A deviation from the Arrhenius law, for self-diffusion and for the diffusion of substitutional impurities in the α-phase, was found experimentally. Below the Curie temperature, the diffusion coefficients had lower values than those extrapolated from the paramagnetic region; and the Arrhenius plot exhibited an upward curvature. First-principles calculations were used to analyze this behavior. The formation and migration energies for self-diffusion, and for the diffusion of some substitutional impurities, were calculated. Spin-polarized and non spin-polarized calculations were assumed to approximate to ferromagnetic and paramagnetic α-Fe, respectively. The calculations were performed using a super-cell of 36 atoms. This permitted the inclusion of vacancies and impurities, and therefore the study of migration along the <111> direction. The increment in the diffusion barrier, due to total magnetic alignment at 0K (with respect to the paramagnetic case), was almost constant for non-magnetic impurities; as in experiments. In the case of 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