Reduced intrinsic and strengthened columnar pinning of undoped and 4 wt% BaZrO3-doped GdBa2Cu3O7-δ thin films: a comparative resistivity study near Tc

The resistivities of undoped and 4 wt% BaZrO3-doped (BZO) GdBa2Cu3O7-δ (GdBCO) thin films were measured in a temperature activated flux-flow regime (TAFF). In addition, resistivity versus rotation angle of magnetic field, ρ(Θ), measurements were done near the critical temperature, Tc. The results of undoped and doped GdBCO were compared with ones of YBCO, and they showed that YBCO has better intrinsic pinning of CuO-planes than GdBCO. This is explained by the extra stacking faults distorting the ab-planes in GdBCO. The BZO-doping increased activation energy, U0, in B||c geometry at fields higher than 1 T in YBCO and 3 T in GdBCO, but reduced U0 in the Bperpendicularc direction in the whole measured magnetic field range. Also, the irreversibility field, Birr, was enhanced in BZO-doped GdBCO at fields higher than 3 T in B||c, but was reduced in the Bperpendicularc direction. The reduction of U0 and Birr in the Bperpendicularc direction in BZO-doped films is explained by BZO nanorods distorting the ab-planes, too. The distortion may explain the more isotropic ρ(Θ) in GdBCO and BZO-doped material. The 4 wt% BZO-doping seems to be more effective on GdBCO, and we suggest that either cation substitution, excess strain caused by the interaction of the extra stacking faults and BZO nanorods, or oxygen deficiency result in nanosized regions whose superconducting properties are reduced and which act as extra pinning sites. According to the resistivity measurements near Tc, the undoped YBCO should be used if high pinning of the ab-planes is needed. Further, from these materials 4 wt% BZO-doped GdBCO is best suited for applications where high magnetic fields are needed at high temperatures.