Searching for hexagonal analogues of the half-metallic half-Heusler XYZ compounds

Abstract

The XYZ half-Heusler crystal structure can conveniently be described as a tetrahedral zinc blende YZ structure which is stuffed by a slightly ionic X species. This description is well suited to understand the electronic structure of semiconducting 8-electron compounds such as LiAlSi (formulated Li${}^{+}$[AlSi]${}^{-}$) or semiconducting 18-electron compounds such as TiCoSb (formulated Ti${}^{4+}$[CoSb]${}^{4-}$). The basis for this is that [AlSi]${}^{-}$ (with the same electron count as Si${}_2$) and [CoSb]${}^{4-}$ (the same electron count as GaSb), are both structurally and electronically, zinc-blende semiconductors. The electronic structure of half-metallic ferromagnets in this structure type can then be described as semiconductors with stuffing magnetic ions which have a local moment: For example, 22 electron MnNiSb can be written Mn${}^{3+}$[NiSb]${}^{3-}$. The tendency in the 18 electron compound for a semiconducting gap -- believed to arise from strong covalency -- is carried over in MnNiSb to a tendency for a gap in one spin direction. Here we similarly propose the systematic examination of 18-electron hexagonal compounds for semiconducting gaps; these would be the "stuffed wurtzite" analogues of the "stuffed zinc blende" half-Heusler compounds. These semiconductors could then serve as the basis for possibly new families of half-metallic compounds, attained through appropriate replacement of non-magnetic ions by magnetic ones. These semiconductors and semimetals with tunable charge carrier concentrations could also be interesting in the context of magnetoresistive and thermoelectric materials.

11 pages, 6 figures, of which 4 are colour

References in corpus (2)

• Covalent bonding and the nature of band gaps in some half-Heusler compounds
• An experimental and computational investigation of structure and magnetism in pyrite Co${}_{1-x}$Fe${}_x$S${}_2$: Chemical bonding and half-metallicity