Phase diagrams of a classical two-dimensional Heisenberg antiferromagnet with single-ion anisotropy

TL;DR

This paper analyzes a classical 2D anisotropic Heisenberg antiferromagnet model using Monte Carlo simulations, revealing detailed phase diagrams, defect behaviors, and the effects of external magnetic fields, aligning with neutron scattering experimental data.

Contribution

It provides the first comprehensive phase diagrams of the classical 2D anisotropic Heisenberg model with external fields, including defect dynamics and phase transitions, matching experimental observations.

Findings

Identification of antiferromagnetic and spin-flop phases.

Observation of stripe formation and breakup of holes.

External fields induce spin-flop transitions.

Abstract

A classical variant of the two-dimensional anisotropic Heisenberg model reproducing inelastic neutron scattering experiments on La_5 Ca_9 Cu_24 O_41 [M. Matsuda et al., Phys.Rev. B 68, 060406(R) (2003)] is analysed using mostly Monte Carlo techniques. Phase diagrams with external fields parallel and perpendicular to the easy axis of the anisotropic interactions are determined, including antiferromagnetic and spin-flop phases. Mobile spinless defects, or holes, are found to form stripes which bunch, debunch and break up at a phase transition. A parallel field can lead to a spin-flop phase.