Thermal fluctuations in the conical state of monoaxial helimagnets

TL;DR

This paper investigates how thermal fluctuations influence the phase transitions and magnetic properties of monoaxial helimagnets, revealing a fluctuation-induced first-order transition and temperature-dependent pitch in systems with weak Dzyaloshinskii-Moriya interactions.

Contribution

It demonstrates that thermal fluctuations can alter the order of phase transitions and induce pitch dependence on temperature and magnetic field in monoaxial helimagnets.

Findings

Thermal fluctuations change the conical to ferromagnetic transition to first order.

In purely monoaxial systems, the conical pitch remains temperature-independent.

Weak Dzyaloshinskii-Moriya interactions cause the pitch to depend on temperature and magnetic field.

Abstract

The effect of thermal fluctuations on the phase structure of monoaxial helimagnets with external magnetic field parallel to the chiral axis is analyzed by means of a saddle point expansion of the free energy. The phase transition that separates the conical and forced ferromagnetic phases is changed to first order by the thermal fluctuations. In a purely monoaxial system the pitch of the conical state remains independent of temperature and magnetic field, as in mean field theory, even when fluctuations are taken into account. However, in presence of weak Dzyaloshinskii-Moriya interactions in the plane perpendicular to the chiral axis, thermal fluctuations induce a dependence of the pitch on temperature and magnetic field. This may serve to determine the nature of magnetic interactions in such systems.