Topological Transitions, Pinning and Ratchets for Driven Magnetic Hopfions in Nanostructures

TL;DR

This paper investigates the dynamics of magnetic hopfions in nanostructures, revealing topological transitions, pinning effects, and ratchet behavior under various defect configurations and external currents through atomistic simulations.

Contribution

It introduces a detailed simulation study of hopfion interactions with defects, uncovering new topological states and controlled motion mechanisms in magnetic nanostructures.

Findings

Identification of pinned, sliding, and transformed toron phases.

Demonstration of a ratchet effect with net dc motion under ac driving.

Observation of hopfions moving without a Hall angle, while torons do with a Hall angle.

Abstract

Using atomistic simulations, we examine the dynamics of three-dimensional magnetic hopfions interacting with an array of line defects or posts as a function of defect spacing, defect strength, and current. We find a pinned phase, a sliding phase where a hopfion can move through the posts or hurdles by distorting, and a regime where the hopfion becomes compressed and transforms into a toron that is half the size of the hopfion and moves at a lower velocity. The toron states occur when the defects are strong; however, in the toron regime, it is possible to stabilize sliding hopfions by increasing the applied current. Hopfions move without a Hall angle, while the toron moves with a finite Hall angle. We also show that when a hopfion interacts with an asymmetric array of planar defects, a ratchet effect consisting of a net dc motion can be realized under purely ac driving.