Effects of Bi-doping on electronic structure and martensitic transformation in Ni2MnGa and Mn2NiGa MSMAs: A theoretical approach

• Effect of Bi-doping on martensitic transformation in Heusler type MSMAs was investigated. • Bi-doping can suppress the martenstic transformation in Ni 2 MnGa 1-x Bi x and Mn 2 NiGa 1-x Bi x. • Electron density can be an appropriate factor to ascribe variation of martensitic transformation temperature. • Magnetic structures of Ni 2 MnGa and Mn 2 NiGa remain unchanged after Bi-doping. The effects of Bi-doping on the electronic structure, martensitic transformation and magnetic properties of Heusler alloys Ni 2 MnGa 1- x Bi x and Mn 2 NiGa 1- x Bi x ( x = 0, 0.25, 0.5, 0.75, 1) were investigated theoretically. The substitution of Bi for Ga has a negative effect on the martensitic transformation. The total energy difference ΔE M between the martensite and austenite decreases gradually with the doping of Bi. When x = 0.5, 0.75 and 1.0 in Ni 2 MnGa 1- x Bi x and x = 1.0 in Mn 2 NiGa 1- x Bi x , the martensite phase becomes higher in energy comparing with the austenite. Thus the doping of Bi can lower the martensitic transformation temperature T M and finally suppresses it. The possible reasons for this trend are related to the increasing valence electron concentration e/a and cell volume V with Bi-doping. The competition between them may be ascribed further by the electron density, which combines the effect of valence electron concentration and size effect. The electron densities of Ni 2 MnGa 1- x Bi x and Mn 2 NiGa 1- x Bi x decrease monotonously with increasing Bi content. This agrees well with the variation of ΔE M or T M . The doping of Bi does not change the magnetic structure of Ni 2 MnGa 1- x Bi x and Mn 2 NiGa 1- x Bi x . The former is ferromagnetic and the latter is ferrimagnetic in both martensite and austenite state. These results can help to introduce new component like Bi to Heusler alloys and discover new functional materials in them.