The project is devoted to the elaboration of theoretical model for the accounting of the spin-wave contribution to the thermodynamics characteristics of magnetocaloric alloys with magnetostructural phase transitions.It was considered previously that the low temperature specific heat of magnetic solid consists of two parts: electronic term and lattice contribution, which is described by Debye equation. The magnetic (spin-wave) contribution to the specific heat was considered negligibly small. However, the experimental researches showed that specific heat value measured for Ni-Mn-In alloys, being in antiferromagnetic martensitic phase, is significantly different from that measured for the alloys being in the ferromagnetic (FM) parent state [1]. Due to this the theoretical approach of the determination of magnetic part of the specific heat of ferromagnetic solid was proposed and applied to the number of non-stoichiometric Ni-Mn-In alloys [2]. It was shown that the disregard of magnetic contribution to the specific heat of FM solid results in the noticeable underestimation of Debye temperature and overestimation of the specific heat of electron subsystem of FM solid.

The aim of this project is to apply the elaborated theoretical approach to the different Heusler alloys to elucidate the spin-wave contribution to the low temperature specific heat of Heusler alloys. The evaluation of spin-wave contribution to specific heat of different Heusler alloys will allow to compute the real dependence of Debye temperature on chemical composition and to account the contribution of electron subsystem. The separation of different contribution to specific heat elucidates the role of magnetic ordering on the properties of alloys with magnetostructural phase transitions.

[1] R.Y. Umetsu, X. Xu, W. Ito, R. Kainuma, Metals 7, 414 (2017).

[2] A. Kosogor, V.A. L'vov, R.Y. Umetsu, X. Xu, R. Kainuma, J. Magn. Magn. Mater. 541, 168549 (2022).