Phase diagram of Heisenberg fluids: Computer simulation and density functional theory

We have investigated equilibrium phases of a class of ferromagnetic Heisenberg fluids using computer simulations and a modified mean-field approximation. In the latter, configurations in the average of the perturbative part of the energy are weighted by the zero-density approximation of the pair distribution function. Although the theoretical results suggest a phase diagram with a tricritical point, the simulations provide some evidence for a magnetic critical point. Owing to finite size effects, however, the existence of a tricritical point cannot be ruled out.