Double Layered Thin Film Fabrication of a/c-controlled YBCO and Manganites, and Tunable Microwave Filters

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Double layers of Ferromagnetic/Hi-Tc-Superconductors (HTS) can be used for tunable microwave filters at base stations of mobile phone system. Permeability of Ferro-layer is modified by magnetic field, leading to modification of microwave propagation on HTS-layer. It is necessary to obtain single-layers and double-layers which complete such functions. Further, it is important to elucidate microwave absorption (MA) in HTS under magnetic field (H), problems of deteriorations under the double layers depositions and elapsed-degradations of thin films in application periods. In this project, we studied [1] thin film growths of Ferro-LSMO and-LBMO single layers, [2] double layer depositions of LSMO/YBCO and LBMO/YBCO (YBCO: HTS-layer), and their degradations, [3] microwave absorptions in HTS-YBCO and Superlattices under magnetic field.YBCO thin films were deposited on Mg0 and LAO substrates by Ion Beam Sputtering (IBS) with oxygen plasma supply. We succeeded to grow them at ultra-low temperat … More ures and obtained extremely smooth films. We could control a/c-orientation growths completely and elucidated a mechanism of a/c-orientations <surface migration>. Fine crystalline LSMO and LBMO thin films could be grown at ultra-low temperatures. LSMO showed 2D step-terrace growth mode. LSMO over-layers could be grown on a-YBCO under-layers but a part of a-YBCO was changed into c-YBCO. High quality YBCO over-layers could be grown on LBMO under-layers. During the double-layer depositions, the crystallinity of under-LBMO was not degraded but the double-layer surface was much roughened. The surface was very smooth when LBMO was deposited on YBCO layers but under-YBCO was degraded during the double-layer depositions. The crystallinity showed large elapsed-degradations for a few years for a-YBCO/Mg0 but not for a-YBCO/LAO. It was known that the degradation is concerned with lattice matching.High Tc (86 K) a-YBCO and c-YBCO were fabricated by PLD, and their MA was investigated under H. MA was larger for c-YBCO than for a-YBCO. MA was smaller for H//a than for H//c then it was clarified that a-YBCO is more useful for the double-layered tunable microwave filters. It was elucidated by theoretical analysis that an <excess screening current mechanism> is a major factor for MA. We measured MA on LCMO/YBCO superlattice, and found a quite important fact that MA is large for H perpendicular to the plane but negligible small for H parallel to the plane. Thus we could propose that we can minimize the microwave absorption in HTS-layers for the parallel magnetic field when the Ferro/HTS double-layers (superlattices) will be used for tunable microwave filters in the near future. Less