Electronic structure and magnetism in doped semiconducting half-Heusler compounds

We have studied in detail the electronic structure and magnetism in M (Mn and Cr)-doped semiconducting half-Heusler compounds FeVSb, CoTiSb and NiTiSn (XYxM1−xZ) in a wide concentration range using the local-spin density functional method in the framework of the tight-binding linearized muffin tin orbital method (TB-LMTO) and supercell approach. Our calculations indicate that some of these compounds are not only ferromagnetic but also half-metallic and may be useful for spintronics applications. The electronic structure of the doped systems is analysed with the aid of a simple model where we have considered the interaction between the dopant transition metal (M) and the valence band X–Z hybrid. We have shown that the strong X-d–M-d interaction places the M-d states close to the Fermi level with the M-t2g states lying higher in energy in comparison to the M-eg states. Depending on the number of available d electrons, ferromagnetism is realized provided that the d manifold is partially occupied. The tendencies toward ferromagnetic (FM) or antiferromagnetic (AFM) behaviour are discussed within Anderson–Hasegawa models of super-exchange and double-exchange. In our calculations for Mn-doped NiTiSn, the strong preference for FM over AFM ordering suggests a possible high Curie temperature for these systems.