Site preference of Cu and its influence on martensitic transformation and magnetic properties of Heusler alloy Mn2NiGa0.5Cu0.5

Abstract

Rietveld refinement of Heusler alloys Mn₂NiGa_1-xCu_x (x = 0.1, 0.3 and 0.5) XRD patterns confirms that doping element Cu occupies both A and D site simultaneously. And a higher percentage of Cu tends to occupy the D site with increasing Cu content. To investigate the influence of Cu occupation on martensitic transformation and magnetism, first-principles calculations on Mn₂NiGa_0.5Cu_0.5 with different Cu occupation between A, D sites were performed. In Mn₂NiGa_0.5Cu_0.5 austenite, with more Cu occupying D site, the phase stability increases and equilibrium lattice constant decreases. Cu entering the D site can enhance antiferromagnetic coupling between Mn (B) and Mn (A) spin moment, which leads to a rapid decrease of total moment of the austenite. The martensite-austenite energy difference ΔE_M shows an increasing tendency with more Cu occupying the D site, which helps to improve the martensitic transformation temperature and can be explained by the electronic structure calculations.