Martensitic Transformation in Ni $_{50}$ Mn $_{50-{\rm x}}$ Sn

We report the study of structural and magnetic properties of Ni₅₀Mn_{50 - x}Sn_x(x = 11 and 12.5) and Ni₄₉Mn_{51 - x}Sn_x(x = 13) Heusler alloys in bulk and ribbon shape. Experimental results were obtained by differential scanning calorymetry, X-ray diffraction, and vibrating sample magnetometry techniques. The Ni-Mn-Sn system undergoes a martensitic structural transformation in a wide temperature range. For example, for Ni ₄₉Mn ₃₈Sn ₁₃, the start and finish temperatures of the martensitic phase transformation for bulk alloy were Ms = 288 K and Mf = 245 K, while the ones found for austenite were As = 261 K and Af = 304 K. The Curie temperature for the austenite was evaluated to be around 325 K. In the ribbon of same composition, the magnetization increases monotonically with the temperature showing an abrupt change in the slope at T = 258 K as a consequence of the martensite-austenite transformation. The complex behavior exhibited by these Heusler alloys should be ascribed to the strong coupling between magnetism and structure, being their magnetic behavior determined by the distance between Mn atoms.