Dissipation in BSCCO/Ag 2212 ribbons

The low field DC irreversible magnetisation of BSCCO/Ag 2212 ribbons is shown to scale with the ribbon size. This indicates that the screening currents flow coherently throughout the sample, unhampered by the grain boundaries. At higher fields the samples ´fragment´ into macroscopic islands. Within these islands no weak link behaviour is evident and dissipation is dominated by intragranular flux motion. This is demonstrated by comparing the ribbon´s magnetisation loops with loops taken from the 2212 powder after it has been extracted from the ribbon. Transport measurements in magnetic fields at different angles with respect to the sample surface show how the j/sub c/(B) anisotropy is determined by the ´effective´ orientational distribution of the well-connected grains, underpinning the observation of intragranular flux motion being the dominant dissipation process at higher fields.<>