Critical currents and magnetization in c -axis textured Bi-Pb-Sr-Ca-Cu-O superconductors

Transport critical currents and magnetization behavior in c-axis textured Bi-Pb-Sr-Ca-Cu-O superconductor ribbons have been studied. The highly oriented layer structure was achieved by a combination processing of spray coating on silver foil, cold rolling, and partial melting. Transport Jc values as high as 2.3×105 A/cm2 at 4.2 K, H=8 T (H⊥ab) have been obtained. The high Jc at H≥5 T is maintained to temperatures near 20 K but it vanishes completely at or above ∼30 K, thus showing the limitation in useful, high-field operating temperatures for the Bi-system superconductors. A comparison of Jc (transport) and Jc (magnetization) indicates that the size scale of the circulating supercurrent loop in the Bean model nearly corresponds to the whole sample dimension rather than the orders-of-magnitude-smaller grain size. This demonstrates that the a-b grain boundaries in the melt-processed ribbons are not weakly coupled. The time decay of magnetization has also been studied.