Temperature dependence of critical currents in superconducting Bi-2212/Ag wires

Abstract

The temperature dependence of the critical current density has been studied in magnetic fields up to 12 T for Bi-2212/Ag round wires. In short specimens critical current densities of more than 10000 A/cm 2 have been achieved at 20 K and B = 8 T. In the case of sufficiently large values of the applied magnetic field, the critical current density j c is well described by the scaling law j c( B, T) = j sc( T)exp(− B/ B sc( T)) previously reported for melt processed Bi-2212 bulk material [1]. This scaling behaviour may be plausibly related to thermal activated flux creep. The shape of the resistive transition reflects flux creep effects as well as the homogeneity of the filaments, which is the dominant factor at low temperatures. Below 20 K a very small difference of the j c-values for increasing and decreasing applied fields has been observed. This hysteresis effect suggests that some weak links are present in the material. Finally, possible scaling laws for the volume pinning force will be discussed.