Phase-transitions induced by easy-plane anisotropy in the classical Heisenberg antiferromagnet on a triangular lattice: a Monte Carlo simulation

TL;DR

This study uses Monte Carlo simulations to analyze phase transitions in a frustrated classical Heisenberg antiferromagnet with easy-plane anisotropy on a triangular lattice, revealing Berezinskii-Kosterlitz-Thouless and Ising-like transitions.

Contribution

It provides detailed simulation data on how easy-plane anisotropy influences phase transitions and critical temperatures in a frustrated triangular lattice antiferromagnet.

Findings

Identification of Berezinskii-Kosterlitz-Thouless transition signatures.

Detection of Ising-like transition associated with chirality.

Transition temperatures decrease as anisotropy weakens.

Abstract

We present the results of Monte Carlo simulations for the antiferromagnetic classical XXZ model with easy-plane exchange anisotropy on the triangular lattice, which causes frustration of the spin alignment. The behaviour of this system is similar to that of the antiferromagnetic XY model on the same lattice, showing the signature of a Berezinskii-Kosterlitz-Thouless transition, associated to vortex-antivortex unbinding, and of an Ising-like one due to the chirality, the latter occurring at a slightly higher temperature. Data for internal energy, specific heat, magnetic susceptibility, correlation length, and some properties associated with the chirality are reported in a broad temperature range, for lattice sizes ranging from 24x24 to 120x120; four values of the easy-plane anisotropy are considered. Moving from the strongest towards the weakest anisotropy (1%) the thermodynamic quantities tend to the isotropic model behaviour, and the two transition temperatures decrease by about 25% and 22%, respectively.