Nonlinear irreversible rf impedance of granular YBaCuO films

The properties of YBaCuO films are studied in the critical state at frequencies between 10 and 20 MHz in a parallel external magnetic field. The anomalous hysteresis phenomena and the effect of rf magnetic field and wave frequency on impedance components are investigated. The measured data are in qualitative agreement with those for metal ceramic plates. However, there is a significant quantitative difference between the effects of variable and static field amplitudes on impedance in plates and in films. The effect is about two-three orders of magnitude higher in films. The results are analyzed in terms of the critical state model for a thin-film geometry with a parallel varying field.

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