Mean-field approach to ferromagnetism in (III,Mn)V diluted magnetic semiconductors at low carrier densities

We present a detailed study, within the mean-field approximation, of an impurity band model for III-V diluted magnetic semiconductors. Such a model should be relevant at low carrier densities, below and near the metal-insulator transition. Positional disorder of the magnetic impurities inside the host semiconductor is shown to have observable consequences for the shape of the magnetization curve. Below the critical temperature the magnetization is spatially inhomogeneous, leading to very unusual temperature and magnetic field dependence of the average magnetization as well as specific heat. A metal-insulator transition is also observed, with a mobility edge inside the impurity band, in agreement with experimental measurements.