Critical currents and the effects of pinning

The bulk magnetic properties of sintered materials are treated as those of a standard magnetic material with a permeability dependent on the porosity. If J_c is expressed as a function of the internal H instead of the applied field, it is much more constant. The flux profile technique can then be used to extract J_c(B) at much lower fields than in bulk samples. A zero temperature flux creep mechanism is proposed but appears to be too small for the present computer simulation to detect. The effects of cobalt doping show that J _c is related to the depairing current. Increasing the coherence length decreases both inter- and intragrain critical currents, which are found to be affected in the same proportion. The causes of granularity and rapid flux creep are discussed, and it is concluded that there is no consistent explanation