IMPURITY DIFFUSION AND ISOTOPE EFFECT OF COBALT IN ALPHA-IRON

Impurity diffusion and the isotope effect of cobalt in alpha-iron have been studied by a serial radio-frequency sputter-microsectioning method with radioactive tracers Co-57 and Co-60 in the temperature range 859 to 1173 K. Larger influence of the magnetic spin ordering on the diffusion of cobalt than that on the self-diffusion in alpha-iron has been observed. In the ferromagnetic alpha-iron the diffusion coefficient of cobalt is about one half of the self-diffusion coefficient. Above the Curie temperature, the Arrhenius plot for the diffusion coefficient of cobalt approaches the linear Arrhenius line for the self-diffusion with increase of temperature as if the latter is the asymptotic line of the former. The increase in the isotope effect coefficient due to the magnetic spin ordering for the diffusion of cobalt in alpha-iron has been found to be larger than that for the self-diffusion. This suggests that the increase in the migration energy of a cobalt atom due to the magnetic spin ordering in alpha-iron is larger than that in the case of the self-diffusion.