Effect of site occupancy disorder on martensitic properties of Mn2NiIn type alloys: X-ray absorption fine structure study

Abstract

We have carried out ab-initio calculations of the local structure of Mn and Ni in the Mn sub(2)Ni sub(1.5)In sub(0.5) alloy with different site occupancies in order to understand the similarities in martensitic and magnetic properties of Mn sub(2)Ni sub(1+x)In sub(1-x) and Ni sub(2)Mn sub(1+x)In sub(1-x) alloys. Our results show that in Mn sub(2)Ni sub(1+x)In sub(1-x) alloys, there is a strong possibility of Mn atoms occupying all the three X, Y, and Z sites of the X sub(2)YZ Heusler structure, while Ni atoms preferentially occupy the X sites. Such a site occupancy disorder of Mn atoms is in addition to a local structural disorder due to size differences between Mn and In atoms, which is also present in Ni sub(2)Mn sub(1+x)In sub(1-x) alloys. Further, a comparison of the calculations with experimental x-ray absorption fine structure at the Mn and Ni K edges in Mn sub(2−y)Ni sub(1.6+y)In sub(0.4) (-0.08 less than or equal to y less than or equal to 0.08) indicates a strong connection between martensitic transformation and occupancy of Z sites by Mn atoms.