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
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
Tc 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
.
PACS: 74.60.Ge – Flux pinning, flux creep, and flux-line lattice dynamics / 74.76.Bz – High-Tc films / 74.25.Dw – Superconductivity phase diagrams
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 1999