Effect of Sm-doping on the morphology and magnetic properties of radio frequency magnetron sputtered Ni-Mn-Ga films

Ni_55.5Mn₂₁Ga_23.5 and Ni₅₄Mn₂₂Ga₂₃Sm₁ films were prepared by radio frequency (RF) magnetron sputtering. The effect of Sm dopant on the morphologic and magnetic properties of Ni_55.5Mn₂₁Ga_23.5 films was investigated. Sm doping can refine the particle size of the films from 100 to 60 nm, and further grain growth is not occurs even after annealing at 1073 K for 3.6 ks. Compared to Ni_55.5Mn₂₁Ga_23.5 films, Sm-doped Ni₅₄Mn₂₂Ga₂₃Sm₁ films are easier to be magnetized and have a lower martensitic transformation temperature. In addition, the Curie temperature can also be adjusted, decreasing from 350 to 325 K after Sm doping. Martensitic transformation is not observed in the Sm-free films, which is close to the Curie temperature in the Sm-doped films, giving rise to the overlap of the structural and magnetic transition temperatures.