We have carried out \textit{ 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.
Categories: cond-mat.mtrl-sci