Magnetic and structural properties of IIA-V nitrides

Electronic, magnetic, and structural properties of several IIA-V compounds are analyzed using ab initio calculations. We consider four crystal structures: zinc-blende, NiAs, rocksalt, and Zn3P2. Our results indicate that IIA-V nitrides in the rocksalt phase are stable ferromagnetic half-metals characterized by the total spin polarization of free holes in the valence band. The previously considered zinc-blende phase of II-V crystals is ferromagnetic as well, but is less stable by about 0.3 eV/atom. The stability of the Zn3P2 phase is close to that of the rocksalt, but the spin polarization vanishes in this case. Analysis of the electronic structure shows that ferromagnetism of IIA-V compounds originates in the spin polarization of the p shell of anions, as described by Hund's rule, which persists in solids after formation of bonds. Furthermore, the results for isolated atoms indicate why the spin polarization is the most stable in IIA-V nitrides, which are discussed in detail.