Ultrasonic studies of thermally assisted flux flow and intrinsic pinning in high- Tc phase Bi-Pb-Sr-Ca-Cu-O ceramics

Abstract

The temperature dependence of the ultrasonic attenuation coefficient α ( T, H) and sound velocity V s( T, H) were measured under magnetic fields for high- T c phase Bi-Pb-Sr-Ca-Cu-O ceramic samples aligned with the c-axis. In the case H · k , where k is the direction of sound propagation, a broad peak was observed in the α( T, 10T)-α( T, 0 T) versus T curve at T ∼ 65 K accompanied with a broad step in the V s( T, 10 T) - V s( T, 0 T) versus T curve. On the other hand, the peak and the step were also observed in the case of H | k , were the temperature position shifted down to T∼50 K, and the width was narrower than in H · k . The behavior was explained in terms of thermally assisted flux flow in which flux lines are pinned by intrinsic pinning centers.