Severe vortex bending as large as 90°and giant avalanche were observed over a large area of a disk-shaped type-II superconductor in the mixed state using a contactless ultrasonic technique. This phenomenon is greatly different from a conventional critical state model in which the vortices are assumed to stand perpendicular to the disk plane. Equations describing the contactless ultrasonics are derived using a dynamic equation of vortex motion that takes account of crystal displacements arising

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... rom ultrasonic wave propagation. Using the equations and the ultrasonic data, the variations of the bending angle and the vortex densities are obtained as a function of applied magnetic field.