Ab initio calculations and synthesis of the off-stoichiometric half-Heusler phase Ni_(1-x)Mn_(1+x)SB

摘要

We perform a combined theoretical and experimental study of the phase stability and magnetism of the off-stoichiometric Ni_(1-x)Mn_(1+x)Sb 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 Ni_(1-x)Mn_(1+x)Sb over the whole composition range O≤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 MN_2Sb. Furthermore we find that half-Heusler Ni_(1-x)Mn_(1+x)Sb retains half-metallic band structure over the whole concentration range and that the magnetic moments of substitutional Mn_(ni) 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 Ni_(1-x)Mn_(1+x)Sb films on MgO substrates by means of magnetron sputtering.