Comparison of flux pinning in superconducting Tl-Ca-Ba-Cu-O single crystals and thin films

The authors report direct observation of the flux pinning behavior of a Tl1Ca2Ba2Cu3Oy highly oriented thin film, a randomly oriented polycrystalline thin film and a Tl2CaBa2Cu2Oy single crystal. From the temperature dependence of the critical current densities Jc at zero field, activation energies U0 are estimated to be 110, 110 and 40 meV, respectively. Strong time-logarithmic magnetic relaxation M(t,T) was observed both in single crystals and in thin films. Within a thermally activated flux motion (TAFM) model, the distribution of activation energies ρ (U0) is determined from data on the time and temperature dependence of M(t,T) for the highly oriented film. The presence of a high-energy tail in the distribution suggests that the TAFM model can not be described by a single activation energy U0; the effective U0 value increases rapidly with temperature