MAGNETIC-PROPERTIES AND AC-LOSSES OF SUPERCONDUCTORS WITH POWER-LAW CURRENT-VOLTAGE CHARACTERISTICS

In many high-T(c) superconductors the critical current density j(c) is an ill-defined quantity due to the smooth current-voltage characteristic. Since j(c) is the basic parameter entering the critical state model, its application to such materials becomes problematic. In this paper, a theory of magnetic properties and AC-losses in superconductors with smooth current-voltage characteristics is proposed. It is applied to superconductors with a power law characteristic, E approximately j(alpha). The AC-losses are calculated analytically; simple scaling rules are obtained for their dependence on the frequency and the field amplitude. Moreover, it is shown that the normal ohmic conductor and the ''perfect'' type-II superconductor (critical state) emerge as limiting cases, alpha = 1 and alpha = infinity, from the theory.