Control of the critical current density in YBa2Cu3O7-delta films by means of intergrain and intragrain correlated defects

The aim of this work is to investigate the mechanisms controlling the curre nt-carrying capability of YBa2Cu3O7-delta thin films. A comparison between the magnetic properties of a film with intrinsic grain-boundary defects and two films crossed by columnar defects with different densities is presente d. Such properties have been studied by means of ac susceptibility measurem ents, resistivity measurements, and structural characterizations. The Clem and Sanchez model [Phys. Rev. B 50, 9355 (1994)] is used to extract critica l current values from the susceptibility data. In the virgin film, correlat ed grain-boundary defects were created among islands with homogeneous size, by means of the appropriate modifications in the growth process. Columnar defects were produced through 0.25-GeV Au-ion irradiation. The central issu e concerns the investigation of the plateaulike features characterizing the log-log field dependence of the critical current density, the analysis of the J(c) temperature dependence, and of the irreversibility line. An analyt ical expression of J(c) vs B is given in order to compare the main issues w ith the experimental data. This model suggests that the intergrain pinning dominates in the high-current/low-temperature regime through a network of f rustrated Josephson junctions, while the intragrain pinning is effective ne ar the irreversibility line; [S0163-1829(99)12433-0].