STRATIFICATION OF CURRENTS IN HARD SUPERCONDUCTORS IN CROSSED AC AND DC MAGNETIC-FIELDS

The superposition of currents in YBCO melt textured samples placed int o crossed ac and de magnetic fields is predicted and observed. This su perposition is a direct consequence of the critical state model. Owing to this nonlinear process, the area of the de magnetization loop dimi nishes and eventually disappears completely with an increase of the ac field magnitude. This means that under the action of the external ac field static magnetic properties of the hard superconductors change an d tend to the well known properties of the soft ones.