetric potential, it can undergo a ratchet effect that produces a net dc motion of the particle. Ratchet effects have been observed in numerous systems such as superconducting vortices on asymmetric pinning substrates. Skyrmions, stable topological spin textures with particle-like properties, have many similarities to vortices but their behavior is strongly influenced by non-disspative effects arising from a Magnus term in their equation of motion. We show using numerical simulations that pronounced ratchet effects can occur for ac driven skyrmions moving over asymmetric quasi-one-dimensional substrates. We find a new type of ratchet effect called a Magnus-induced transverse ratchet that arises when the ac driving force is applied perpendicular rather than parallel to the asymmetry direction of the substrate. This transverse ratchet effect only occurs when the Magnus term is finite, and the threshold ac amplitude needed to induce it decreases as the Magnus term becomes more prominent. Ratcheting skyrmions follow ordered orbits in which the net displacement parallel to the substrate asymmetry direction is quantized. Skyrmion ratchets represent a new ac current-based method for controlling skyrmion positions and motion for spintronic applications.