Institute of Physics of the National Academy of Scienses of Ukraine, 46 Nauki Ave., Kiev, 03028, Ukraine
Received February 28, 2006
For thin epitaxial films YBa2Cu3O7-d the temperature dependence of dynamic relaxation rate from 77 K to critical temperature Tc with and without magnetic field, and the dependence on magnetic field to 45 mT at 77 K have been investigated. It is shown that the experimental results are in good agreement with the previously proposed model of vortex lattice pinning, which suggests penetrative dislocations at
low-angle grain boundaries to be the main pinning centers in thin films. It follows from the experimental results that the effect of thermal fluctuations on the vortex pinning on penetrative dislocations and flux creep near Tc is not so crucial, as for pinning on linear defects in thick films and monocrystals. This conclusion is supported by the estimations, taking into account that the Abrikosov vortices in the thin film transform to Pearl vortices as the film temperature
approaches the critical point when the magnetic field penetration depth becomes greater than the film thickness. In this connection the mechanisms of flux pinning and flux creep in thin films are essentially collective even at very low magnetic fields and up to temperatures close
to Tc.PACS: 74.72.Bk - Y-based cuprates 74.78.Bz - High-Tc films 74.25.Qt - Vortex lattices, flux pinning, flux creep
Key words: YBCO, flux creep, thin films, Pearl vortex.