# Effect of site occupancy disorder on Martensitic properties of Mn$_{2}$NiIn type alloys: x-ray absorption fine structure study

## TL;DR

This study uses ab-initio calculations and X-ray absorption data to explore how site occupancy disorder of Mn and Ni atoms influences the martensitic and magnetic properties of Mn-Ni-In alloys.

## Contribution

It reveals the specific site occupancy preferences of Mn and Ni atoms and links Mn occupancy of Z sites to martensitic transformation in these alloys.

## Key findings

- Mn atoms can occupy X, Y, and Z sites in the structure.
- Ni atoms preferentially occupy X sites.
- Mn occupancy of Z sites correlates with martensitic transformation.

## Abstract

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.