The Effect of Anti-Site Disorder on Structural and Magnetic Properties of Ni-Co-Mn-In Alloys: Ab Initio and Monte Carlo Studies

In this paper, we report on the effect of partial structural B2-like disorder on martensitic transformation and thermomagnetization curves in Ni-Co-Mn-In alloy by using the theoretical approach involving first principles and Monte Carlo methods. In case of ground-state electronic calculations, the off-stoichiometric composition was treated by using both supercell and coherent potential approaches. It is found that the increase of a structural disorder degree leads to decrease the energy difference between austenite and martensite phases, which corresponds to a decrease in the martensitic transformation temperature according to \Delta E \approx k_{B}T_{m} . Besides, the magnetic exchange interaction constants for both martensite and austenite are slightly weakened by influence of structural disorder. Using calculated exchange coupling constants in the effective Potts-Blume-Emery-Griffiths Hamiltonian, a set of magnetization curves for the studied system is simulated. It is shown that the account of disorder results in a decrease in the magnetization value around the magnetostructural transformation. Theoretical results reproduce well the experimental ones.