Temperature dependence of the vortex remanent state in high-Tc superconductors

Temperature and magnetic field dependence of the vortex penetration into a superconductor and the resulting trapped vortex field (the vortex remanent state) were investigated for Bi2Sr2CaCu2O8+x (BSCCO) and YBa2Cu3O6+x (YBCO) single crystals and BSCCO thin films. The experiments revealed changes in the pinning regime (the magnitude and magnetic relaxation) of the trapped vortex field with an increasing temperature. The trapped vortex field, obtained by applying a constant magnetic field, exhibits a maximum at a certain temperature, that separates the partial vortex penetration regime at low temperatures from the complete vortex penetration state at higher temperatures. The corresponding vortex remanent states in these two regimes are characterized by two distinctly different relaxations, the logarithmic and the nonlogarithmic ones at temperatures below and above the maximum, respectively, for both BSCCO and YBCO. At temperatures close to T-c surface/geometric barrier affect the relaxation rates.