Role of correlation and exchange for quasiparticle spectra of magnetic and diluted magnetic semiconductors

Theoretical foundation and applications of the generalized spin-fermion (sp-d) exchange lattice model to various magnetic systems, e.g., rare-earth metals and compounds, and magnetic semiconductors are discussed. The capabilities of the model to describe spin quasiparticle spectra are investigated. The main emphasis is put on the dynamic behavior of two interacting subsystems, the localized spins and spin density of itinerant carriers. A nonperturbative many-body approach is used to describe the quasiparticle dynamics. Scattering states are investigated and three branches of magnetic excitations are calculated in the regime characteristic of a magnetic semiconductor. For a simplified version of the model (Kondo lattice model) we study the spectra of quasiparticle excitations with special attention given to diluted magnetic semiconductors in a simple approximation to demonstrate the role of disorder effects. For this, to include the effects of disorder, a modified mean field is determined self-consistently. The approach permits to investigate and clarify the role of various interactions and disorder effects in unified and coherent fashion.