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

Abstract

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 J_c values as high as 2.3×10⁵ A/cm² at 4.2 K, H=8 T (H⊥ab) have been obtained. The high J_c 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 J_c (transport) and J_c (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.