Critical current properties and microstructures in impurity-doped ErBa2Cu3Oy films

We report minute doping effects of cobalt on critical current properties and microstructures in ErBa2Cu3Oy (Er I 23)/SrTiO3 thin films. Although critical temperatures (T-c for the Co0.5%-doped Er123 films decreased with substrate temperature (T-s), magnetic-field angular (0) dependence of J(c), for the films grown at lower T, showed clear c-axis peaks. Also from a fact that defects along the c-axis direction were observed in their cross-sectional microstructures, the c-axis peaks were derived from existence of c-axis correlated vortex pinning centers. On the other hand, Tc is almost constant for the change in T, for the Co0.1%-doped Er123 films. Remarkable c-axis peaks were not observed in J(c)-theta curves and, however, J(c)(H vertical bar vertical bar ab)/Jc,(H vertical bar vertical bar c) was decreased compared with that of the pure Er123 films. Namely, minute doping of cobalt showed a reduction effect of electromagnetic anisotropy of the Er123 matrix within the Co-doping levels at which Tc was maintained in similar to 90 K. (C) 2007 Elsevier B.V. All rights reserved.