DIAMAGNETISM IN GRANULAR LA3BA3CACU7O16 WEAK-LINK EFFECTS

We show that for the La3Ba3CaCu7O16 ceramic, the effective grain size a, which plays a part in the ''granular'' phenomenon, is much smaller than the observed microstructural grain size. This fact induces strong differences between AC and DC susceptibilities due to the difficulty for the grains to adjust their phase in a static magnetic field becaus e a is smaller than lambda(J). The phase can be adjusted provided the amplitude of the alternative field remains low. As long as h(0) is low er than a given value, the AC field does not penetrate the grains and no difference is observed between ZFC and FC experiments. When h(0) in creases, the AC field goes into the grains and hysteresis occurs. The intergranular critical current density increases quickly with decreasi ng temperature; a crossover is observed between two regimes for the nu x-line movements on increasing the static magnetic field, an isolated and a collective behavior, respectively.