Microwave properties of DyBa2Cu3O7−δ monodomains and related compounds in magnetic fields

We present a microwave characterization of a DyBa2Cu3O 7−x single domain, grown by the top-seeded melt-textured technique. We report the ͑a , b͒ plane field-induced surface resistance, ⌬Rs͑H͒, at 48.3 GHz, measured by means of a cylindrical metal cavity in the end-wall-replacement configuration. Changes in the cavity quality factor Q against the applied magnetic field yield ⌬Rs͑H͒ at fixed temperatures. The temperature range ͑70 K;Tc ͒ was explored. The magnetic field ␮0 H Ͻ 0.8 T was applied along the c axis. The field dependence of ⌬Rs ͑H͒ does not exhibit the steep, steplike increase at low fields typical of weak links. This result indicates the single-domain character of the sample under investigation. ⌬R s ͑H͒ exhibits a nearly square-root dependence on H, as expected for fluxon motion. From the analysis of the data in terms of motion of Abrikosov vortices, we estimate the temperature dependences of the London penetration depth ␭ and the vortex viscosity ␩, and their zero-temperature values ␭͑0͒ = 165 nm and ␩͑0͒ = 3 ϫ 10−7 N s m−2 , which are found in excellent agreement with reported data in YBa2Cu3O 7−x single crystals. Comparison of microwave properties with those of related samples indicates the need for reporting data as a function of T / T c in order to obtain universal laws. © 2008 American Institute of Physics.