Effect of site occupancy disorder on martensitic properties of Mn_2Niln type alloys: X-ray absorption fine structure study

摘要

We have carried out ab-initio calculations of the local structure of Mn and Ni in the Mn_2Ni_(1.5)In_(0.5) alloy with different site occupancies in order to understand the similarities in martensitic and magnetic properties of Mn_2Ni_(1+x)In_(1_x): and Ni_2Mn_(1+x)In_(1_x) alloys. Our results show that in Mn_2Ni_(1+x)In_1 alloys, there is a strong possibility of Mn atoms occupying all the three X, Y, and Z sites of the X_2YZ 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_2Mn_ (1+x), Jn_(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_(2-y)Ni_(1.6+y),Ino.4 (-0.08 ≤ y ≤ 0.08) indicates a strong connection between martensitic transformation and occupancy of Z sites by Mn atoms.