Effect of site occupancy disorder on Martensitic properties of Mn${}_2$NiIn type alloys: x-ray absorption fine structure study

We have carried out $\mathit{\text{ab-initio}}$ calculations of local structure of Mn and Ni in Mn${}_2$Ni${}_{1.5}$In${}_{0.5}$ alloy with different site occupancies in order to understand the similarities in martensitic and magnetic properties of Mn${}_2$Ni${}_{1+x}$In${}_{1-x}$ and Ni${}_2$Mn${}_{1+x}$In${}_{1-x}$ alloys. Our results show that in Mn${}_2$Ni${}_{1+x}$In${}_{1-x}$ alloys there is a strong possibility of Mn atoms occupying all the three, X, Y and Z sites of X${}_2$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${}_2$Mn${}_{1+x}$In${}_{1-x}$ alloys. Further, a comparison of the calculations with experimental XAFS at the Mn and Ni K edges in Mn${}_{2-y}$Ni${}_{1.6+y}$In${}_{0.4}$ ($-0.08\le y\le 0.08$) indicate a strong connection between martensitic transformation and occupancy of Z sites by Mn atoms.