Influence of Fe-doping on magnetic structure and martensitic transformation in NiMnIn and NiMnSb alloys

Influence of Fe substitution for Ni on the magnetic properties and martensitic transformation was investigated theoretically in Heusler alloys Ni2Mn1.5Z0.5 (Z = In, Sb). Fe-doping does not change the general magnetic structure of Ni2Mn1.5Z0.5. In both Ni2Mn15In0.5 and Ni1.75Fe0.25Mn1.5In0.5 the austenitic phase is ferromagnetic and martensitic phase is antiferromagnetic, which leads to the large ΔM observed experimentally. But in Ni2Mn1.5Sb0.5 and Ni1.75Fe0.25Mn1.5Sb0.5, the antiferromagnetic state is stable in both austenite and martensite. This difference is mainly related to the different atomic radii of In and Sb, which change the distance between Mn (B) and Mn (D). Parallel or antiparallel coupled Mn moments determine the magnetic properties of these alloys. But the partial moment of Fe is large and its direction reverses after martensitic transformation, which makes it a possible way to adjust the magnetic properties of MSMAs. Calculation also suggests that the substitution of Fe for Ni can lower the martensitic transition driving force and lead to the decrease of phase transition temperature. These results agree well with preceding experimental results and make reasonable explanation for them.