Ab initio study of tetragonal variants in Ni2MnGa alloy

Abstract

A major challenge for the study of the magnetically shape-controlled memory alloys Ni-Mn-Ga is the structural search for their variants. We report studies of the variants of Ni2MnGa alloys from a theoretical point of view by means of density functional calculations using the generalized gradient approximation. The effect of tetragonal distortions is studied, and a metastable structure is found for c/a = 0.94, in agreement with experiments. The c/a<1 minimum is reinforced by considering volume expansions around the experimental values for several variants. After distortion, the electron density is redistributed around the Ni atoms as shown by neutron scattering experiments. The previous disagreement between the theoretical spin density and the experimental neutron scattering is explained. In addition, elastic constants and x-ray absorption spectra are calculated in order to encourage measurements of these quantities.