Half-metallic property of the bulk and (001) surfaces of MNaCs (M = P, As) half-Heusler alloys: A density functional theory approach

The structural, electronic and half-metallic properties of bulk and (001) surfaces of MNaCs (M = P, As) halfHeusler alloys are investigated. The half-metallic property have been observed in both of these materials. The spin-flip gaps of PNaCs and AsNaCs are found to be 0.25 and 0.21 eV, and the Curie temperatures are estimated to be 478.24 and 474.07 K within the mean field approximation, respectively. The mechanisms of half-metallicity in these materials are studied by considering the spin-dependent band structures and the atomic density of states. The preservation of the half-metallic ferromagnetism under stress are also investigated. The symmetric slab model is employed for the investigation of the (001) surfaces of the compounds because the electron spin polarization at the bulk of the materials does not guarantee the spin-polarization at the surfaces of them. It turns out that the half-metallic ferromagnetism is well preserved for P (As)-terminated surfaces, but it is removed at the NaCs-terminated surfaces of both of the compounds.