McPhase is a Mean-field monte-Carlo simulation program for magnetic PHASE diagrams and excitations, originally developed by Martin Rotter. For the online documentation, please see the McPhase webpage.
McPhase uses the mean-field approximation to calculate magnetic structures and magnetic-field vs temperature phase diagrams from input files which specify the crystal structure of a magnetic material and the exchange interactions between the magnetic ions in this material.
McPhase can also calculate the magnetic excitations (magnons) using the random phase approximation. The mean field and random phase approximations, as applied to local moment magnets, are described in detail in Rare Earth Magnetism by Jensen and Mackintosh.