The YBa2Cu3O7-δ anomalous second peak and irreversible magnetic field in the magnetization hysteresis cycles

The flux jumps, the second peak and the irreversible magnetic field in the magnetization hysteresis cycles have been investigated in the high temperature superconductor YBa2Cu3O7-δ single crystals. These cycles were obtained for different temperature values, the applied magnetic fields up to 6 T and the angle θ between the applied magnetic field and c-axis. The magnetization curves exhibit a remarkable second peak ''fishtail'', this second peak was not observed for the low temperature, but we observed the flux jumps ''saw tooth''. The temperature dependence of the irreversible magnetic field, Hirr, for the applied magnetic field perpendicular to the ab planes is given by an extended expression, Hirrα(1-T/T c) α, where α is a constant, the Abrikosov flux dynamics can explain this behavior. The H irr as a function of θ has been strongly influenced by the flux pinning and the thermally assisted flux motion. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)