NONLINEAR IRREVERSIBLE RADIOFREQUENCY IMP EDANCE OF GRANULAR YBACUO FILMS

The properties of YBaCuO films are investigated in a critical state at frequencies 10-20 MHz in parallel external electromagnetic field. The effect of the strength of the static and rf fields and wave frequency on the impedance components as well as anormal hysteresis phenomena a re studied. The data obtained agree qualitatively with those for metal ceramic plates. Considerable quantitative disagreement is observed be tween the effective impacts of the alternative and static field amplit ude on the impedance of plates and films. In the films this relation i s two-three orders of magnitude higher. The results are explained in t he terms of the model of critical state for thin-film geometry with pa rallel variable field.