LOW-FIELD MICROWAVE MAGNETOABSORPTION IN GRANULAR HTSC MATERIALS

Previous measurements [Physica C 202 ( 1992) 151] of the universal 'vi rgin' curve of low-field microwave magnetoabsorption, in granular samp les of cuprate superconductors, have been expanded to cover a systemat ic study of the frequency and temperature dependence of the relevant p arameters. It is shown that the present results favor the weak-link (o r resistively shunted Josephson junction) model in preference to attri buting the magnetoabsorption to fluxon motion. A comprehensive study o f the hysteretic phenomena is also presented and it is shown that the hysteresis changes character when the field span exceeds a temperature -dependent 'threshold' value. An attempt is made to relate these effec ts to the existence of 'local' fields seen by the weak links.