Skyrmion lattice phase in three-dimensional chiral magnets from Monte Carlo simulations

Abstract

Chiral magnets, such as MnSi, display a rich finite temperature phase diagram in an applied magnetic field. The most unusual of the phases encountered is the so-called A Phase characterized by a triangular lattice of skyrmion tubes. Its existence cannot be captured within a mean-field treatment of a Landau-Ginzburg functional, but thermal fluctuations to Gaussian order are required to stabilize it. In this paper, we go beyond Gaussian order in a fully nonperturbative study of a three-dimensional lattice spin model using classical Monte Carlo simulations. We demonstrate that the A Phase is, indeed, stabilized by thermal fluctuations, and furthermore, we reproduce the full phase diagram found in experiments. The thermodynamic signatures of the helimagnetic transition upon cooling from the paramagnet are qualitatively consistent with experimental findings and lend further support to the BrazovskiÄ scenario, which describes a fluctuation-driven first-order transition due to the abundance of soft modes. © 2013 American Physical Society.