Half-metallic ferromagnetism in zinc-blende CaC, SrC, and BaC from first principles

Using the first-principles full-potential linearized augmented plane-wave method based on density functional theory, we have investigated the electronic structure and magnetism of hypothetical MC (M=Mg, Ca, Sr, and Ba) compounds with the zinc-blende (ZB) crystal structure. It is shown that ZB CaC, SrC, and BaC are half-metallic ferromagnets with large half-metallic gaps (up to 0.83 eV). The half metallicity is found to be robust with respect to the lattice compression and is maintained up to the lattice-constant contraction of 14%, 13%, and 9% for CaC, SrC, and BaC, respectively. The exchange interactions in these compounds are studied using the augmented spherical wave method in conjunction with the frozen-magnon approach. The Curie temperature is estimated within both the mean field approximation and the random phase approximation. The predicted Curie temperatures of all three half-metallic compounds considerably exceed the room temperature. The large half-metallic gaps, the robustness of the half metallicity with respect to the lattice contraction, and the high Curie temperatures make these systems interesting candidates for applications in spintronic devices. The absence of the transition-metal atoms makes these compounds important model systems for the study of the origin and properties of the half-metallic ferromagnetism of s-p electron systems.