FLUX-PINNING EFFECT OF SMALL-SIZE DEFECTS IN YBA2CU3O7-DELTA

In this paper, it is reported that the small size defects, which result from the introductions of Y, Ba, Cu and O ionic vacancies and the partial substitutions of Ln (Gd, Sm, and Eu) for Y in YBa2CU3O7-delta system, may pin the flux lines. From the experimental results, authors suggest that the flux pinning effect at lower field relates to the magnetic interaction between the vortex and the surfaces of grains in the samples; and that the flux pinning at higher field belongs to the core interaction mechanism in the samples with ionic vacancies and stems from the elastic interaction between the vortex and the lattice stress field in the partially substituted samples.