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

Abstract

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.