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

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 note we go beyond Gaussian order in a fully non-perturbative 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 experiment. The thermodynamic signatures of the helimagnetic transition upon cooling from the paramagnet are qualitatively consistent with experimental findings and lend further support to the Brazovskii scenario which describes a fluctuation driven first order transition due to the abundance of soft modes.