Impurity-doping effects on critical current properties in ErBa ₂Cu₃O_y films

We report on the critical current properties of the BaZrO₃(BZO)- and Co-doped ErBa₂Cu₃O_y thin films grown by the pulse laser deposition method. The BZO-doped Er123 films processed through the oxygen post-annealing showed clear enhancement of critical current density (J_c) in comparison with normal Er123 thin films. Even in the BZO doping level of 0.5 wt.% for Er123, TEM observation revealed that nano-rods of BZO were embedded in Er123 matrix, which was qualitatively consistent with a result of angular dependence of J_c at 77 K. The T_c values of the slightly Co-doped films depend on the substrate temperature, while irreversibility lines for the temperature normalized by T_c were almost coincident with one another, which were overlapped on that of the normal Er123 thin film. The positive Co-doping effect on J_c emerged at low temperatures. We believe that local regions with lower T_c, in which the Co doping levels in the CuO₂ planes were relatively higher than that of matrix, act as vortex pinning centers.