Microwave losses of YBCO thin films in high magnetic fields

A parallel plate resonator technique was employed to investigate changes in the microwave surface impedance between 20 K and 60 K, when d.c. magnetic fields up to 4 T were applied parallel to the YBCO film surface. By using a simple model to describe the observed behaviour, we can extract values for the vortex viscosity /spl eta/ and pinning constant /spl kappa//sub p/, as a function of temperature in three sets of films. As a result of low energy deuterium ion implantation in one of the films, the low field behaviour was degraded but at high fields the pinning properties improved quite drastically. A much smaller effect was observed in field dependence of the dc screening current as measured using vibrating sample magnetometry.<
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