Liquid-solid transition of the ferromagnetic Heisenberg fluid: Simulation, density functional, and perturbation theories

Abstract

The fluid-solid equilibrium of a system of hard spheres with embedded classical Heisenberg spins is studied by means of computer simulation and various combinations of density functional theories with the spin-spin contributions treated at the level of first-order perturbation theory. The phase boundaries are determined from the simulation data using free energy calculations in the ferromagnetic and isotropic phases. Estimates of the location of the Curie line in the solid are extracted from inspection of the evolution of magnetization with temperature. The agreement between theory and simulation is relatively good for the ferromagnetic transition and merely qualitative as far as the fluid-solid transition is concerned. The theoretical approach investigated here tends to underestimate the stability of the liquid phase.