INTERACTION BETWEEN BAND ELECTRONS AND TRANSITION-METAL IONS IN DILUTED MAGNETIC SEMICONDUCTORS

We present a theoretical study of the effective exchange interaction arising from the hybridization between the valence-band states and the localized d orbitals of a transition-metal impurity in a II-VI semiconductor. The irreducible tensor method is used to deduce the effective Hamiltonian in the manifold of the ground multiplet of a 3d(n) ion in a tetrahedral crystal field. There is no coupling in the cases of Sc2+ and Ti2+ ions. For Mn2+, Fe2+, and Co2+ the coupling reduces to the usual spin-exchange Kondo Hamiltonian, in agreement with experiments; the observed increase of the exchange parameter \N0-beta\ from Mn to Fe to Co in a given host is also explained. In the cases of V2+, Cr2+, Ni2+, and Cu2+ additional coupling terms involving the orbital degrees of freedom are obtained; these predict drastic modifications of the valence-band splitting in a magnetic field.