Flux pinning properties of nano-rods comprised of BaMO₃ (M = Zr, Sn) in REBa₂Cu₃O_7-δ thin films prepared by PLD method

We investigated the flux pinning properties of nano-rods comprised of BaZrO₃ and BaSnO₃ in REBa₂Cu₃O_7-δ (REBCO, RE: rare earth elements) thin films. The doping amounts of BaZrO₃ in YBa₂Cu₃O_7-δ thin films and BaSnO₃ in ErBa₂Cu₃O_7-δ thin films were varied with 0-3.5 wt% and 2.0-4.0 wt%, respectively. The in-field critical current density of 1.5 wt%-BaZrO₃-doped YBa₂Cu₃O_7-δ film was higher than those of any other samples measured in this study. The α values in the relation of J_c-B^-α are 0.2-0.3 for the BaZrO₃- and BaSnO₃-doped films. This fact shows the introduction of nano-rods is effective for the less magnetic field dependence of J_c. As one of the important results, it was found that the introduction of nano-rods caused the peak or kink in the magnetic field dependence of the pinning parameter m which was derived from the scaling of current-voltage characteristics. This phenomenon is the sign of the flux pinning due to the one-dimensional pinning centers. The peak fields of the BaSnO₃-doped films were slightly lower than those of the BaZrO₃-doped films, though the dope levels of the BaSnO₃-doped films were higher. This suggests that the diameter of BaSnO₃ nano-rods is larger than that of BaZrO₃ ones.