Ab initio calculations and synthesis of the off-stoichiometric half-Heusler phase $Ni1−xMn1+xSb$ Available to Purchase

We perform a combined theoretical and experimental study of the phase stability and magnetism of the off-stoichiometric $Ni1−xMn1+xSb$ in the half-Heusler crystal phase. Our work is motivated by the need for strategies to engineer the magnetism of potentially half-metallic materials, such as NiMnSb, for improved performance at elevated temperatures. By means of ab initio calculations we investigate $Ni1−xMn1+xSb$ over the whole composition range $0≤x≤1$ of Ni replacing Mn and show that at relevant temperatures, the half-Heusler phase should be thermodynamically stable up to at least $x=0.20$ with respect to the competing C38 structure of $Mn2Sb$⁠. Furthermore we find that half-Heusler $Ni1−xMn1+xSb$ retains half-metallic band structure over the whole concentration range and that the magnetic moments of substitutional $MnNi$ atoms display magnetic exchange interactions an order of magnitude larger than the Ni–Mn interaction in NiMnSb. We also demonstrate experimentally that the alloys indeed can be created by synthesizing off-stoichiometric $Ni1−xMn1+xSb$ films on MgO substrates by means of magnetron sputtering.