First-principles study of Pt doping effects on Ni2MnGa and Ni2FeGa ferromagnetic shape memory alloys

The influence of Pt doping on the lattice structure, magnetism, elastic moduli, and martensite transition of Ni2MnGa and Ni2FeGa Heusler alloys was studied using first-principles calculations. We investigated Pt substitution at all three different sites of Ni, Mn (Fe), and Ga with different concentrations. Partial Pt substitution at the Ni and Ga sites appeared to strengthen the ferromagnetism of these two alloys, whereas increasing the Pt content at the Mn (Fe) site weakened the total magnetic moment significantly. Pt doping at the three sites was conducive to austenite-martensite transformation, and the martensitic transition temperature T-M increased with increasing Pt concentration, especially for the replacement of Ga by Pt. Most Pt-doped Ni2MnGa and Ni2FeGa alloys follow the general rule regarding the tetragonal shear modulus C ' and T-M: a softening of C ' corresponds to an increase of T-M. Unlike the case of Pt occupation at the Ga site, substantial Pt substitution at the Ni and Mn (Fe) sites led to a remarkable decrease in the inherent brittleness of Ni2MnGa and Ni2FeGa and thus promoted their technological application.