Phase Transformation, Microstructure and Magnetocaloric Properties in Polycrystalline Bulk Ni$_{50}$Mn$_{50-{\rm z}}$Sn$_{\rm z}$ Alloys

Abstract

The martensitic and magnetic transformations in bulk Ni <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50</sub> Mn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50 - z</sub> Sn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z</sub> (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 = 11.5-15.0 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 aΔS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</sub> value 2.5 Jkg <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">- 1</sup> K <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">- 1</sup> at 273 K for z = 13.5 at % Sn-content.