Magnetic properties, martensitic and magnetostructural transformations of ferromagnetic Ni–Mn–Sn–Cu shape memory alloys

The influence of Cu doping on structural and magnetic properties of Ni50−xMn36Sn14−yCux,y (x = 0, 1, 2 and y = 1 at.%) ribbons produced by melt spinning has been investigated. The crystalline structures of the alloys were determined by X-ray diffraction (XRD) patterns analysis XRD measurements. Cu addition in specific sites shifts structural transition temperatures. The L21 austenite is found for x = 0, 1 and 2 and modulated martensitic structure for y = 1. Characteristic transformation temperatures were obtained from differential scanning calorimetry scans. It is found that the addition of Cu for Ni stabilizes the austenite phase (increasing martensitic start temperature from 194 to 228 K), whereas replacing small amounts of Cu for Sn stabilizes the modulated martensite phase (increasing martensitic transformation temperature from 194 to 325 K). The transformation temperatures generally increases as the Cu content increases. Therefore, the magnetostructural transition, analysed by vibrating sample magnetometry, is tuned by appropriate Cu doping in the alloys. Likewise, both martensitic and austenitic states exhibit ferromagnetic behaviour.