Electromagnetic properties of brickwork-like structured hard superconductors

The low-frequency surface impedance of melt-textured hard superconductors is studied both theoretically and experimentally. The electrodynamic properties of these materials can be described by a simple model which takes into account their brickwork-like structure. This model represents a generalization of the critical-state for a situation where the main pinning of the vortex system is affected by intercrystalline boundaries. An experimental confirmation of our model is presented. The main result consists in a theoretical prediction of a quasibarrier preventing the penetration of an ac magnetic flux into a melt-textured superconductor. A contactless method to determine the nonuniform spatial distribution of the critical current density caused by nonuniform pinning is proposed.