Ab initio calculations of martensitic phase behavior in Ni2FeGa magnetic shape memory alloys

Abstract

A series of spin polarized energy calculations based on density functional theory (DFT) have been carried out to investigate the structural, magnetic, electronic and mechanical properties of Ni2FeGa magnetic shape memory alloys (MSMA's) in the austenitic and martensitic structures. We report that L2(1) austenitic phase is metastable at a = 5.76 angstrom the NM tetragonal and 5M monoclinic martensitic structures are stable at c/a = 1.33 and c/a = 0.99, respectively. That the electron removes from Ni to Fe site during phase transformation to martensite is confirmed by the increment in the magnetic moment of Ni, while decrement in that of Fe. The analysis of the partial density of states show that some distinguishable differences in the minority spin states occur upon martensitic phase transformation, such as, the replacement of the Fe states (e(g) and t(2g)) above Fermi level by only Fe-t(2g) states during L2(1)-5M transformation and the splitting of Fe-t(2g) states near Fermi level during 5M-NM transformation (through 7M). These changes lower the energy of the system, indicating that the final structure becomes stable. The soft tetragonal shear constant C' of the austenitic phase designates the ease of the phase transition into martensitic phase. It is shown that the results calculated in this study are in good agreement with the previous calculations and the available experiments