Critical currents of YBa2Cu3O7 - δ epitaxial films, obtained by co-evaporation of yttrium, copper and BaF2 in an ultrahigh vacuum system, were measured using resistometric and magnetic torque methods. Typical values of jc $ ̌2 × 1011 A m-2 at 4.2 K and 4 × 1010 A m-2 at 77 K were found. In spite of their good quality these films exhibited large magnetic relaxation even at 4.2 K. Using the results of Monte-Carlo simulations of thermally activated flux motion for the analysis of the relaxation data typical values of 25 ± 3 meV were found for the activation energy U of flux motion at 4.2 K. It is shown that the occurrence of highjc values and small activation energies is not inconsistent in high Tc superconductors because of their short coherence lengths.@en

In this paper we present magnetic flux relaxation mea critical current Jc measurements on epitaxial coevaporated films of YBa2Cu3O7-δ superconductor. We measured a critical current of 3.5 * 1011 A/m2 at 4.2 K and 1.3 * 1010 A/m2 at 77 K. Jc depends strongly on the magnetic field B for B applied perpendicularly to the surface. The magnetization relaxation M(t) is logarithmic in time. In contrast to single crystals and polycrystalline samples the normalized magnetization relaxation tends towards a constant value at low temperatures and is weakly field-dependent.@en

We have investigated magnetic flux relaxation at low temperatures in a 90 nm epitaxial coevaporated film on YBa2Cu3O7-δ superconductor. This film is characterized by a high critical current Jc of 3.5 × 1011 A m-2 at 4.2 K, and 1.3 × 1010 A m-2 at 77 K. Although Jc depends strongly on the applied magnetic field B the magnetic relaxation is only weakly dependent on B. Also the magnetic relaxation does not vanish at zero temperature, indicating that besides a thermally activated process there is another intrinsic process working.@en