Spin-polarized transport utilizing d⁰ ferromagnetism: an ab initio study of CaC/MgS/CaC (0 0 1) heterojunctions

The electronic structure and magnetic properties of rocksalt-type CaC compound are studied by means of first-principles calculations. The B1-type calcium monocarbide is a metastable, nearly half-metallic ferromagnetic compound, with a magnetic moment of 1.81 μ _B/f.u. and a negative Fermi level spin-polarization of 50%. The estimated Curie temperature exceeds the room temperature. The electronic, magnetic and spin-polarized transport properties of CaC/MgS/CaC (0 0 1) heterostructures are investigated by using a first-principles Green's function technique for layered structures in conjunction with the Kubo–Landauer formalism. The magnetism of CaC (0 0 1) electrodes is robust while the Fermi level spin-polarization of interfacial CaC layers at CaC/MgS (0 0 1) interfaces increases over the bulk value. The localized states formed at CaC/MgS (0 0 1) interfaces strongly enhance the minority-spin ferromagnetic state conductance. The current spin-polarization reaches values as high as 99%. Very large magnetoresistance ratios, above 10⁴%, are in evidence. The highly magnetoresistive effect observed for CaC/MgS/CaC (0 0 1) heterojunctions together with the robust ferromagnetism of CaC (0 0 1) electrodes make this system attractive in the context of spin-electronics. (paper)