Spin-polarized half-metallic state of a ferromagnetic δ layer in a semiconductor host

We discuss a model which is apt to describe the appearance of a spin-polarized half-metallic state around a single delta layer of a magnetic transition metal embedded into a nonmagnetic semiconductor host. We show that ferromagnetism in this system can be attributed to the intrinsic physical properties of the delta layer. The relevant physical effects described by our model are the hybridization of the electron states of the metal and semiconductor atoms, the charge redistribution around the delta layer, and the electron-electron correlation on a metal atom, which is the driving force of ferromagnetism. We obtain the mean-field phase diagram of the model at zero and finite temperature, both in the case when the chemical potential is fixed, and when the density of particles on the delta layer is fixed. The relevance of our results in connection with numerical and experimental results on the so-called digital magnetic heterostructures, in the absence and in the presence of a quantum-well carrier channel, is eventually discussed.