Theoretical prediction of the giant magnetocaloric effect in Ni40Co10Mn40Sn7Al3 Heusler alloy.

By using ab initio calculations and Monte Carlo simulations, the influence of the small amount of Al on magnetic and magnetocaloric properties of Ni-Co-Mn-Sn Heusler alloy is studied. First-principles calculations have shown that addition of Al leads to an increase in the energy difference between ferromagnetically (FM) ordered austenite and ferrimagnetically (FIM) ordered martensite. The observed tendency points to an increase in the martensitic transformation temperature (Tm) in accordance with the relation ?E ~ kBTm. The calculated exchange coupling constants, especially for martensite, exhibit the longrange oscillation behavior showing the strong competition between ferromagnetic and antiferromagnetic interactions. By the help of the Hamiltonian model (Potts-Blume-Emery-Griffiths), the temperature dependences of the magnetization, tetragonal deformation, and adiabatic temperature changes for magnetic field variation are obtained. It is shown that the addition of few percent of Al into Ni-Co-Mn-Al leads to increase of the inverse magnetocaloric effect.