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 (Er123)/SrTiO3 thin films. Although critical temperatures (Tc) for the Co 0.5%-doped Er123 films decreased with substrate temperature (Ts), magnetic-field angular (θ) dependence of Jc for the films grown at lower Ts 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 Ts for the Co 0.1%-doped Er123 films. Remarkable c-axis peaks were not observed in Jc-θ curves and, however, Jc(H-parallel ab)/Jc(H-parallel 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 ∼90 K