Investigation on the anisotropy of the current density characteristics andflux pinning in Ag-sheathed Bi-2223 tape

In the J-T curves of Ag-sheathed Bi-2223 tape, when the applied magnetic fi eld is perpendicular to the tape surface, the shape of the curves changes f rom the convex to concave. On the other hand, no such change is found in th e curves for B parallel to ab plane. Furthermore, a linear temperature depe ndence is observed in both applied held directions under zero field. In the J-B curves for different given temperatures, for B parallel toc axis, J de creases monotonously with increasing field, while for B parallel to ab plan e, a power-law relation of J proportional to Bn-1 at temperatures from 23 t o 60 K is observed with different exponent n in low field region, which cou ld be attributed to the presence of surface pinning. Mchenry and Sutton [Pr og. Mater. Sci. 38 (1994) 159] have suggested an empirical expression for t he effective pinning energy, which we have employed together with Anderson' s thermal activation theory of the flux bundle to estimate the value of the effective pinning energy. It is shown that the effective energy of the B p arallel to ab is about two times larger than that of B parallel toc axis du e to the strong intrinsic pinning of the tape. (C) 2001 Elsevier Science B. V. Ail rights reserved.