Flux Jumping in Synthetic High-Field Superconductors

The magnetic field, Hfj, of the first flux jump during the initial magnetization of synthetic high-field superconductors, composed of indium in porous glass, has been measured as a function of the temperature and the field-sweep rate dH/dt. The behavior is reasonably well described by Hfj∝log(dH/dt). At low values of dH/dt, log Hfj is approximately proportional to 1/(dH/dt). It is shown that under rather special conditions the flux-jumping behavior depends upon the condition of the sample surface.