Abstract
Magnetic-field-induced microwave absorption in sintered high-Tccopper oxide superconductors is found to be proportional to the surface area of samples and not to their volume, establishing that absorption takes place near the sample surface. The surface resistance and reactance increase with magnetic field as a result of energy loss through fluxons driven by superconducting currents. When the magnetic field is modulated, absorptive and dispersive signals arise from modulation of the complex surface impedance through processes induced by the changing magnetic fields. © 1988 IOP Publishing Ltd.