Half-metallic p-electron ferromagnetism in Ca and Sr pnictides

We investigated the magnetism in Ca and Sr pnictides by using the first-principles calculations. These compounds are half-metallic and ferromagnetic (FM) when they assume the zinc-blende structure at the equilibrium lattice constant. Ferromagnetism is induced by the spin polarization of the p-orbitals of the pnictogen atoms; Ca and Sr atoms have no magnetic moments, which is different from that of CrAs or CrSb with a zinc-blende structure. To confirm the mechanism of the ferromagnetism, we have calculated a hypothetical crystal - fcc-As with two additional electrons - and have shown that fcc-As has the same magnetic moment as CaAs with a zinc-blende structure. This means that the role of Ca or Sr atoms is to provide electrons with As atoms at the fee site and to sustain the distances between the As atoms and crystal symmetry. The FM exchange interactions between the pnictogen atoms are considered to exist in these lattices, which is briefly discussed.