Hole-mediated ferromagnetism in tetrahedrally coordinated semiconductors

A mean field model of ferromagnetism mediated by delocalized or weakly localized holes in zincblende and wurzite diluted magnetic semiconductors is presented. The model takes into account: (i) strong spin-orbit and kp couplings in the valence band; (ii) the effect of strain upon the hole density-of-states, and (iii) the influence of disorder and carrier-carrier interactions, particularly near the metal-to-insulator transition. A quantitative comparison between experimental and theoretical results for (Ga,Mn)As demonstrates that theory describes the values of the Curie temperatures observed in the studied systems as well as explain the directions of the easy axis and the magnitudes of the corresponding anisotropy fields as a function of biaxial strain. Furthermore, the model reproduces unusual sign, magnitude, and temperature dependence of magnetic circular dichroism in the spectral region of the fundamental absorption edge. Chemical trends and various suggestions concerning design of novel ferromagnetic semiconductor systems are described.