Microstructure characterization, structure and magnetic properties of Ni-Mn-Sn shape memory alloys

In this study, three shape memory alloys, Mn50Ni50-xSnx (x = 5, 7.5, and 10), were elaborated by melt spinning. The structure, microstructure, and magnetic properties of these alloys were carried out by X-ray diffraction, scanning electron microscopy, and physical property measurement system, respectively. The experimental results showed that the increase in Sn ratio caused a phase transformation. The structure of the martensite phase (for x = 5 and 7.5) was seen as a monoclinic 14 M structure, while the structure of the austenite phase (for x = 10) was observed as a cubic L2(1) structure. We revealed that the addition of Sn led to an almost linear decrease in martensitic transition temperatures, due to the decrease in valence electron ratio (e/a). We explored that for x = 10, the martensitic transition that occurs from the ferromagnetic austenite to weakly magnetic martensite was realized due to the strong magnetostructural coupling in this alloy. Also, it is found that there is a slight decrease in temperatures and a slight increase in the thermal hysteresis range, due to the increase in the magnetic field. While, for x = 7.5 and x = 5, they have the transitions at high temperatures above 400 and 550 K, respectively. This fact might limit these alloys in their applications. So, the present results indicate that the amount of Sn content in the MnNiSn alloys plays an important role to modify the structural and magnetic properties.