Uniaxially anisotropic antiferromagnets in a field on a square lattice

TL;DR

This paper investigates the phase behavior of uniaxially anisotropic antiferromagnets on a square lattice using ground state analysis and Monte Carlo simulations, revealing effects of anisotropy and fluctuations on phase stability.

Contribution

It provides new insights into how single-ion anisotropy influences non-collinear structures and the nature of phase transitions in anisotropic antiferromagnets.

Findings

Single-ion anisotropy affects biconical phase stability.

Degenerate bidirectional fluctuations dominate the XY model transition region.

Phase diagram resembles that of the XXZ model without single-ion anisotropy.

Abstract

Classical uniaxially anisotropic Heisenberg and XY antiferromagnets in a field along the easy axis on a square lattice are analysed, applying ground state considerations and Monte Carlo techniques. The models are known to display antiferromagnetic and spin-flop phases. In the Heisenberg case, a single-ion anisotropy is added to the XXZ antiferromagnet, enhancing or competing with the uniaxial exchange anisotropy. Its effect on the stability of non-collinear structures of biconical type is studied. In the case of the anisotropic XY antiferromagnet, the transition region between the antiferromagnetic and spin-flop phases is found to be dominated by degenerate bidirectional fluctuations. The phase diagram is observed to resemble closely that of the XXZ antiferromagnet without single-ion anisotropy.