Monte Carlo study of phase transitions in bond- and site-disordered Ising ferromagnets

By Monte Carlo simulations the phase transition is investigated for bond- and site-disordered Ising ferromagnets with special emphasis to the temperature dependence of the paramagnetic susceptibility chi 0 (T) outside the real critical temperature range. For site-disordered systems a large temperature range of deviations from the Curie-Weiss law and a non-monotonic temperature dependence of the effective exponent gamma (T)=(T-T c ) chi 0 (d chi 0 -1 /dT) was found, in close analogy with the experimentally observed behaviour of amorphous Heisenberg ferromagnets. Bond disorder affects the critical temperature T c but has little influence on the temperature dependence of chi 0 (T).