MONTE-CARLO STUDY OF THE 2-DIMENSIONAL QUADRATIC ISING FERROMAGNET WITH SPINS S = 1 2 AND S = 1 AND WITH CRYSTAL-FIELD INTERACTIONS/

The single-spin-flip Metropolis Monte Carlo algorithm is applied to an Ising ferromagnet with mixed spins of S = 1/2 and S = 1 and a crystal -field interaction. The critical temperatures and exponents both in th e absence and presence of the crystal-field interaction are investigat ed with finite-size scaling theory. The critical temperature that we o btained in zero crystal field is very close to the high-temperature se ries-expansion result. The finite-size scaling results for the critica l exponents yield the two-dimensional Ising-model values, which are in good agreement with those suggested by the universality hypothesis. T he phase diagram of this model is obtained and comparisons are made wi th other approximate methods when available.