Heat capacity of the Ni50Mn37(In0.2Sn0.8)13 alloy

Heat capacity of the Heusler-type Ni50Mn37(In0.2Sn0.8)(13) alloy has been studied in external magnetic fields up to 3 T. The alloy has the austenite Curie temperature T-CA approximate to 290 K, the martensitic phase transformation temperature T-M approximate to 220-240 K, and the martensite Curie temperature T-CM approximate to 185 K. The martensitic phase transition is accompanied by a considerable change of both magnetization and resistivity of the sample. It was found that upon the first-order martensitic transformation the heat capacity demonstrate hysteresis, both temperature and peak values being different. The maximum value of the heat capacity near T-M on cooling strongly differs from that on heating. In magnetic field the peaks of the heat capacity shift to lower temperatures with the rate Delta T-M/Delta B approximate to 2.5 K/T. The difference in the peak values of Delta C is caused by either overheating or overcooling the sample during the measurement of each point and the release of the latent heat of the martensitic phase transformation. The estimations of magnetocaloric effect (MCE) from the magnetic field effect on the heat capacity and direct measurements clearly demonstrate that the transition is accompained by a negative (MCE) at T-M. The hysteresis observed leads to a decrease of the (MCE) in magnetic refrigeration cycle.