CRITICAL CURRENTS AND THE EFFECTS OF PINNING

The bulk magnetic properties of sintered materials are treated as 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 our 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 intra grain critical currents, which are found to be affected in the same proportion. The causes of granularity and rapid flux creep are discussed. It is concluded that there is no consistent explanation.