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/D β − 1)/( m β /mα − 1) of Co diffusion have been measured in amorphous Co51Zr49 during structural relaxation. The radiotracer technique in conjunction with serial sectioning using ion-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 out annihilation of quenched-in free volume at the outer surface. In contrast to measurements in melt-spun amorphous Co76.7Fe2Nb14.3B7, where a change in E from E ≈ 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 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 state in the present alloy strongly suggests collective diffusion mechanisms in the relaxed and also as-quenched state.

Nanoscale diffusion in amorphousFe75Zr25films

“…43 These studies again support a collective mechanism for atomic diffusion in amorphous alloys. The present results, while in agreement with these earlier findings, 40,41,43 provide a deeper insight into the mechanism of diffusion in the unrelaxed state: we find that although the mechanism of diffusion involves a collective jump of a group of atoms in both unrelaxed and relaxed amorphous states, the average number of atoms participating in a diffusive jump exhibits variation in different regimes. In the lower-temperature range, where the quenched-in excess free volume is still not annihilated out, the average number of atoms participating in a diffusive jump is only 6, as compared to 22 in the relaxed state.…”

Evidence of Highly Collective Co Diffusion in the Whole Stability Range of Co-Zr Glasses

“…The vanishing isotope effect in the as-quenched state will be discussed elsewhere in connection with other results on the time dependence of diffusivity and isotope effect during structural relaxation and on the effect of quenched in-excess volume on diffusion [42]. Here we note only that, different from earlier results [43] in a metalmetalloid glass, we have no indications of single-atom jumps in the as-quenched state.…”

Iron self-diffusion in amorphousFeZr∕Fe57Zrmultilayers measured by neutron reflectometry

“…The authors attributed this to the fact that the evaporation produced well relaxed samples. Furthermore, Faupel et al, 39,40 found a significant isotope effect in the diffusivity of Co in melt-spun amorphous Co 76.7 Fe 2 Nb 14.3 B 7 while in sputter deposited amorphous Co 51 Zr 49 no isotope effect was observed. This difference was again attributed to a difference in the structure of as prepared melt-spun and sputter deposited amorphous alloy.…”