Ab initio study of magnetic effects on diffusion inα-Fe

Abstract

A deviation from the Arrhenius law inα-Fe self-diffusion and also in the diffusion of substitutional impurities is foundexperimentally. Below the Curie temperature the diffusion coefficients have lower valuesthan those extrapolated from the paramagnetic region and the Arrhenius plot shows anupward curvature.In this work we attempt to understand this behaviour from first-principles calculations.Formation and migration energies for self-diffusion and also for the diffusion of somesubstitutional impurities are calculated. Spin-polarized and non-spin-polarizedcalculations are assumed to approximately represent ferromagnetic and paramagneticα-Fe respectively.The calculations were performed using the WIEN97 code, with a supercell of 36 atomswhich allows us to include both vacancies and impurities and therefore to study themigration along the direction. The increment in the diffusion barrier due to the total magnetic alignment at0 K, with respect to the paramagnetic case, is almost constant for non-magnetic impurities,as it is in the experiments, whereas for magnetic impurities it depends on the diffusingatom.