The effects of columnar defects on the critical current density (Jc) and electric (E)vs. current density (J) characteristics were investigated for a YBa2Cu3Oy thin film prepared using a pulsed-laser deposition method. The YBa2Cu3Oy thin film was irradiated with 200 MeV Au ions from a direction θ=8.8°off the c-axis. Two peaks in the angular dependence of Jc were observed at the angles of θ=8.8°and θ=90°. These angles correspond to the directions of the columnar defect and intrinsic pinning, respectively. The E-J characteristics at various magnetic field angles can be described by the percolation transition model. The value of pinning parameter m increases at the angles of θ=8.8°and θ=90°. This result indicates that the efficiency of flux pinning is enhanced because fluxoids are effectively pinned by the columnar defects and intrinsic pinning or stacking faults in these directions.
To enhance the critical current density (Jc) in magnetic fields, we performed heavy-ion irradiation to introduce artificial pinning centers into YBCO—coated conductors. It is well known that high-energy heavy-ion irradiation introduces amorphous tracks along ion trajectories. Since the morphology and the size of the defect depend on the electron stopping power, Se, we used three different irradiation conditions, namely, 400 MeV Kr-ions, 450 MeV Xe-ions, and 500 MeV Au-ions, to study its effect. All of them enhance the in-field Jc, though the largest enhancement was observed after irradiation with 450 MeV Xe-ions. We also studied the dependence of Jc enhancement to optimize irradiation fluence. In all cases, the reduction of Jc was observed when the irradiation fluence exceeded 1 x 1012 ions/cm2, which may be attributed to the reduction of superconducting volume as well as the depression of superconductivity. From the angular dependence of Jc measurement, the columnar defects act as unidirectional pinning sites, as expected, but with a very large trapping angle of approximately 45°.