Interplay between carrier localization and magnetism in diluted magnetic and ferromagnetic semiconductors

The presence of localized spins exerts a strong influence on quantum localization in doped semiconductors. At the same time carrier-mediated interactions between the localized spins are modified or even halted by carriers' localization. The interplay of these effects is discussed for II-VI and III-V diluted magnetic semiconductors. This insight is exploited to interpret the complex dependence of resistance on temperature, magnetic field, and concentration of valence-band holes in (Ga,Mn)As. In particular, high field negative magnetoresistance results from the orbital weak localization effect. The resistance maximum and the associated negative magnetoresistance near the Curie temperature are assigned to the destructive influence of preformed ferromagnetic bubbles on the "antilocalization" effect driven by disorder-modified carrier-carrier interactions. These interactions account also for the low-temperature increase of resistance. Furthermore, the sensitivity of conductance to spin splitting and to scattering by spin disorder may explain resistance anomalies at coercive fields, where relative directions of external and molecular fields change.