POSSIBLE ORIGIN OF THE ANOMALOUS MAGNETIZATION BEHAVIOR IN MELT-TEXTURED Y1BA2CU3O7-DELTA CRYSTALLITES

Magnetization measurements of the hysteresis loop, M(B), of melt-textu red Y1Ba2Cu3O7-delta (YBCO) crystallites were performed in external ma gnetic fields up to 10 T. The M(B) curves exhibit, between the superco nducting transition temperature T(c) and almost 39 K, a peak at a fini te field B which increases with decreasing temperature. The crystalli tes possess a high density of dislocations which could have been intro duced during the high temperature treatment and/or by stresses created due to differences in the lattice parameter of small inclusions and t he YBCO matrix. The large dislocation density together with the high s ensitivity of the superconducting order parameter on deviations from t he regular crystal structure and the small coherence length are sugges ted to be responsible for the observed fishtail shape of the magnetiza tion curves.