THE EFFECTIVE FLUX-PINNING ENERGY U(J) OF AG-BI-2223 TAPE BY AC SUSCEPTIBILITY MEASUREMENTS

A new method based on the nonlinear flux diffusion model was used to s tudy flux pinning and critical current density J(c) of Ag-Bi-2223 tape . Complex a.c. susceptibility was measured systematically as a functio n of temperature T, a.c. field amplitude h, frequency f and d.c. field H-d. The dependence of effective barriers U on T, H-d and current den sity J were determined to be U(J, H-d, T) = AJ(-mu)H(d)(-v)(1 -T-2/T-c (2))(2), where A = 8.0 x 10(4)(A cm(-2))T-mu(v) K, mu = 0.45 and v = 0 .75. The results are consistent with those determined by other experim ents. J(c) as a function of T and H-d, J(c)(T, H-d), is estimated and compared with those measured directly by the transport four-probe meth od. It is therefore shown that the a.c. susceptibility technique is al so a powerful tool for the study of Ag-Bi tape samples.