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

Abstract

By Monte Carlo simulations the phase transition is investigated for Ising and classical Heisenberg ferromagnets with site disorder (dilution with weakly magnetic atoms) or bond disorder (continuous distribution of exchange interactions). Special emphasis is given to the temperature dependence of the paramagnetic susceptibility χ O( T) outside the asymptotic critical regime. The results are compared with experimental data for amorphous ferromagnetic alloys, which exhibit both bond and site disorder, and with the predictions of the correlated molecular field theory. For the site-disordered systems strong deviations from the Curie-Weiss behavior and a non-monotonic temperature dependence of the exponent γ( T) = ( T − T c ) χ O d χ O -1/d T may be observed as for the case of amorphous ferromagnets, whereas bond disorder has only a weak influence on χ O( T). The results are discussed from the viewpoint of the reduced local dimensionality of the diluted system.