A. Heesemann et al., Does the diffusion mechanism in thin amorphous Co81Zr19 films change during structural relaxation?, NEW J PHYS, 3, 2001, pp. 61-67
In order to clarify the diffusion mechanisms in metallic glasses we measure
d the time dependence and the isotope effect E = (D-alpha/D-beta - 1)/(root
m(beta)/m(alpha)-1) of Co diffusion in thin 1 mum amorphous Co81Zr19 films
during structural relaxation. To observe diffusion on a nanometre scale the
radiotracer technique in conjunction with serial sectioning in conjunction
with ion-beam sputtering was employed. A drop of the diffusivity by a fact
or of three was found during structural relaxation at T = 573 K, but no cha
nge in E was observed. Small isotope effects of E = 0.00(2) in the relaxed
and even in the as-quenched states in the present alloy strongly suggest co
llective hopping diffusion mechanisms in the relaxed as well as in the as-q
uenched states. These results are in good accordance with results in thin 1
mum amorphous Co51Zr49 films. The results are compared to measurements in
melt-spun amorphous Co76.7Fe2Nb14.3B7, where a drastic drop of E during rel
axation has been observed. We further discuss the results with respect to m
easurements in melt-spun Co89Zr11 ribbons to clarify the mechanism of annea
ling defects. The absence of any geometry effect seems to rule out annihila
tion of quenched-in free volume at the outer surface in thin Co-Zr glasses.