Field-dependence anomaly in critical currents and granularity for flux-grown single-crystal YBa2Cu3O7- delta

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Abstract
Magnetic hysteresis has been measured for a flux-grown YBa2Cu3O7- delta single crystal over the temperature range 4.2-80 K and in applied fields up to 12 T. Critical current densities jc have been derived from these data with the use of the Bean model. At temperatures between 20 and 70 K, it is found that the field dependence of the critical current has a peak in the medium field region. Successive division of the crystal gives a linear dependence of the magnetization M on the length scale R, which indicates that the current circulates around the whole sample. The shape of the magnetic hysteresis curve remains unchanged. Therefore the authors conclude that granularity is not the reason for the anomalous field dependence of the critical current density in their sample.