INFLUENCE OF PROCESSING ON THE LOW-FIELD MAGNETIC PHASE-DIAGRAM OF HIGH-TEMPERATURE SUPERCONDUCTORS

Low AC field magnetic phase diagrams in the (h(AC), T) plane have been deduced from AC susceptibility measurements for YBa2Cu3O7-delta sinte red polycrystals, magnetically melt-textured polycrystals and single c rystals. It is shown that dissipative regimes appear in all cases abov e a critical line located well below the irreversibility line, and the strongest shifts of the critical line against the irreversibility lin e are observed in magnetically melt-textured polycrystals. The relativ e positions of the irreversibility lines show that the increase of j(c ) in magnetically melt-textured polycrystals is relevant to the creati on of pinning sites with high activation energies.