BISCCO Thin Films: Superconducting Phases, Irreversibility Line and Critical Current

Abstract

The transport properties such as irreversibility line (IL), critical current density (Jc), and activation energy (Ea) were studied in highly oriented BISCCO thin films with different superconducting phase relations H-2223:L-2212 by ZFC-FC method in the low magnetic field region (less than 0.1 T). The c-axis oriented BISCCO thin films with different superconducting phases H-2223:L-2212, high Tc phase (110 K), and low Tc phase (80 K), respectively, as determined by x-ray diffraction (XRD), were produced by r.f. magnetron sputtering on MgO (100) substrates and different post-annealing duration times. Tirr(H) data appear to be dominated by the intergrain Josephson flux. They exhibit the behavior of the grain coupling systems (similar to that displayed by spin glasses) and can be well described by a power law behavior like Almeida-Thoules. The irreversibility line (IL), however, was shifted to lower temperatures by decreasing the phase relation. The IL shifting to lower temperatures increases the liquid vortex region and would decrease the critical current density. The critical current density (Jc) and the activation energy (Ea) were determined using the 10 μVolt criterion and from Arrhenius plots of resistance data, respectively. Both decreased by decreasing the phase relation, i.e., by increasing the low Tc phase, which can be related to an increase in the granularity of films. The film granularity has been assumed as any crystal lattice defect, which creates a local depression of the superconducting order parameter.