Multicritical behavior of two-dimensional anisotropic antiferromagnets in a magnetic field

TL;DR

This paper investigates the phase diagram and multicritical points of two-dimensional anisotropic antiferromagnets under a magnetic field, revealing complex critical behavior and the nature of transition lines.

Contribution

It provides a theoretical analysis of the multicritical behavior and phase transitions in 2D anisotropic antiferromagnets, including the nature of the multicritical point and its finite temperature occurrence.

Findings

Presence of a first-order spin-flop line starting from T=0

Multicritical point is not O(3) symmetric and occurs at finite temperature

Critical temperature varies with magnetic field and anisotropy

Abstract

We study the phase diagram and multicritical behavior of anisotropic Heisenberg antiferromagnets on a square lattice in the presence of a magnetic field along the easy axis. We argue that, beside the Ising and XY critical lines, the phase diagram presents a first-order spin-flop line starting from T=0, as in the three-dimensional case. By using field theory we show that the multicritical point where these transition lines meet cannot be O(3) symmetric and occurs at finite temperature. We also predict how the critical temperature of the transition lines varies with the magnetic field and the uniaxial anisotropy in the limit of weak anisotropy.