Cubic magnets with Dzyaloshinskii-Moriya interaction at low T

TL;DR

This paper theoretically analyzes the ground state and spin-wave spectrum of cubic Dzyaloshinskii-Moriya magnets like MnSi and FeGe, revealing strong anisotropy, instability under certain fields, and the effects of anisotropy and interactions.

Contribution

It develops a linear spin-wave theory for cubic DMI magnets, accounting for anisotropy and interactions, and discusses experimental implications.

Findings

Spin-wave spectrum depends strongly on magnetic field and anisotropy.

Spectrum is unstable at infinitesimal perpendicular field without a gap.

Introducing a gap stabilizes the spectrum, influenced by cubic anisotropy and interactions.

Abstract

Ground state and spin-wave spectrum of cubic magnets with the Dzyaloshinskii-Moriya interaction (DMI) such as MnSi and FeGe are studied theoretically. The linear spin-wave theory is developed. The spin-wave spectrum depends strongly on the magnetic field and strongly anisotropic. It is a result of incommensurate magnetic structure when the DMI breaks the total spin conservation law. The spin-wave spectrum is unstable at infinitesimal perpendicular field. If the gap $\Delta$ is introduced the spectrum becomes stable. The gap appears due to cubic anisotropy and the spin-wave interaction considered in the Hartree-Fock approximation. Peculiar properties of the ESR and neutron scattering in the helical magnets are considered and possibilities of corresponding experimental studies are discussed.