Magnetic field and temperature dependence of the transport critical current density and flux pinning in anisotropic (Bi,Pb) 2Sr 2Ca 2Cu 3O x high Tc superconductor

Abstract

Voltage-current characteristics ( V- I) in the temperature range 50–80 K and in magnetic fields up to 3 T have been measured on uniaxially pressed bulk (Bi,Pb) 2Sr 2Ca 2Cu 3O x (= 2223) samples in both parallel and perpendicular orientation of the external magnetic field B ext with respect to the direction of pressing. The critical current density J c determined from V- I, decreased in magnetic field exponentially with the characteristic field B s( T) in Bi-based 2212 samples. It was found that B s( T) in 2223 samples were significantly shifted towards higher temperatures. As for 2212 material, the reduced flux-pinning force density in 2223 samples scaled with B s; the shape of the scaling function was different in the two orientations of B ext. This result indicates that different mechanisms are responsible for flux pinning in various orientations of the external magnetic field. The shape of the voltage-current characteristics will be discussed.