Dependence of surface resistance in HTS thin films on a DC magnetic field

We investigated the behavior of the surface resistance (R_s) of high-temperature superconductor (HTS) thin films exposed to a dc magnetic field (parallel to the c-axis). Measurements were done using the dielectric resonator method and superconducting magnet system. The DyBa₂Cu₃O_7-δ (DyBCO) and YBa₂Cu₃O_7-δ (YBCO) thin films (produced by THEVA GmbH) were prepared through a thermal co-evaporation method. The resonant frequency of the TE₀₁₁ mode in the resonator was approximately 22 GHz. A dc magnetic field of up to 5 T was applied vertically to two parallel superconducting thin films placed into a closed-type Cu cavity. R_s of the DyBCO and YBCO thin films increased as the applied dc magnetic field increased. The R_s ratio (defined as R_s(5 T)/R_s(0 T)) of the DyBCO and YBCO thin films at 4.5 K was approximately 5 and 50, respectively. These results indicate that the DyBCO thin film may be better for use in low-temperature nuclear magnetic resonance applications.