Thermally activated depinning of individual vortices in YBa2Cu3O7 superconducting films

A number of YBa2Cu3O7 thin superconducting films have been grown on different single crystal substrates under different conditions using pulsed-laser deposition and magnetron sputtering techniques. Employing magnetization measurements, critical current density (J(c)) dependences on the applied magnetic field (B-a) have been obtained for the films. The analysis of the J(c)(B-a) behaviour suggests that the range of the B-a-independent J(c) plateau depends on the interplay between the vortex pinning of certain, particularly effective defects and thermally activated depinning of individual vortices. The latter process is found to be the main factor responsible for the temperature dependence of the size of the J(c)-plateau. This temperature behaviour is independent of the properties of the films and their orientation with respect to the field. The absolute J(c0) value at B-a --> 0 T is, in contrast to the plateau, more sensitive to pinning media transparency to the supercurrent flow. (C) 2004 Elsevier B.V. All rights reserved.