Critical current density and granularity in crystals of K3C60 fulleride

The temperature dependence of the critical current density Jc(T) in superconducting fulleride K3C60 crystals is investigated on the basis of magnetization measurements in these materials. According to ac susceptibility data, the best crystals do not exhibit granularity for supercurrent flows, and can be regarded as single crystals from this point of view. The obtained results on Jc in K3C60 are compared with those for other crystalline and powder-type compounds AxByC60. Possible granularity of the crystals and its influence on Jc are discussed in detail. The irreversibility line for a K3C60 single crystal is also determined.