Behavior of critical currents in Bi-Pb-Sr-Ca-Cu-O/Ag tapes from transport and magnetization measurements: Dependence upon temperature, magnetic field, and field orientation

Abstract

We have measured the dependence of the transport critical current density on magnetic field and temperature of a high-${\mathit{J}}_{\mathit{c}}$ Bi-Sr-Ca-Cu-O/Ag tape sample. At low temperature, ${\mathit{J}}_{\mathit{c}}$>${10}^4$ A/${\mathrm{cm}}^2$ extending to high fields as previously reported by several groups. For T>20 K and with the applied field parallel to the c axis ${\mathit{J}}_{\mathit{c}}$ declines precipitously with increasing field and temperature, reflecting the properties of intragranular pinning. The variation of ${\mathit{J}}_{\mathit{c}}$ with the angle between B and the tape normal is consistent with a two-dimensional model of the vortex lattice. Independent determination of ${\mathit{J}}_{\mathit{c}}$ by magnetic hysteresis measurement shows rough agreement with transport ${\mathit{J}}_{\mathit{c}}$’s at low fields but falls below by a factor that increases with increasing field and temperature. This can be accounted for by a model for thermally activated flux motion.