Phase Diagram of a Classical, Anisotropic Heisenberg Antiferromagnet in a Field

We study a classical, anisotropic Heisenberg antiferromagnet in a field by Monte Carlo methods. We calculate the transverse and longitudinal antiferromagnetic order parameters as function of temperature and axial magnetic field in order to obtain the phase diagram in the field-temperature plane consisting of antiferromagnetic-, spin-flop-, and saturated paramagnetic phase. For zero temperature the critical fields can be calculated analytically. Crossing the spin flop phase by varying the temperature, the magnetic specific heat shows two peaks.