In this study, the electronic and magnetic properties of dilute magnetic semiconductors (DMS) have been investigated by ab initio calculations and statistical methods.
Based on the Korringa-Kohn-Rostoker coherent potential approximation (KKR-CPA) method and using the magnetic force theorem, we have calculated the electronic structures and exchange coupling constants in Cr doped II-VI type DMSs. The calculated exchange coupling constants indicate that the magnetic interaction is rather short ranged due to the fact that the Cr doped II-VI type DMSs are stabilized by the ferromagnetic double exchange interaction. Curie temperatures of II-VI type DMSs have been estimated by using the several statistical methods. It is known that Monte Carlo simulation which can take the magnetic percolation effect into consideration provides the accurate estimation of Curie temperature. Actually, the Curie temperatures of (Zn,Cr)Te calculated by the Monte Carlo simulation are in good agreement with experimental values.
Furthermore, the effects of inhomogeneous distribution of magnetic impurities originated from spinodal decomposition on magnetism in the DMS have been discussed, and the methods for describing the spinodal decomposition in the DMS have been developed. In order to simulate the spinodal decomposition in the DMS by the Monte Carlo method, the effective pair interactions between magnetic impurities have been calculated by the generalized perturbation method in the KKR-CPA. The calculated effective pair interactions of (Ga,Mn)As, (Zn,Cr)Te, and Co(Ti,Mn)Sb show that attractive interactions work between magnetic impurities. It has turned out from the simulation results that the magnetic impurities in the DMS form quasi-one-dimensional nanomagnets with large shape anisotropy and high blocking temperature under the layer-by-layer crystal growth condition even if impurity concentration is low. Finally, a new fabrication process has been designed for realizing the Tera-bit-density nanomagnets in the DMS by controlling the self-organized two-dimensional spinodal decomposition.