Ion irradiation induced modifications of nanostructured Ni–Mn–Sn ferromagnetic shape memory alloy thin films

Thin films of Ni–Mn–Sn ferromagnetic shape memory alloy, grown on Si substrate by DC magnetron sputtering were bombarded by 450 keV Ar+ 4 ions at different fluences ranging from 1 × 1014 to 3 × 1016 ions/cm2 in order to investigate the effect of ion irradiation on characteristic transformation temperatures and thus on shape memory behavior. Temperature dependent resistivity measurements reveal the increase in martensitic transformation temperature (~ 100 K) upto a fluence of 1 × 1015 ions/cm2, above which shape memory behavior degrades and completely loses its behavior at 3 × 1016 ions/cm2, which is ascribed to the amorphization of Ni–Mn–Sn structure at a fluence of 3 × 1016 ions/cm2 as evidenced from X-ray diffraction pattern. The diffuse rings in the electron diffraction pattern also confirmed the amorphization of the film at highest fluence. The temperature dependent magnetization measurements also show the increase in martensitic transformation temperature upto a fluence of 1 × 1015 ions/cm2 in support of resistivity data. This work gives a possibility to acquire a better control on the properties of FSMA thin films using ion irradiation.