Frequency, field, and temperature dependence of the AC penetration depth of a GdBa2Cu3O7−δ film in the mixed state

Abstract We report on a systematic mutual induction measurement of the complex AC penetration depth λ of a sputtered high-quality GdBa 2 Cu 3 O 7−δ film in the mixed state by a very small coil system arranged near the sample surface. The complex penetration depth λ ( B , T , ω ) for DC inductions B ⩽ 0.65 T (perpendicular to the film), for temperatures 36 K ⩽ T ⩽ 81 K, and for frequencies 1 kHz ⩽ ω /2 π ⩽ 500 kHz was determined from the measured signal by a novel inversion scheme. The results are consistent with theoretical predictions based upon single vortex pinning. The Labusch parameter α, the flux creep relaxation time τ, as well as the effective activation energy U are simulateneously determined.