Rotating skyrmion lattices by spin torques and field or temperature gradients

TL;DR

This paper develops a theoretical framework explaining how small electric currents and gradients can induce rotation of skyrmion lattices in chiral magnets, supported by neutron scattering experiments.

Contribution

It introduces a model combining Landau-Lifshitz-Gilbert equations with damping and pinning effects to explain skyrmion lattice rotation under external stimuli.

Findings

Finite-angle rotation up to 15 degrees observed

Continuous rotation with angular velocity occurs at larger gradients

Experimental data confirms easy rotation with small currents and temperature gradients

Abstract

Chiral magnets like MnSi form lattices of skyrmions, i.e. magnetic whirls, which react sensitively to small electric currents j above a critical current density jc. The interplay of these currents with tiny gradients of either the magnetic field or the temperature can induce a rotation of the magnetic pattern for j>jc. Either a rotation by a finite angle of up to 15 degree or -- for larger gradients -- a continuous rotation with a finite angular velocity is induced. We use Landau-Lifshitz-Gilbert equations extended by extra damping terms in combination with a phenomenological treatment of pinning forces to develop a theory of the relevant rotational torques. Experimental neutron scattering data on the angular distribution of skyrmion lattices suggests that continuously rotating domains are easy to obtain in the presence of remarkably small currents and temperature gradients.