The investigation of the phase transformations in the shape-memory Heusler Ni-Mn-X (In, Sn,Sb) alloys by Monte-Carlo simulations

The Heusler Ni-Mn-X (such X=In, Sb, Sn) alloys, which relate to the class of shape-memory alloys, attract much attention because they have also the giant magnetocaloric effect and the giant magnetoresistance. These properties are applicable in developing actuator materials and materials for magnetic refrigeration. The aim of this work is the theoretical description and the modeling magnetic properties in Ni-Mn-X (such X=In, Sb, Sn) alloys by the classical Monte Carlo method. In the proposed theoretical model for description of the phase transformation in Ni-Mn-X alloys the phase transitions from the mixed antiferromagnetic – ferromagnetic martensitic states to the ferromagnetic austenitic state and from ferromagnetic austenitic state to paramagnetic austenitic state are considered. The whole three – dimensional cubic lattice with periodic boundary conditions included the magnetostructural interaction between the magnetic and the structural subsystems. The magnetic part is described by the “q-state” Potts model with local interactions. The structural part is described by the degenerated three-state Blume-Emery-Griffiths model for the structural phase transformation. The configuration of antiferromagnetic clusters on the ferromagnetic lattice was set random and the clusters concentration was determined from experimental compositions of the Ni-Mn-X (X=In, Sb, Sn) alloys. By the help of theoretical model the temperature dependences of the normalized magnetization, strain order parameter, magnetic heat capacity and internal energy are obtained. All quantities are in good agreement with the available experimental data.