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

Abstract

In the J– T curves of Ag-sheathed Bi-2223 tape, when the applied magnetic field is perpendicular to the tape surface, the shape of the curves changes from the convex to concave. On the other hand, no such change is found in the curves for B‖ ab plane. Furthermore, a linear temperature dependence is observed in both applied field directions under zero field. In the J– B curves for different given temperatures, for B‖ c axis, J decreases monotonously with increasing field, while for B‖ ab plane, a power-law relation of J∝ B n−1 at temperatures from 23 to 60 K is observed with different exponent n in low field region, which could be attributed to the presence of surface pinning. Mchenry and Sutton [Prog. Mater. Sci. 38 (1994) 159] have suggested an empirical expression for the 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‖ ab is about two times larger than that of B‖ c axis due to the strong intrinsic pinning of the tape.