Using a radiotracer technique, we have measured the isotope effect $E=d\ln \left(D\right)/d\ln \left(m^{1/2}\right)$ of Co diffusion in ${\mathrm{Co}}_x{\mathrm{Zr}}_{1-x}$ glasses for $0.31\le x\le 0.86$. $E$ is close to zero $(E=0\mathrm{}\pm 0.1)$ in the whole range, covering 3 orders of magnitude in the diffusivity, despite the existence of large activation volumes. These results strongly suggest a highly collective diffusion mechanism to be a quite general phenomenon in metallic glasses and point to diffusion via delocalized thermal effects at certain compositions.

• Received 10 November 1999

DOI:https://doi.org/10.1103/PhysRevLett.84.1467