Observation of flux movement in quench-and-melt-grown YBCO generated by a pulsed magnetic field

The dynamics of the quantized flux in a ring-shaped YBa 2 Cu 3 O 7 sample has been studied through the observation of the magnetic flux motion generated by a pulsed magnetic field. The flux speed is obtained as a function of the rise rate of the external field and as a function of temperature. It is shown that the flux speed is not intrinsic as determined by the creep theory but is determined by the external field and the J c value. To interpret the slow rise of the observed signal, a distribution of different kinds of pinning centers in a sample is suggested.