Eur. Phys. J. B 7, 533-540 (1999)
https://doi.org/10.1007/s100510050646

Anomalous magnetic behavior of superconducting Tl₂Ba₂CaCu₂O₈ thin films in small magnetic fields close to the transition temperature

¹ Abteilung Festkörperphysik, Universität Ulm, 89069 Ulm, Germany
² National Laboratory for Superconductivity, Institute of Physics and Center for Condensed Matter Physics, P.O. Box 603, Beijing 100080, P.R. China

Received: 8 April 1998
Revised: 15 July 1998
Accepted: 2 September 1998
Published online: 15 February 1999

Abstract

Using a specially designed SQUID magnetometer we measured the temperature dependence of the critical current density in a ring patterned thin film for magnetic fields parallel to the c-axis. In addition, the temporal relaxation of the remanent state as prepared by field cooling in an external field of 100 Oe at different temperatures is determined. The data show a field-dependent anomalous kink close to T_c pointing to reduced dissipation with increasing temperature allowing to construct a corresponding H-T borderline. A similar behavior is observed for the normalized relaxation rate S(T) as extracted from the temporal behavior of the remanent state, which, at low temperatures, exhibits the expected increase for increasing T-values, while an anomalous decrease of S(T) is found for temperatures above 85 K. While the low-T regime is attributed to creep of 2D pinned single vortex lines, the high-T behavior is suggested to be dominated by collective motion with a more sluggish dynamics. This change in dynamics is also reflected by the activation barriers for flux creep U(j), which show a corresponding crossover in μ from 0.06 to 0.99. An additional scaling analysis of the E-j characteristics for according to vortex glass theory reveals quasi-2D collective creep behavior with .