Vortex Dynamics in Nanostructured TFA-Grown YBCO Films Studied by Ac Susceptibility

Different successful approaches have recently merged to create artificial pinning centers in YBCO, in the quest to reach coated conductors with higher current performances. We have investigated by ac susceptibility how the different defects affect vortex pinning at high magnetic fields and temperatures, close to the irreversibility line. We analysed the ac response of different sorts of nanostructured YBCO films grown by the chemical solution growth TFA-route: YBCO-BaZrO₃ and YBCO-Y₂O₃ nanocomposites, and YBCO films with additional defects introduced by substrate nanodecoration. The non-linear Bean dynamic regime was studied in order to determine the field dependence of the effective energy barrier for thermally activated flux motion, U_e(H). Results evidence that BaZrO₃ and Y₂O₃ nanocomposites present peculiar field dependences that may be ascribed to the larger strong-isotropic pinning contribution induced by the isotropic microstrain emerging from the nanoparticles in the YBCO matrix.