The non-stoichiometric Heusler alloy Ni 50Mn36In14 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.
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