FREQUENCY, FIELD, AND TEMPERATURE-DEPENDENCE OF THE AC PENETRATION DEPTH OF A GDBA2CU3O7-DELTA FILM IN THE MIXED-STATE

We report on asystematic mutual induction measurement of the complex A C penetration depth lambda of a sputtered high-quality GdBa2Cu3O7-delt a film in the mixed state by a very small coil system arranged near th e sample surface. The complex penetration depth lambda(B, T, omega) fo r DC inductions B less than or equal to 0.65 T (perpendicular to the f ilm), for temperatures 36 K less than or equal to T less than or equal to 81 K, and for frequencies 1 kHz less than or equal to omega/2 pi l ess than or equal to 500 kHz was determined from the measured signal b y a novel inversion scheme. The results are consistent with theoretica l predictions based upon single vortex pinning. The Labusch parameter alpha, the flux creep relaxation time tau, as well as the effective ac tivation energy U are simultaneously determined.