Disorder and ferromagnetism in diluted magnetic semiconductors

We have investigated the interplay between disorder and ferromagnetism in III_1-xMn_x V semiconductors. Our study is based on a model in which S = 5/2 Mn local moments are exchange coupled to valence-band holes that interact via Coulomb interactions with each other, with ionized Mn acceptors, and with the antisite defects present in these materials. We find quasiparticle participation ratios consistent with a metal-insulator transition that occurs in the ferromagnetic state near x∼0.01. By evaluating the distribution of exchange mean fields at Mn moment sites, we provide evidence in favor of the applicability of impurity-band magnetic-polaron and hole-fluid models on insulating and metallic sides of the phase transition, respectively.