Calorimetric and magnetic study for Ni$_{50}$Mn$_{36}$In$_{14}$ and relative cooling power in paramagnetic inverse magnetocaloric systems

摘要

The non-stoichiometric Heusler alloy Ni$_{50}$Mn$_{36}$In$_{14}$ undergoes amartensitic phase transformation in the vicinity of 345 K, with the hightemperature austenite phase exhibiting paramagnetic rather than ferromagneticbehavior, as shown in similar alloys with lower-temperature transformations.Suitably prepared samples are shown to exhibit a sharp transformation, arelatively small thermal hysteresis, and a large field-induced entropy change.We analyzed the magnetocaloric behavior both through magnetization and directfield-dependent calorimetry measurements. For measurements passing through thefirst-order transformation, an improved method for heat-pulse relaxationcalorimetry was designed. The results provide a firm basis for the analyticevaluation of field-induced entropy changes in related materials. An analysisof the relative cooling power (RCP), based on the integrated field-inducedentropy change and magnetizing behavior of the Mn spin system withferromagnetic correlations, shows that a significant RCP may be obtained inthese materials by tuning the magnetic and structural transformationtemperatures through minor compositional changes or local order changes.