By using the radio-tracers, 57Co and 60Co, an investigation was made of the isotope effect for Co diffusion in melt-spun amorphous samples at temperatures of between 626 and 642K. Ion-beam sputtering was used for serial sectioning. Measurements were also made of face-centered cubic Co at 1049K. The resultant isotope effect:

E = (D/D - 1)/[(m/m)1/2 - 1] = 0.74

for polycrystalline Co was typical of diffusion via monovacancies in densely-packed structures. The extremely small value of E (0.1) for the amorphous material ruled out a defect-mediated single atomic jump mechanism, and was consistent with a diffusion mechanism which involved about 10 atomic masses.

P.W.Hüppe, F.Faupel: Physical Review B, 1992, 46[1], 120-5