Electronic Structure of Half-metallic Magnets

We have analyzed the electronic structure of half-metallic magnets based on first principles electronic structure calculations of a series of semi-Heusler alloys. The characteristic feature of the electronic structure of semi-Heusler systems is a d-d gap in the density of states lying at/close to the Fermi level depending on the number of valence electrons. We have employed various indicators of chemical bonding to understand the origin of the gap in these systems, which is crucial for their half-metallic property. The density of states of other half-metallic magnets also supports a gap and it is a generic feature of these systems. We have discussed in some details the origin of magnetism, in particular, how the presence of the gap is crucial to stabilize half-metallic ferro and ferri magnetism in these systems. Finally, we have studied the role of magnetic impurities in semiconducting semi-Heusler systems. We show with the aid of model supercell calculations that these systems are not only ferromagnetic but also half-metallic with possibly high Curie temperature.