Pinning activation energies and the effect of cold deformation on critical currents in Bi(Pb)2223

We have measured magnetic hysteresis loops on silver sheathed Bi(Pb)2223 tapes. In these specially prepared tapes the grains are completely decoupled, thus allowing a determination of the intra-grain properties of Bi(Pb)2223. Mechanical deformation at room temperature causes fracture of the grains, but raises the critical current density by a factor of two. The irreversibility line appears not to be affected by the deformation. Using the generalized inversion scheme of Schnack et al. (1993) we have determined the flux pinning energies U(j,T), as well as the true (non-decayed) critical current density. Best fits are obtained in the local 2D single flux pancake pinning limit, and U(j/j/sub c/=0.1,T=0) is about 70 meV in a magnetic field of 0.2T perpendicular to the tape.<
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