A deviation from the Arrhenius law in α-Fe self-diffusion and also in the diffusion of substitutional impurities was found experimentally. Below the Curie temperature the diffusion coefficients have lower values than those extrapolated from the paramagnetic region and the Arrhenius plot showed an upward curvature. Here, an attempt was made to understand this behaviour using first-principles calculations. Formation and migration energies for self-diffusion and also for the diffusion of some substitutional impurities were calculated. Spin-polarized and non-spin-polarized calculations were assumed to approximately represent ferromagnetic and paramagnetic α-Fe respectively. The calculations were performed using the WIEN97 code, with a super-cell of 36 atoms which permitted the inclusion of both vacancies and impurities and therefore the study of migration along the <111> direction. The increment in the diffusion barrier due to the total magnetic alignment at 0K, with respect to the paramagnetic case, was almost constant for non-magnetic impurities, as it was in experiments. For magnetic impurities, it depended upon the diffusing atom.

Ab initio Study of Magnetic Effects on Diffusion in α-Fe. R.A.Pérez, M.Weissmann: Journal of Physics - Condensed Matter, 2004, 16[39], 7033-43