Systematic understanding of half-metallicity of ternary compounds in Heusler and Inverse Heusler structures with 3d and 4d elements

Employing ab initio electronic structure calculations, we extensively study ternary Heusler compounds with the chemical formula X₂X′Z, where X = Mn, Fe or Co; Z = Al or Si; and X′ changes along the row of 4d transition metals. A comprehensive overview of these compounds, addressing the trends in structural, electronic, magnetic properties and Curie temperature, is presented here along with the search for new materials for spintronics applications. A simple picture of hybridization of the d-orbitals of the neighboring atoms is used to explain the origin of the half-metallic gap in these compounds. We show that arrangements of the magnetic atoms in different Heusler lattices are largely responsible for the interatomic exchange interactions that are correlated with the features in their electronic structures as well as the possibility of half-metallicity. We find seven half-metallic magnets with 100% spin polarization. We identify a few other compounds with high spin polarization as 'near half-metals' which could be of potential use in applications as well. We find that the major features in the electronic structures remain intact if a 3d X^′ constituent is replaced with an isoelectronic 4d, implying that the total number of valence electrons can be used as a predictor of half-metallic nature in compounds from the Heusler family. (paper)