Electronic structure and magnetism in half-Heusler compounds

In this paper we have applied the full-potential linearized muffin tin orbital method and the tight-binding linearized muffin tin orbital method to investigate in detail the electronic structure and magnetism of a series of half-Heusler compounds XMZ with X = Fe,Co,Ni, M = Ti,V,Nb,Zr,Cr,Mo,Mn and Z = Sb,Sn. Our detailed analysis of the electronic structure using various indicators of chemical bonding suggests that covalent hybridization of the higher-valent transition element X with the lower-valent transition element M is the key interaction responsible for the formation of the d–d gap in these systems. However, the presence of the sp-valent element is crucial to provide stability to these systems. The influence of the relative ordering of the atoms in the unit cell on the d–d gap is also investigated. We have also studied in detail some of these systems with more than 18 valence electrons which exhibit novel magnetic properties, namely half-metallic ferro- and ferrimagnetism. We show that the d–d gap in the paramagnetic state, the relatively large X–Sb hybridization and the large exchange splitting of the M atoms are responsible for the half-metallic property of some of these systems.