Unified Theory of Magnetoelastic Effects in B20 chiral magnets

TL;DR

This paper develops a comprehensive thermodynamic model for B20 chiral magnets, explaining magnetoelastic effects and skyrmion behavior under stress, with results matching experimental data and enabling future research.

Contribution

It introduces a unified theoretical framework incorporating higher order interactions to describe magnetoelastic phenomena in B20 helimagnets.

Findings

Phase diagram of MnSi under stress matches experiments

Elastic constants vary with magnetic field as predicted

Skyrmion stability is sensitive to mechanical loads

Abstract

A magnetic skyrmion is a spin whirl with topological protection and high mobility to electric current. Intrinsic magnetoelastic coupling in chiral magnets permits manipulation of magnetic skyrmions and their lattice using mechanical loads, which is essential for developing future spintronics devices. It is found in experiments that the stability and deformation of skyrmions are sensitive to stresses, while the appearance of magnetic skyrmions in turn has a significant effect on the mechanical properties of the underlying material. However, a theory which explains these related phenomena within a unified framework is not seen. Here we construct a thermodynamic model for B20 helimagnets incorporating a magnetoelastic functional with necessary higher order interactions derived by group theory. Within the model, we establish the methodology to calculate the phase diagram and equilibrium properties of helimagnets under coupled temperature-magneto-elastic field. Applying the model to bulk MnSi, we calculate the temperature-magnetic field phase diagram under stress-free condition and its variation when uniaxial compression is applied. We also calculate the variation of all the elastic constants with magnetic field. The results obtained agree quantitatively with corresponding experiments. Our model provides a reliable basis for further theoretical studies concerning any magnetoelastic related phenomena in chiral magnets.