Magnetic and magnetocaloric properies of Heusler alloys Ni-Mn-Sn with an excess of Mn within the theoretical and experimental approaches

This work is devoted to the theoretical and experimental study of the Heusler alloy Ni-Mn-Sn with almost equal Ni and Mn content. According to ab initio calculations, for Ni${}_{43.75}$Mn${}_{46.875}$Sn${}_{9.375}$ the energetically favorable structures of the austenite and martensite phases are regular Heusler structures L2$_1$ (Fm3m, No.   225) and L1$_0$ (Fmmm, No. 69)), which have different ferrimagnetic ordering of the Mn magnetic moments located at the Ni and Sn sublattices. Using the Potts — Blume — Emery — Griffiths Hamiltonian and the Monte Carlo method, the magnitude of the magnetocaloric effect is predicted $(\Delta S_{mag} \approx 1.3$ J/(kgK) and $T_{ad} \approx -0.6 K$) at the point of the magnetostructural transition upon the magnetic field change from 0 to 2 T. Concerning the experiment, the results of measuring the temperature dependences of the magnetization and the heat capacity for the Ni${}_{43}$Mn${}_{46}$Sn${}_{11}$ composition in various magnetic fields are presented. The change in the magnetization between the austenite and martensite phases across the martensitic transition is about 55 Am${}^2$/kg. An indirect estimate of the value $\Delta T_{ad}$ from the heat capacity measurements around the martensitic transformation region yields $\approx-0.5$ K upon the magnetic field change from 0 to 2 T.