Thickness dependence of structural and superconducting properties of Co-doped BaFe₂As₂ coated conductors

High-quality Co-doped BaFe₂As₂ thin films with thickness up to 2 μm were realized on flexible metal tapes with LaMnO₃ as buffer layers fabricated by an ion beam-assisted deposition technique. Structural analysis indicates that increasing thickness does not compromise the film crystallinity, except for a small amount of impurities. Two types of thickness dependence of critical current density (J _c) were found: one is almost thickness independent in the range of 0.6-1.5 μm and the other is highly thickness dependent. In addition, the maximum value for crucial current I _c at 9 T and 4.2 K is about 55 A/12 mm-W for the 1.5-μm-thick film. Anisotropic Ginzburg-Landau scaling demonstrates that dominant pinning centers develop from correlated to uncorrelated with increasing film thickness. The further theoretical analysis shows that with film thickness increasing the pinning mechanism evolves progressively from a δl pinning to the δT pinning mechanism.