Does the diffusion mechanism in thin amorphous Co81Zr19 films change during structural relaxation?

In order to clarify the diffusion mechanisms in metallic glasses we measure d the time dependence and the isotope effect E = (D-alpha/D-beta - 1)/(root m(beta)/m(alpha)-1) of Co diffusion in thin 1 mum amorphous Co81Zr19 films during structural relaxation. To observe diffusion on a nanometre scale the radiotracer technique in conjunction with serial sectioning in conjunction with ion-beam sputtering was employed. A drop of the diffusivity by a fact or of three was found during structural relaxation at T = 573 K, but no cha nge in E was observed. Small isotope effects of E = 0.00(2) in the relaxed and even in the as-quenched states in the present alloy strongly suggest co llective hopping diffusion mechanisms in the relaxed as well as in the as-q uenched states. These results are in good accordance with results in thin 1 mum amorphous Co51Zr49 films. The results are compared to measurements in melt-spun amorphous Co76.7Fe2Nb14.3B7, where a drastic drop of E during rel axation has been observed. We further discuss the results with respect to m easurements in melt-spun Co89Zr11 ribbons to clarify the mechanism of annea ling defects. The absence of any geometry effect seems to rule out annihila tion of quenched-in free volume at the outer surface in thin Co-Zr glasses.