First-Principles Evaluation of the Dzyaloshinskii--Moriya Interaction

TL;DR

This paper reviews three first-principles methods for calculating the Dzyaloshinskii--Moriya interaction, illustrating their application to chiral ferromagnets and clarifying their theoretical foundations.

Contribution

It compares and discusses three different first-principles approaches to evaluate the DM interaction, providing insights into their practical application to real materials.

Findings

All three methods successfully calculate the DM interaction in chiral magnets.

The spin gauge field approach links DM to equilibrium spin currents.

Perturbation expansion extends RKKY interaction to noncentrosymmetric systems.

Abstract

We review recent developments of formulations to calculate the Dzyaloshinskii--Moriya (DM) interaction from first principles. In particular, we focus on three approaches. The first one evaluates the energy change due to the spin twisting by directly calculating the helical spin structure. The second one employs the spin gauge field technique to perform the derivative expansion with respect to the magnetic moment. This gives a clear picture that the DM interaction can be represented as the spin current in the equilibrium within the first order of the spin-orbit couplings. The third one is the perturbation expansion with respect to the exchange couplings and can be understood as the extension of the Ruderman--Kittel--Kasuya--Yosida (RKKY) interaction to the noncentrosymmetric spin-orbit systems. By calculating the DM interaction for the typical chiral ferromagnets Mn$_{1-x}$Fe$_x$Ge and Fe$_{1-x}$Co$_x$Ge, we discuss how these approaches work in actual systems.