Paramagnetic Meissner effect in mixed state of Y-Ba-Cu-O ceramics

In a narrow temperature range Delta T < 1 K in the vicinity of normal superconducting transition of Y-Ba-Cu-O ceramics the microwave impedance behavior correlates with the usual scheme of organization of superconductivity in a HTSC ceramics placed in external magnetic field. On further decreasing the temperature, instead of the expected decrease in the reactive component an abrupt increase is observed. The latter may be due to an additional positive contribution to the microwave magnetic susceptibility of a sample responsible for by the spontaneous orbital moments. The value of the positive contribution is inversely proportional to the intensity of the magnetic component of the microwave field in the resonator. When the sample goes to a paramagnetic state, temperature oscillating X(T)s appear below 90 K, which may be associated with the quantization of magnetic flux Phi(T) penetrating in the network of the Josephson junctions. It is supposed that the penetration of the magnetic microwave flux into the superconducting sample below 90 K takes place in the form of hypervortices.