PHASE-DIAGRAM OF HEISENBERG FLUIDS - COMPUTER-SIMULATION AND DENSITY-FUNCTIONAL THEORY

We have investigated equilibrium phases of a class of ferromagnetic He isenberg fluids using computer simulations and a modified mean-held ap proximation. In the latter, configurations in the average of the pertu rbative part of the energy are weighted by the zero-density approximat ion of the pair distribution function. Although the theoretical result s suggest a phase diagram with a tricritical point, the simulations pr ovide some evidence for a magnetic critical point. Owing to finite siz e effects, however, the existence of a tricritical point cannot be rul ed out.