Structure and properties of CoMnSb in the context of half-metallic ferromagnetism

Although its X-ray powder diffraction patterns show a superstructure, the compound CoMnSb, like the well-known half-Heusler alloy NiMnSb, is often referred to the category of half-metallic ferromagnets with C1(b) structure. Our study assigns CoMnSb to space group Fm (3) over barm. The crystal structure of CoMnSb can be represented as an alternation of Co2MnSb and MnSb structural units, and, in contrast to NiMnSb, displays three Mn and two Sb positions in the elementary cell. The presence of nonequivalent antimony and manganese positions was verified using NMR and Mossbauer spectroscopic measurements. Band-structure calculations based on a proposed structure confirm the experimentally found magnetic moment value of approximately 4 mu(B)/f.u. and demonstrate that CoMnSb is not a half-metallic ferromagnet.