Isotope effect of Co diffusion in thin amorphous Co51Zr49 layers during structural relaxation

The time dependence and the isotope effect E = (D-alpha/D-beta - 1)/(root m (beta)/m(alpha) - 1) of Co diffusion have been measured in amorphous Co51Zr 49 during structural relaxation. The radiotracer technique in conjunction w ith serial sectioning using ion-beam sputtering was employed to observe dif fusion on a nanometer scale. A drastic drop of diffusivity during structura l relaxation in these thin films was found which is of the same order of ma gnitude observed in much thicker Co89Zr11 glasses (DORNER W. and MEHRER H., Phys. Rev. B, 44 (1991) 101). This seems to rule out annihilation of quenc hed-in free volume at the outer surface. In contrast to measurements in mel t-spun amorphous Co76.7Fe2Nb14.3B7, where a change in E from E approximate to 0.5 in the as-quenched state to E approximate to 0.1 in the relaxed stat e has been measured (RATZKE K. et. al., Phys. Rev. Lett., 68 (1992) 2347), no change in E has been observed in Co51Zr49 during structural relaxation. The low value of E = 0.01(2) in the relaxed and even in the as-quenched sta te in the present alloy strongly suggests collective diffusion mechanisms i n the relaxed and also as-quenched state.