Magnetocaloric effect in Ni-Co-Mn-(Sn, Al) Heusler alloys: Theoretical study

The crystal structure, magnetic and magnetocaloric properties of Co-doped Ni-Mn-(Sn, Al) Heusler alloys were calculated using ab initio zero-temperature calculations combined with Monte Carlo finite-temperature simulations. To find the stable magnetic ground state for austenite and martensite, the calculations for ferromagnetic and ferrimagnetic orderings were carried out. Once accurate lattice constants were calculated, magnetic moments, exchange coupling constants, bulk moduli, Debye temperatures for the alloys studied were determined. Using the thermodynamic approach jointly with Monte Carlo simulations, martensitic phase transition temperatures were obtained from intersection of the Free energy curves. Finally, the temperature dependences of magnetic and magnetocaloric properties for the studied systems were simulated by the effective Potts-Blume-Emmery-Griffiths Hamiltonian. The obtained results are in a good agreement with available experimental data.