NONUNIFORM MAGNETIC-FLUX DISTRIBUTION IN HIGH-TC CERAMICS AND HYSTERETIC BEHAVIOR OF CRITICAL CURRENT

Magnetic flux expulsion from superconducting granules results in a difference between the external magnetic field, H, and the field, H(o), in the intergranular regions of granular superconducting systems, such as high T(c) ceramics. The influence of flux expulsion on the field dependence of the critical current, j(c)(H), is discussed, taking into account the Bean - Livingston surf ace barrier and intragranular pinning. These effects determine the behaviour of j(c)(H) for systems with large closely packed granules in the field range up to several times H(c) (where H(c) is the thermodynamic critical field of the granules). In particular, strong hysteresis of the j(c)(H) curve may be observed.