Impurity diffusion, and the isotope effect, for Co in -Fe were studied by using a serial radio-frequency sputter-microsectioning method and the radioactive tracers, 57Co and 60Co, at temperatures ranging from 859 to 1173K (table 51). A larger effect of magnetic spin ordering upon Co diffusion, than upon self-diffusion, in -Fe was observed. In ferromagnetic -Fe, the Co diffusion coefficient was equal to about 50% of the self-diffusion coefficient. Above the Curie temperature, the Arrhenius plot for Co diffusion approached the linear Arrhenius line, for self-diffusion, with increasing temperature; as if the latter was the asymptote of the former. The increase in the isotope effect coefficient, due to magnetic spin ordering, for Co diffusion in -Fe was found to be larger than that for self-diffusion. It was suggested that the increase in the migration energy of a Co atom, due to magnetic spin ordering, in -Fe was larger than that in the case of self-diffusion.

Y.Iijima, K.Kimura, C.G.Lee, K.Hirano: Materials Transactions, 1993, 34[1], 20-6

Table 51

Diffusivity of Co in -Fe