| As a good candidate for spintronic applications, diluted magnetic semiconductors (DMS) have been widely investigated in the past several years.;The effect of disorder inherent in the DMS system on the ferromagnetism in these materials is studied. Large dispersion in the pairwise exchange interactions is shown. The dispersion strongly reduces Curie temperature of these materials. Clustering due to the annealing process further decreases Tc. With all the factors taken into account, Tc is reasonably predicted by the local spin-density approximation in manganese(Mn) doped gallium arsenide (GaAs) ((GaMn)As).;Based on the result of (GaMn)As, two kinds of ternary alloy systems, manganese and chromium (Cr) co-doped GaAs ((Ga,Mn,Cr)As) and Mn and phosphorus (P) co-doped GaAs ((GaMn)(AsP)) are predicted to have higher Tc by double-exchange and Ruderman Kittel-Kasuya-Yosida (RKKY) models. LSDA calculations are used to test the prediction. The results show that neither co-doping Mn with Cr, nor alloying As with P improves Tc.;Another approach to increase Tc is to develop delta-doped (GaMn)As, which is confirmed by LSDA calculations. By studying the exchange interactions of the high Mn concentration systems, this high Tc case is explained by considering the ferromagnetic (FM) and anti-ferromagnetic (AFM) contribution of bands with different symmetries and the crystallographic dependence of exchange interactions.;First principles calculations are used to study the magnetic exchange interactions and Curie temperature (Tc) in III-V based diluted magnetic semiconductors and delta-doped layers. The local spin density approximation (LSDA) is combined with a linear-response technique to map the magnetic energy onto a Heisenberg hamiltonian, but no significant further approximations are made. |
