Direct Measure of Giant Magnetocaloric Entropy Contributions in Ni-Mn-In

Abstract

Off-stoichiometric alloys based on Ni2MnIn have drawn attention due to the coupled first order magnetic and structural transformations, and the large magnetocaloric entropy associated with the transformations. Here we describe calorimetric and magnetic studies of four compositions. The results provide a direct measure of entropy change contributions at low temperatures as well as at the first-order phase transitions. Thereby we determine the maximum possible field-induced entropy change corresponding to the giant magnetocaloric effect. We find a large excess entropy change above that of the magnetic moments, but only in compositions with no ferromagnetic order in the high-temperature austenite phase. Furthermore, a molecular field model corresponding to magnetic order in the low-temperature phases is in good agreement, giving an entropy contribution nearly independent of composition, despite significant differences in overall magnetic response of these materials.