ULTRASONIC STUDIES OF TEXTURED SUPERCONDUCTING BI2SR2CACU2O8-FIELDS(YIN MAGNETIC)

Measurements have been made of ultrasonic shear wave attenuation and s ound velocity in highly textured polycrystalline samples of Bi2Sr2CaCu 2O8+y in magnetic fields up to 9 telsa and at temperatures down to 4.2 K. Magnetic field dependent attenuation peaks and velocity enhancemen ts were found that are in good agreement with theoretical predictions based on the assumptions of the thermally assisted nux flow model of t he mixed state. A pinning activation energy of similar to 160 K was de duced from the ultrasonic data. Pinning energy showed little evidence of dependence upon magnetic field magnitude or orientation. The flux-l ine lattice was found to be pinned fully at lowest temperatures.