Abstract: A quantitative theoretical analysis of the heat capacity of metamagnetic shape memory alloy (MMSMA) is reported. It describes the peculiarities of the heat capacity of Ni-Mn-Sn alloy, which undergo a paramagnetic-ferromagnetic phase transition and a magnetostructural phase transformation (MPT) from ferromagnetic austenite to a weakly magnetic martensite. Good agreement between the experimental and theoretical temperature dependences of the heat capacity is observed. It is shown that the heat capacity of MMSMA can be presented as the sum of three terms: (i) a nonmagnetic term describing the heat capacity of crystal lattice, when the alloy temperature is well below the MPT temperature or above Curie temperature; (ii) a nonmagnetic term caused by the martensitic lattice distortion, which arises in the course of magnetostructural transformation; and (iii) a magnetic term related to the magnetic ordering of austenite and martensite. For Ni-Mn-Sn alloy, all terms appeared to be comparable in magnitude and, therefore, none of them can be ignored a priori. A similar behavior is expected for other MMSMAs.

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