On the Nature of the Magnetism-Promoting States in Dilute Magnetic Semiconductor and Oxide Thin Films

Ferromagnetic (FM) ordering is observed in intermediate and wide gap dilute magnetic semiconductors as well as in oxides. While the interpretation of the experimental results is often clouded by the existence of non-homogeneous and non ideal nanostructures related to the fact that impurity concentration tends to far exceed the thermodynamic solubility limit, a general physical picture as to the physical origin of the FM interactions has emerged. We discuss the physical mechanism of ferromagnetism mediated by the carriers. We show that what stabilizes the FM spin arrangement is the energy-lowering due to interaction between partially occupied states in the band gap, localized on different transition atoms. These partially occupied states are hybrids between the d impurity band states and host vacancy orbitals, never host-like states as imagined in model Hamiltonian approaches. The theory uses both the model and first principle approach and can be applied to various types of systems such as dilute magnetic semiconductors [(Ga, Mn)As, (Ga, Mn)N, etc.] and oxides [(Ti, Co)O₂, (Zn, Mn)O, etc.] as well as nanodevices prepared of these materials.