  We have investigated the interplay between the metal-insulator transition and
ferromagnetism in $({\rm III}_{1-x},{\rm Mn}_x){\rm V}$ ferromagnetic
semiconductors. Our study is based on a model in which $S=5/2$ Mn local moments
are exchange-coupled to band electrons that interact via Coulomb interactions
which each other, with ionized Mn acceptors, and with the antisite defects
present in these materials. We find quasiparticle participation ratios that are
consistent with a metal-insulator transition that occurs in the ferromagnetic
state near $x \sim 0.01$. By evaluating the distribution of mean-field exchange
coupling strengths at Mn moment sites, we provide evidence in favor of the
applicability of small polaron and hole gas models on insulating and metallic
sides of the phase transition respectively.

Condensed Matter