Evidence of highly collective Co diffusion in the whole stability range ofCo-Zr glasses

Using a radiotracer technique, we have measured the isotope effect E = d ln (D)/d ln(m(1/2)) of Co diffusion in CoxZr1-x glasses for 0.31 less than or equal to x less than or equal to 0.86. E is close to zero (E = 0 +/- 0.1) i n the whole range, covering 3 orders of magnitude in the diffusivity, despi te the existence of large activation volumes. These results strongly sugges t 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.