Mechanisms of exchange interactions between carriers and Mn or Eu spins in lead chalcogenides

A microscopic tight-binding model of the spin-dependent coupling between effective-mass electrons and localized spins in the IV-VI diluted magnetic semiconductors is proposed. Contributions from the direct Coulomb exchange as well as from the hybridization between band states and resonant levels associated with magnetic ions are taken into consideration. The exchange integrals are evaluated quantitatively and are shown to compare favorably with experimental values for both the Mn- and the Eu-based compounds. Some peculiarities of IV-VI magnetic alloys, which may render the virtual-crystal approximation invalid, are noted and linked to the previously unexplained experimental results.