  We consider a mean-field approach to the hole-mediated ferromagnetism in
III-V Mn-based semiconductor compounds to discuss the dependence of the hole
density on that of Mn sites in Ga_{1-x}Mn_xAs. The hole concentration, p, as a
function of the fraction of Mn sites, x, is parametrized in terms of the
product m*J_{pd}^2 (where m* is the hole effective mass and J_{pd} is the
Kondo-like hole/local-moment coupling), and the critical temperature Tc. By
using experimental data for these quantities, we have established the
dependence of the hole concentration with x, which can be associated with the
occurrence of a reentrant metal-insulator transition taking place in the hole
gas. We also calculate the dependence of the Mn magnetization with x, for
different temperatures (T), and found that as T increases, the width of the
composition-dependent magnetization decreases drammatically, and that the
magnetization maxima also decreases, indicating the need for quality-control of
Mn-doping composition in diluted magnetic semiconductor devices.
