INITIAL CONDITIONS IN MAGNETIZATION DECAY OF HIGH-TC SUPERCONDUCTING THIN-FILMS

Magnetization decay measurements have been made on in situ grown YBa2Cu3O7-delta films at a variety of temperatures, applied magnetic fields, and initial applied magnetic field ramp rates. We find that the magnetization decay can be described based on the assumption of thermally activated flux vortex motion, both during the ramp in the applied field to establish the initial condition for the decay, and during flux creep. This implies that no cross-over from flux flow to flux creep occurs at short times during typical magnetization decay measurements. A short-time cross-over from linear to logarithmic decay, occuring at typically 0.1 sec, is deduced based on the assumption of thermally activated vortex motion.