Two-dimensional anisotropic Heisenberg antiferromagnet in a field

TL;DR

This paper investigates the phase transitions of a classical two-dimensional anisotropic Heisenberg antiferromagnet in a magnetic field using Monte Carlo simulations, revealing complex phase behavior including ordered, spin-flop, and disordered phases.

Contribution

It provides detailed Monte Carlo analysis of phase transitions in a classical 2D anisotropic Heisenberg antiferromagnet, clarifying the phase diagram and comparing with quantum models.

Findings

Identification of long-range ordered antiferromagnetic phase

Discovery of an algebraically ordered spin-flop phase

Existence of a narrow disordered phase between ordered phases

Abstract

The classical, square lattice, uniaxially anisotropic Heisenberg antiferromagnet in a magnetic field parallel to the easy axis is studied using Monte Carlo techniques. The model displays a long-range ordered antiferromagnetic, an algebraically ordered spin-flop, and a paramagnetic phase. The simulations indicate that a narrow disordered phase intervenes between the ordered phases down to quite low temperatures. Results are compared to previous, partially conflicting findings on related classical models as well as the quantum variant with spin S=1/2.