Ordered Phases of Itinerant Dzyaloshinsky-Moriya Magnets and Their Electronic Properties

TL;DR

This paper develops a mean-field field theory for Dzyaloshinsky-Moriya magnets like MnSi and FeGe, analyzing their phase diagram, magnetic phases, Goldstone modes, and electronic properties, including transport and thermodynamics.

Contribution

It introduces a comprehensive mean-field framework for understanding the phase diagram and electronic properties of itinerant Dzyaloshinsky-Moriya magnets.

Findings

Identification of phase transitions in helical and conical phases

Derivation of Goldstone modes and their effects on electronic properties

Analysis of transport differences between helimagnets and ferromagnets

Abstract

A field theory appropriate for magnets that display helical order due to the Dzyaloshinsky-Moriya mechanism, a class that includes MnSi and FeGe, is used to derive the phase diagram in a mean-field approximation. The helical phase, the conical phase in an external magnetic field, and recent proposals for the structure of the A-phase and the non-Fermi-liquid region in the paramagnetic phase are discussed. It is shown that the orientation of the helical pitch vector along an external magnetic field within the conical phase occurs via two distinct phase transitions. The Goldstone modes that result from the long-range order in the various phases are determined, and their consequences for electronic properties, in particular the specific heat, the single-particle relaxation time, and the electrical and thermal conductivities, are derived. Various aspects of the ferromagnetic limit, and qualitative differences between the transport properties of helimagnets and ferromagnets, are also discussed.