Yoko Kanke

Current-Voltage Characteristics of YBa2Cu3Oy/La0.7Ca0.3MnOz/YBa2Cu3Oy Trilayered-Type Junctions

YBa2Cu3Oy(superconductor)/La0.7Ca0.3MnOz(magnetic material)/YBa2Cu3Oy(superconductor) trilayered-type junctions were prepared on MgO(100) single-crystal substrates, and the current-voltage characteristics were examined. The top and bottom YBa2Cu3Oy layers were 200 nm thick, and the La0.7Ca0.3MnOz layer was 20, 30, 50 or 100 nm thick. A supercurrent was observed through all the La0.7Ca0.3MnOz layers, even the thickest one. Further investigation showed that a supercurrent could he observed through the 500-nm barrier layer.

Preparation of Y−Ba−Cu−O thin films by rf-magnetron sputtering

Thin films of Y-Ba-Cu-O compound are prepared by rf-magnetron sputtering technique. Superconductivity appears for those films annealed at 900-930°C. The best thin films exhibit superconducting onset at 86 K and complete zero resistance at 76 K. From the X-ray diffraction analysis, it is found that the films annealed at 920°C have a strong c-axis orientation perpendicular to the film surface. The observed X-ray intensities are in good qualitative agreement with the calculated ones. The results of SEM and Auger electron spectroscopy are also presented.

Novel proximity effect between high-Tc superconductor and magnetic manganese oxide

Abstract A novel proximity effect between high-Tc superconductor and magnetic manganese oxide has been found. Supercurrents were observed through La0.7Ca0.3MnOz (LCMO) magnetic barrier as thick as 500 nm in YBCO/LCMO/YBCO trilayered junctions. We confirmed this proximity effect in coplanar-type junctions with spacing of 200 nm, and presented a possibility that this phenomenon occurs between NbN and LCMO. Furthermore we investigated current-voltage (I–V) characteristics and magnetic properties for Y1Ba2Cu3Oy/La1−xSrxMnOz(200nm)/Y1Ba2Cu3Oy (YBCO/LSMO/YBCO) junctions. I–V characteristics changed systematically with varying the magnetism of the barrier. When x value was 0.2, super-currents passed through the barrier, and it was found that ferromagnetism (Ms= 135 emu/cc) and supercurrents coexist in this proximity state. Magnetism of the LSMO is understood as a complicated and fluctuated state of ferromagnetic coupling in ab plane and antiferromagnetic coupling along c-axis. Considering supercurrents passed through the La1−xSrx(Mn3+1−xMn4+x)Oz along c-axis, our results suggest a novel proximity effect mechanism, that is antiferromagnetic spin fluctuation and charge fluctuation can transport Cooper-pairs over a long range.

Fabrication of YBa2Cu3Oy-La0.7Ca0.3MnOz-YBa2Cu3Oy coplanar junctions and their anisotropic current-voltage characteristics

Two types of YBa2Cu3Oy‐La0.7Ca0.3MnOz‐YBa2Cu3Oy (YBCO‐LCMO‐YBCO) coplanar‐type junctions with a 0.2 μm gap were fabricated by electron‐beam lithography and Ar‐ion‐beam milling. One is a junction in which a current flows into the a‐b plane (ferromagnetic spin arrangement) of the LCMO and then passes through the channel along the c axis (antiferromagnetic arrangement), and the other is a junction in which the current only passes through the a‐b plane. In the former junction the current‐voltage characteristics show nonlinearity which suggests a superconductive linkage, while the latter has linear characteristics. This anisotropy of the proximity effect is attributed to anisotropy of the spin structure, because the LCMO film has a small anisotropy of the normal decay length in the a‐b plane and along the c axis.

Fabrication of Y-Ba-Cu-O Superconductor/La-Ca-Mn-O Oxide Magnetic Material Layered Films

To investigate the interaction between a superconductor and magnetic material, fabrication of oxide superconductor/oxide magnetic material layered films was examined. From the secondary ion mass spectroscopic analysis, it was found that YBa2Cu3Oy can be fabricated on antiferromagnetic La0.3Ca0.7MnO3, and there is little reaction at the interface of these two layers. However, Bi2Sr2CaCu2Oy could not be fabricated because of mutual diffusion at the interface of Bi2Sr2CaCu2Oy and La0.3Ca0.7MnO3.

Effect of Substrate Temperature on the Crystalline State of Ba2ErCu3O7-x Superconducting Thin Films by rf Magnetron Sputtering

The crystalline state of the Ba2ErCu3O7-x thin films deposited at various substrate temperatures by rf magnetron sputtering are investigated. The as-sputtered films deposited above 650°C have a layered-perovskite structure which exhibits superconductivity by an annealing process in an oxygen flow. The annealed films have a better crystalline state and better superconducting properies than the films annealed after the deposition at lower substrate temperatures. The spatial distribution of the film composition across the thickness is also studied by Rutherford backscattering spectrometry.

Preparation and properties of Bi(Pb)-Sr-Ca-Cu-O films above 100 K by RF magnetron sputtering

Abstract Fabrication of Bi(Pb)-Sr-Ca-Cu-O thin films above 100 K by RF magnetron sputtering using a target containing Pb is reported. The superconducting and material properties of films under various sputtering and annealing conditions are studied. Thin films deposited at 700°C and annealed at 886°C in air exhibit a zero-resistivity temperature of 104 K. Dependence of high- T c phase growth on substrate temperature and annealing temperature is also presented.