Monte Carlo study of the critical behavior of pure and site-diluted Ising ferro- and ferrimagnets

Monte Carlo simulations are performed for pure and site-diluted Ising ferro- and ferrimagnets on a simple cubic lattice with up to 40/sup 3/ sites and with impurity concentration x. For the diluted ferromagnet (x = 0.2) the exponent ..beta.. = 0.392 +- 0.03 is definitely larger than the pure model value of ..beta.. = 0.304 +- 0.03. In the contrast, for ferrimagnetic systems (x = 0, 0.1, 0.2) the ..beta.. values appear to be independent of x and within the error limits consistent with the value for the pure ferromagnet, possibly because the width of the asymptotic random critical regime (or of the crossover regime) is even smaller than in the case of ferromagnets.