On the magnetization relaxation of ring-shaped Tl2Ba2CaCu2O8 thin films as determined by superconducting quantum interference device measurements

摘要

By using a superconducting quantum interference device (SQUID). the temporal relaxation of the magnetization was determined for ring-shaped Tl2Ba2CaCu2O8 thin films at various temperatures between 10 K and 80 K in magnetic fields ranging from 2 mT to 0.3 T. Based on these data, a detailed analysis has been performed related to the following methods or models: (1) Fitting the data to the thermally activated flux motion and collective pinning model; (2) Applying the Generalized Inversion Scheme to extract the temperature dependence of the unrelaxed critical current density j(c)(T) and pinning potential U-c(T); (3) Testing a modified Maley's method to obtain the current dependent activation energy for flux motion; (4) 2D vortex glass scaling. It is found that, for low fields (2 mT, 10 mT, 40 mT) the experimental data can be described by an elastic flux motion, most probably due to 3D single vortex creep. At higher fields (0.1 T, 0.2 T, 0.3 T), the observed behavior can be interpreted in terms of plastic flux motion which is probably governed by dislocation mediated flux creep. These high field data can also be consistently described by the 2D vortex glass scaling with scaling parameters nu(2D), T-0 and p being consistent with those derived from corresponding transport measurement. Also, results are presented demonstrating the importance of optimizing the scan length of the sample in a moving sample SQUID magnetometer to avoid artifacts. (C) 1998 Elsevier Science B.V. All rights reserved. [References: 37]