Flux patterns of monofilamentary Bi2Sr2Ca2Cu3O10+delta tapes at various temperatures

By means of magneto-optic imaging, flux patterns of monofilamentary, silver -sheathed Bi2Sr2Ca2Cu3O10+delta (Bi-2223) tapes are obtained at various tem peratures between 12 K and 77 K. Above 50 K, the flux distributions are fou nd to be nearly homogeneous, implying a uniform current flow. On decreasing the temperature, the observed flux patterns develop indications of granula rity. This effect is most pronounced at the lowest temperature investigated . From these observations we can deduce the temperature dependence of the t ransport current density, j(trans), and of the current density of the grain s, J(grain) We show that the appearance of granularity in the Aux patterns at low temperatures can be explained by assuming a very steep temperature d ependence of the intragranular current density, being large at low T and de creasing rapidly with increasing T until at about 50 K, j(grain) approximat e to j(trans) The absence of granularity above 50 K shows that the current flow is here dominated by the transport currents.