2-DIMENSIONAL VORTEX DYNAMICS IN YBA2CU3O7/PRBA2CU3O7 MULTILAYERS

The isochronal spectra of magnetic aftereffect in the amorphous alloys Fe90-xCoxZr10 were measured within a temperature range of 77-450 K and over a time interval of 1 to 180 s. The spectra are characterized by a temperature-independent relaxation process at lower temperatures (less than 190 K) and a well-defined relaxation peak around 350 K which, for the samples with x 30 are completely irreversible. The current results can be described by a two-level system constructed of mobile atom pairs, and a quantitative analysis performed on the typical Fe-rich sample leads to an activation enthalpy spectrum ranging from 0.6 to 1.6 eV and a small preexponential factor tau0 = 2.224 X 10(-16). In addition to the atom-pair mechanism, the rearrangement of the spin direction is also assumed to explain the concomitant relaxation peaks in the Fe-rich samples.