Electronic structure, exchange interactions and Curie temperature in diluted III-V magnetic semiconductors: (GaCr)As, (GaMn)As, (GaFe)As

摘要

We complete our earlier (Phys. Rev. B, {\bf 66}, 134435 (2002)) study of theelectronic structure, exchange interactions and Curie temperature in (GaMn)Asand extend the study to two other diluted magnetic semiconductors (GaCr)As and(GaFe)As. Four concentrations of the 3d impurities are studied: 25%, 12.5%,6.25%, 3.125%. (GaCr)As and (GaMn)As are found to possess a number of similarfeatures. Both are semi-metallic and ferromagnetic, with similar properties ofthe interatomic exchange interactions and the same scale of the Curietemperature. In both systems the presence of the charge carriers is crucial forestablishing the ferromagnetic order. An important difference between twosystems is in the character of the dependence on the variation of the number ofcarriers. The ferromagnetism in (GaMn)As is found to be very sensitive to thepresence of the donor defects, like As$_{\rm Ga}$ antisites. On the other hand,the Curie temperature of (GaCr)As depends rather weakly on the presence of thistype of defects but decreases strongly with decreasing number of electrons. Wefind the exchange interactions between 3d atoms that make a major contributioninto the ferromagnetism of (GaCr)As and (GaMn)As and propose an exchange pathresponsible for these interactions. The properties of (GaFe)As are found todiffer crucially from the properties of (GaCr)As and (GaMn)As. (GaFe)As doesnot show a trend to ferromagnetism and is not half-metallic that makes thissystem unsuitable for the use in spintronic semiconductor devices.