Electronic Structure, Magnetic Properties and Martensitic Transformation of Ni50Mn36.5Sb13.5-xSix Alloys

A series of Ni50Mn36.5Sb13.5-xSix (x = 0 - 2.5) Heusler alloys was prepared. Effect of Si-doping on the formation, martensitic transformation and magnetic properties of Ni-Mn-Sb alloys was investigated experimentally and theoretically. The increasing Si content leads to the increase of the Curie temperature TC and decrease of the saturation magnetization Ms at 5K. The martensitic transformation temperature Tm also shows a decreasing tendency with the substitution of Si for Sb. First-principles calculations indicate that the martensite has a lower total energy comparing with the austenite, which supports the phase transition observed experimentally. The energy difference between the martensite and austenite Delta EM suggests that the martensitic transformation temperature TM will decrease with a small amount of Si-doping, but increase when Si content is high. This explains the decrease of TM observed in the experimental samples, for in these samples, the Si content is in the Delta EMdecreasing region. The calculated total spin moment of the martensite shows a decreasing tendency with increasing Si content, which agrees with the variation of saturation magnetization Ms at 5K.