Analysis of the intergrain critical state of polycrystalline YBa2Cu3O7-δ using hollow cylinders

The magnetic field in the center of a superconducting YBa2Cu3O7-δ hollow cylinder is measured as a function of the applied field for temperatures ranging from 20 to 85 K. The aim of this paper is to explain the low-field hysteresis of the magnetization encountered in this and similar polycrystalline materials through the use of the generalized critical state model. Parameters of the model are determined by fitting the data giving an exponent close to n=2, a zero field critical current density Jc0 ranging from 0 to 1300 A/cm2, and a characteristic field H0 which varies from 0 to 125 G. A related study of the full penetration field as a function of the wall thickness is also presented. We include the effect of the demagnetizing factor in the theoretical analysis when the cylinders are short compared to their diameter and their wall thickness. This leads to a shielded volume fraction fg of the sample of around 0.55