Anomalous microwave absorption in GdBCO powder: π junctions and the paramagnetic Meissner effect

Abstract

We have observed anomalous microwave absorption (MWA) representative of paramagnetic Meissner effect in GdBCO powder. The results are discussed in terms of π junction theory. The phase change in the MWA gives evidence for the change in behaviour of the π junctions from para to dia state. The intragrain weak links with high Jc are likely to be forming π junctions in the sample. It is expressed that the high frequency absorption is a better tool than the magnetization measurements to investigate the π junctions. Thermally induced vortex-antivortex pair formation and the flux compression caused by an inhomogeneous superconducting transition are ruled out as the possible mechanisms of the PME, from the microwave absorption study. © 1998 Elsevier Science B.V.