Study of the phase diagram and the critical behaviour of the 2D Heisenberg antiferromagnet with small uniaxial anisotropy

Abstract

We determined a discontinuous character of the field-induced phase transition between the Ising-like and the XY-like phase of the classical two-dimensional Heisenberg antiferromagnet with a small uniaxial anisotropy (UHAF) by Monte Carlo simulations. Additional neutron scattering experiments on Rb 2MnCl 4 yield a description of the critical behaviour of the 2D model system and show a quite good accordance between an experimentally determined 2D phase diagram and a theoretical description of the phase boundaries used so far only for the 3D model system.