Magneto-elastic interaction in cubic helimagnets with B20 structure

TL;DR

This paper investigates how magneto-elastic interactions in cubic B20 helimagnets influence their magnetic structure, phase transitions, and lattice modulations, providing theoretical explanations aligned with experimental observations.

Contribution

It introduces a detailed analysis of magneto-elastic effects causing phase transitions and lattice modulations in cubic helimagnets, linking theory with experimental data.

Findings

Magneto-elastic interaction causes negative contribution to spin-wave gap squared.

Competition between magnon-magnon and magneto-elastic interactions explains quantum phase transitions.

Lattice modulation at twice the helix wave-vector is driven by magneto-elastic effects.

Abstract

The magneto-elastic interaction in cubic helimagnets with B20 symmetry is considered. It is shown that this interaction is responsible for negative contribution to the square of the spin-wave gap $\Delta$ which is alone has to disrupt assumed helical structure. It is suggested that competition between positive part of $\Delta^2_I$ which stems from magnon-magnon interaction and its negative magneto-elastic part leads to the quantum phase transition observed at high pressure in $Mn Si$ and $Fe Ge$. This transition has to occur when $\Delta^2=0$. For $Mn Si$ from rough estimations at ambient pressure both parts $\Delta_I$ and $|\Delta_{ME}|$ are comparable with the experimentally observed gap. The magneto-elastic interaction is responsible also for $2\m k$ modulation of the lattice where $\m k$ is the helix wave-vector and contribution to the magnetic anisotropy. Experimental observation by $x$-ray and neutron scattering the lattice modulation allows determine the strength of anisotropic part of the magneto-elastic interaction responsible for above phenomena and the lattice helicity.