Influence of solidification microstructure on the magnetic properties of Ni–Mn–Sn Heusler alloys

There have been many investigations to identify new alloys exhibiting large magnetic field-induced strain and more recently, the giant magnetocaloric effect. For any particular alloy system, it is necessary to adjust composition to alter the magnetic ordering and structural transformation temperatures to achieve the desired field-induced response. For the Ni–Mn–Sn alloy system, this compositional tuning has dramatic effects on microstructural development significantly affecting both transitions. Solidification induced chemical variations, when not fully equilibrated, have been found to mask the intrinsic magnetostructural behavior in Ni50Mn37Sn13. The use of a phase purity criterion was found to be an insufficient descriptor for determining homogeneity. When both structural and chemical homogenization are achieved, the nature and sequence of the transitions were found to be: (1) austenite paramagnetic to ferromagnetic transition, (2) coupled ferromagnetic austenite to paramagnetic martensite magnetostructural transition, and (3) paramagnetic to ferromagnetic martensite transition with Curie–Weiss behavior on heating above its Curie temperature.