Abstract
Measurements have been made of ultrasonic shear wave attenuation and sound velocity in highly textured polycrystalline samples of Bi 2 Sr 2 CaCu 2 O 8+y in magnetic fields up to 9 telsa and at temperatures down to 4.2 K. Magnetic field dependent attenuation peaks and velocity enhancements were found that are in good agreement with theoretical predictions based on the assumptions of the thermally assisted flux flow model of the mixed state. A pinning activation energy of ∼l60 K was deduced from the ultrasonic data. Pinning energy showed little evidence of dependence upon magnetic field magnitude or orientation. The flux-line lattice was found to be pinned fully at lowest temperatures.
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