Evidence for the lattice-mismatch-stress-field induced flux pinning in (Gd 1 − xY x)BA 2Cu 3O 7 − σ thin films

Abstract

By partially substituting Gd with Y in GdBa 2Cu 3O 7 − σ thin films, the measured critical current density ( j s) was increased, while the relaxation rate ( S) was clearly lowered, which was attributed to the presence of extra pinning centers. The temperature dependence of the true critical current density j c( T) and the pinning potential U c( T) were determined from the experimental data both for the pure and the substituted thin films by means of a generalized inversion scheme (GIS). It is found that the experimental results for the pure film are close to the predictions of the σl pinning model, while those for the substituted thin film follow the theoretical expressions derived for the single-vortex collectively pinned by the small size stress-field pinning centers, which may suggest that the enhanced pinning in the substituted sample is probably due to the presence of a local stress field induced by the lattice mismatch.