The isotope effect for Co diffusion was measured in amorphous samples during structural relaxation. Radiotracer techniques and serial sectioning, using ion-beam sputtering, were used to study diffusion at the nm-scale. A sharp drop in diffusivity during structural relaxation of the thin films was found, and was of the same order of magnitude as that observed in much thicker glass samples. This was assumed to rule out the annihilation of quenched-in free volume at the outer surface. Unlike the case of melt-spun amorphous Co76.7Nb14.3Fe2B7, where a change in isotope effect from 0.5 (as-quenched state) to 0.1 (relaxed state) had been measured, no change in isotope effect was observed in Co51Zr49 during structural relaxation. The low value of the isotope effect in the relaxed and as-quenched states of the present alloy strongly suggested the operation of collective diffusion mechanisms in the relaxed and as-quenched states.

Isotope Effect of Co Diffusion in Thin Amorphous Co51Zr49 Layers during Structural Relaxation. V.Zollmer, H.Ehmler, K.Ratzke, P.Troche, F.Faupel: Europhysics Letters, 2000, 51[1], 75-81