IRREVERSIBLE CHANGE OF SURFACE IMPEDANCE OF HIGH-T-C THIN-FILMS DUE TO DC MAGNETIC-FIELD COMMUTATION

The magnetic field dependence of the surface impedance (resistance and reactance) of high-T-c thin films is found employing measurements of the quality factor and the frequency of the parallel plate resonator i n a dc magnetic field up to 500 Oe at 10 GHz. c-Oriented YBa2Cu3O7 thi n films are examined. Enhancement of surface resistance and inductance with increase of magnetic field is observed. The effect of irreversib le increase of surface impedance as compared to its initial values aft er a cycle of magnetic field commutation is found. A qualitative expla nation of the observed effects based on the picture of magnetic vortex penetration and accumulation in the film due to strong pinning is pre sented.