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

TL;DR

This study investigates the magnetocaloric properties of Ni50Mn36In14, revealing its potential for magnetic refrigeration due to its sharp phase transformation, significant entropy change, and tunable relative cooling power through compositional adjustments.

Contribution

It introduces an improved calorimetry method for analyzing field-induced entropy changes and provides insights into optimizing the material's cooling performance.

Findings

Sharp martensitic transformation near 345 K

Large field-induced entropy change observed

Significant relative cooling power achievable through compositional tuning

Abstract

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