Short period magnetization texture of B20-MnGe explained by thermally fluctuating local moments

TL;DR

This paper investigates the unique short-range magnetic textures in MnGe, revealing that isotropic exchange interactions, rather than chiral Dzyaloshinskii-Moriya interactions, primarily govern its magnetic properties, contrasting with other B20 compounds.

Contribution

It demonstrates that MnGe's magnetic behavior is driven by isotropic exchange interactions, and introduces a model showing how higher-order interactions stabilize complex magnetic states.

Findings

MnGe's magnetic properties are explained by isotropic exchange interactions.

Comparison with FeGe validates the theoretical approach.

Higher-order interactions stabilize triple-q magnetic states.

Abstract

B20-type compounds, such as MnSi and FeGe, host helimagnetic and skyrmion phases at the mesoscale, which are canonically explained by the combination of ferromagnetic isotropic interactions with weaker chiral Dzyaloshinskii-Moriya ones. Mysteriously, MnGe evades this paradigm as it displays a noncollinear magnetic state at a much shorter nanometer scale. Here we show that the length scale and volume-dependent magnetic properties of MnGe stem from purely isotropic exchange interactions, generally obtained in the paramagnetic state. Our approach is validated by comparing MnGe with the canonical B20-helimagnet FeGe. The free energy of MnGe is calculated, from which we show how triple-q magnetic states can stabilize by adding higher-order interactions.