c-Axis-correlated pinning properties in heavy-ion-irradiated Y123 films

The introduction of the c-axis-correlated disorder is a promising technique for the improvement of the critical current density J_c for B ∥ c of the REBa₂Cu₃O_y films and tapes. In order to understand the vortex pinning state diagram of typical c-axis-correlated disorder, the angular dependence of J_c was measured in detail for Y123 films with columnar defects induced by heavy-ion irradiation. We found that the peak in the angular dependence of J_c at the parallel external field to the c-axis (B ∥ c) becomes sharp and large with increasing a magnetic field across the matching magnetic field at various temperatures. Hence, the c-axis-correlated pinning works well even in much higher magnetic fields than the matching magnetic field. Those behaviors suggest that the interstitial vortices, which locate in between vortices pinned by the c-axis-correlated disorders, are also trapped through the elastic interaction of the vortices.