Second step in the field-cooled magnetization of Bi-2212 single crystals

In all Bi-based superconductors [Bi2Sr2CaCu2O8+δ (Bi-2212), (Pb,Bi)2Sr2Ca2Cu3O10+δ] the critical current density, jc, is found to increase steeply when decreasing the temperature below ∼25 K (see, e.g.). In the case of Bi-2223 tapes, the pinning-dominated intragranular current density is found to increase considerably, whereas the transport current density shows only a small increase. Furthermore, determinations of the irreversibility line (IL) showed that there are two different regimes, a high field one with the irreversibility field Hirr∝exp(-T/T0), and a low field regime. (orig.)