Mean-field study ofFe2+- andCo2+-doped diluted magnetic semiconductors

Abstract

Based on a modified mean-field model, we calculate the Curie temperatures of ${\mathrm{Fe}}^{2+}$- and ${\mathrm{Co}}^{2+}$-doped diluted magnetic semiconductors (DMSs) and their dependence on the hole concentration. We find that the Curie temperatures increase with an increase in hole concentration and the relationship $T_C\propto p^{1∕3}$ also approximately holds for ${\mathrm{Fe}}^{2+}$- and ${\mathrm{Co}}^{2+}$-doped systems with moderate hole concentration. For either low or high hole concentrations, however, the $p^{1∕3}$ law is violated due to the anomalous magnetization of the ${\mathrm{Fe}}^{2+}$ and ${\mathrm{Co}}^{2+}$ ions, and the nonparabolic nature of the hole bands. Further, the values of $T_C$ for ${\mathrm{Fe}}^{2+}$- and ${\mathrm{Co}}^{2+}$-doped DMSs are significantly higher than those for ${\mathrm{Mn}}^{2+}$-doped DMSs, due to the larger exchange interaction strength.