Observation of a linear regime in imaginary chi(ac) of Bi-2223 superconductor

Measurements of complex AC susceptibility were performed on Bi-2223/Bi-2212 high T-c superconductor at low excitation field amplitudes. Unusual features attributable to the Bi-2223 phase are observed in the imaginary part of the AC susceptibility, chi ''(T), at different Excitation field amplitudes, H-m. The peak temperature, T-p as a function of H-m defines a region in (H, T) plane, where chi '' is independent of H-m. Various possible interpretations are discussed, including that of a transition to a viscous flux flow regime.