Effect of dc field on ac-loss peak in a commercial Bi:2223/Ag tape

Measurements of the ac susceptibility in a commercial Bi:2223/Ag tape for some different ac magnetic field amplitudes, H-ac, in the presence of bias magnetic field H-dc directed along H-ac are reported. It is found that the peak values of the imaginary component of ac susceptibility x"(max) versus H-ac trace a valley for the orientation where applied field H-a perpendicular to wide face of the tape total. We note that the observation of the valley depends on various parameters such as field dependence parameter n in the critical current density, in the simple power law expression j(c)- alpha(T)/B-n, choice of the bias field H-dc together with selected ac field amplitudes H-ac, and dimension and geometry of sample studied. Our calculations based on critical state model with j(c) - alpha(1 - T/T-cm)(p)/B-n using the fitting parameters of n - 0.25, p- 2.2, T-cm- 108 K gives quite good results to compare the experimental and calculated curves.