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

In this paper, it is reported that the small size defects, which resul t from the introductions of Y, Ba, Cu and O ionic vacancies and the pa rtial substitutions of Ln (Gd, Sm, and Eu) for Y in YBa2CU3O7-delta sy stem, may pin the flux lines. From the experimental results, authors s uggest that the flux pinning effect at lower field relates to the magn etic 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 f rom the elastic interaction between the vortex and the lattice stress field in the partially substituted samples.