Magnetic properties and possible martensitic transformation in Mn2NiSi and Ni2MnSi Heusler alloys

The magnetic properties and electronic structure of Mn2NiSi and Ni2MnSi Heusler alloys have been studied by using the first-principles. The possible non-modulated martensitic transformations in Mn2NiSi and Ni2MnSi alloys have been investigated. In both austenitic and martensitic phases, Mn2NiSi is a ferrimagnet. The antiparallel alignment of Mn (A) and Mn (B) moments is found. In martensitic Mn2NiSi, the global energy minimum occurs at c/a=1.37 with 1% decrease of the martensitic cell volume. The energy difference ΔE between the austenitic and martensitic phases is 400 meV/cell, so it is more likely to realize martensitic transformation for Mn2NiSi alloy. Unlike Mn2NiSi alloy, the global energy minimum occurs at c/a=1.02 without cell volume change in martensitic Ni2MnSi. But the energy difference ΔE between the austenitic and martensitic phases is only 0.3 meV/cell. Meanwhile, around c/a=1 an anomaly is observed in the Etot-c/a curve which is related to a very slightly martensitic distortion trend in Ni2MnSi.