Phase Transformation, Microstructure and Magnetocaloric Properties in Polycrystalline Bulk Ni50Mn50-zSnz Alloys

The martensitic and magnetic transformations in bulk Ni50Mn50-zSnz (z = 11.5-15.0) Heusler alloys were investigated by differential scanning calorimetry measurement and the vibrating sample magnetometry technique and are described in correlation to the microstructure. It is established that increasing the Sn-content in this series leads to change the alloy microstructure very sensitively from a martensite phase (with distinct martensite strips) over z = 11.5-13.5 to the austenite phase as early as z = 15.0 at room temperature. The structural transition temperature has decreased from 411 K for z = 11.5 at% of the Sn content to a value as low as 196 K for z = 15.0 at% Sn content. An inverse magnetocaloric effect (MCE) has been observed with a Delta S-M value 2.5 Jkg(-1) K-1 at 273 K for z = 13.5 at % Sn-content.