Isotope effect of Co diffusion in thin amorphous Co ₅₁ Zr ₄₉ layers during structural relaxation

Abstract

The time dependence and the isotope effect E = (Dα/Dβ − 1)/(√mβ/mα − 1) of Co diffusion have been measured in amorphous Co51Zr49 duringstructural relaxation. The radiotracer technique in conjunction with serial sectioning usingion-beam sputtering was employed to observe diffusion on a nanometer scale. A drastic drop of diffusivity during structural relaxation in these thin films was found which is of the same order of magnitude observed in much thicker Co89Zr11 glasses (Dörner W. and Mehrer H., Phys. Rev. B, 44(1991) 101). This seems to rule outannihilation of quenched-in free volume at the outer surface. In contrast to measurements inmelt-spun amorphous Co76.7Fe2Nb14.3B7, where a change in E fromE ≈ 0.5 in the as-quenched state to E ≈ 0.1 in the relaxed state has been measured (Rätzke K. et. al., Phys. Rev. Lett., 68 (1992) 2347), no change in Ehas been observed in Co51Zr49 during structural relaxation. The low value of E = 0.01(2) in therelaxed and even in the as-quenched state in the present alloy strongly suggests collective diffusion mechanisms in the relaxed and also as-quenched state.