Scaling characteristics of AC magnetic susceptibility in the high-temperature superconductors with granular structure

The real and imaginary parts of the magnetic susceptibility of the Sn- an In-doped YBCO ceramic system were investigated. The magnetic behaviour of superconductors with granular structure is studied by the model of an assembly of superconducting loops due to Josephson junctions formed in the granular structure, which gives rise to some specific properties in their magnetic susceptibility. Experimental results in the AC magnetic susceptibility, including the onset of magnetic loss, the field and frequency dependence of the coupling temperature, the shape of the Φ″ vs. T curve, and the relation between Φ′ and Φ″, are able to be interpreted by our theory. Specific scaling of (T-T_b)/H ^{1 2} for the imaginary and real parts of the magnetic susceptibility is naturally introduced in our formalism, and it is well proved by the experimental data for both quantities. © 1995.