Monte Carlo study of the classical Heisenberg antiferromagnet with easy-plane anisotropy on a triangular lattice

In this paper the thermodynamics of the classical Heisenberg antiferromagnet with easy-plane anisotropy on a triangular lattice is investigated by means of Monte Carlo simulations. The topological frustration and the anisotropy of the exchange interaction turn out in a rich phase diagram showing the signatures of two distinct phase transitions, i.e., a Berezinkii-Kosterlitz-Thouless transition, also present in the unfrustrated counterparts of the model and associated with the vortex-antivortex unbinding, and an Ising-like one with a discrete order parameter, the chirality. These effects of the frustration, already observed in the XY model (or planar rotator), were not yet known in the model we studied, which is, being the spins three dimensional vectors, a more realistic description of a spin system. Data are reported in a broad range of temperatures for four values of the easy-plane anisotropy and for lattice sizes ranging from 24x24 to 120x120. (C) 1999 American Institute of Physics. [S0021-8979(99)76008-1].