The Monte-Carlo algorithm is an effective method to study the Curie
temperature of a ferromagnetic system related to its exchange constant,
magnetic moment, and co-ordination number. Curie temperatures of the three
types of ferromagnetic systems are calculated, e.g., the hexagonal crystal
system, the tetragonal sys-tem, and the orthorhombic system. In order to
make the calculated magnetic moment-temperature curve fit a steep slope,
the size of the supercell of the ferro-magnetic system is selected as small
as possible, and Monte-Carlo steps are per-formed 5000000 times at each
temperature. The calculation reveals a significant result: the Curie
temperature scales with the exchange constant and the square of the magnetic
moment.