Pinning analyses on epitaxial YBa2Cu3O7-δ films with BaZrO3 inclusions

The introduction of artificial pinning sites in YBa2Cu3O7-delta (YBCO) epitaxial thin films has been obtained by pulsed laser deposition (PLD) technique from YBCO-BaZrO3 (BZO) composite targets with BZO concentration ranging from 2.5 to 7 mol %. The typical critical temperature, T-c, drop observed in YBCO-secondary phase films grown by PLD has been successfully recovered by increasing the deposition temperature. Transport properties analyses revealed improved pinning force values for YBCO-BZO films for BZO concentration above 5 mol %. These films exhibited an anomalous dual peak structure which has been ascribed to the presence of two pinning contributions. The crossover field, B-m, separating these two pinning regimes has been observed to be temperature independent suggesting the occurrence of the matching field effect. The measured value of B-m agreed with the matching field value, B-Phi=Kn(d)Phi(0), as evaluated from transmission electron microscopy investigations. The mark of this phenomenon is retained down to 10 K, making YBCO-BZO more performing than pristine YBCO films at applied magnetic fields below B-m in all the temperature range inspected. On the contrary, in the high magnetic field range (above B-m), the effectiveness of correlated pinning is progressively reduced on lowering the temperature suggesting that at low temperatures the dominant pinning contribution arises from isotropic pinning centers. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3477451]