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

• L21, NM and 5M phases have the energy minimum at a = 5.76 Å, c/a = 1.33 and c/a = 0.99.
• Decrement in moment of Ni and increment in that of Fe reflect electrons transfer.
• Differences in minority DOS over MT lead to stabilize the final structure.
• C' taking small value in L21 leads to elastic instability in MT.

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 L21 austenitic phase is metastable at a = 5.76 Å, 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 (eg and t2g) above Fermi level by only Fe-t2g states during L21-5M transformation and the splitting of Fe-t2g 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.