Exchange in II-VI-based magnetic semiconductors (invited)

We present a physically oriented survey of exchange constants among Mn local moments, and between Mn moments and sp band electrons in II-VI-based magnetic semiconductors (MS) such as Cd1−xMnxTe. A simple three-site model illustrates the physical principles underlying our quantitative calculations of Mn-Mn exchange based on a semiempirical tight-binding Anderson model. Superexchange interactions, computed perturbatively in the Mn d-sp band hybridization, are the dominant mechanisms of isotropic and anisotropic Mn-Mn exchange. The Dzyaloshinsky–Moriya (DM) anisotropic superexchange constant D has a magnitude of ∼5% of the isotropic superexchange constant J. The DM exchange explains spin resonance linewidths and the nature of short range spin ordering in the magnetically concentrated regime. The contribution of anistropic Mn-sp band exchange is also considered.