Interplay of anisotropy and frustration: triple transitions in a triangular-lattice antiferromagnet

TL;DR

This paper investigates the phase transitions in a classical Heisenberg antiferromagnet on a triangular lattice with easy-axis anisotropy, revealing three Berezinskii-Kosterlitz-Thouless transitions and complex symmetry-breaking phenomena.

Contribution

It provides a theoretical phase diagram and identifies three finite-temperature BKT transitions in a frustrated magnetic system with anisotropy, including the discovery of a sliding intermediate phase.

Findings

Three BKT transitions identified via Monte Carlo simulations.

Two transitions involve breaking of ${ m Z}_6$ symmetry.

Existence of an intermediate collinear sliding phase.

Abstract

The classical Heisenberg antiferromagnet on a triangular lattice with the single-ion anisotropy of the easy-axis type is theoretically investigated. The mean-field phase diagram in an external magnetic field is constructed. Three finite-temperature Berezinskii-Kosterlitz-Thouless transitions are found by the Monte Carlo simulations in zero field. The two upper transitions are related to the breaking of the discrete ${\mathbb Z}_{6}$ symmetry group, while the lowest transition is associated with a quasi-long-range ordering of transverse components. The intermediate collinear phase between first and second transitions is the sliding phase predicted by J. V. Jos\'e {\it et al}. [Phys. Rev. B {\bf 16}, 1217 (1977)].