Particle size dependence of zero-field microwave absorption in powdered Bi - Sr - Ca - Cu - O superconductors

The non-resonant magnetically modulated microwave response measurements of powdered Bi - Sr - Ca - Cu - O samples using the conventional EPR spectrometer are presented. After cooling in a near zero magnetic field, all samples exhibited a sharp (about ) microwave absorption with applied magnetic field, superimposed on the widely observed and well explained broader minimum. The width of the absorption maximum is found to be dependent on the particle size. It becomes broader with decreasing particle size. The effects of particle size and field history on the peak are given in detail and some possible mechanisms to account for the observations are presented.