Papers by Keyword: Superconducting

Abstract: We report the phase formation and electrical resistivity of MgB₂ superconductor samples. Method of synthesis was conventional solid-state reaction employing crystalline β-rhombohedral boron (B) and magnesium (Mg) with a stoichiometric ratio of Mg:B=1:2. The two precursors were mixed and sintered at various temperatures from 600°C to 900°C for an hour. All samples were characterized employing XRD, SEM, and Cryogenic Magnetometer. It is shown that the MgB₂ phase begins to form at a sintering temperature of 700°C. The highest peak intensity of the MgB₂ phase was observed in a sample sintered at 900°C indicates the largest fraction of the superconducting phase among all synthesized samples. Electrical resistivity values were carried out to investigate the superconducting properties of the samples. It is also shown the samples sintered at a temperature of 800°C and 900°C possess superconducting properties with a critical temperature of ~ 43 K

Abstract: We study the superconducting transition temperature T_c of F2/F1/S trilayers (Fi is a metallic ferromagnet, S is a s-superconductor), where the long-range triplet superconducting component is generated at canted magnetizations of the F layers. In this paper we show that it is possible to realize different spin-valve effect modes - the standard switching effect, the triplet spin-valve effect, reentrant T_c(α) dependence or reentrant T_c(α) dependence with the inverse switching effect - by variation of the F2/F1 interface transparency or the exchange splitting energy. In addition, we show that positionof the T_c minimum can be changed by joint variation of the F2/F1 interface transparency and the layerthicknesses.

Abstract: Fe_1.125Te alloys had been synthesized by solid state reaction methods. The effects of nitrogen annealing on Fe_1.125Te lattice structure and physical properties had been studied. It was found that the lattice constants a and c increased after annealed at temperature 400~600 oC. When the temperature is above 850 oC, the size of the unit cell returns to the similar size of original samples. The step-like magnetic-thermal curves were observed after annealed at 900 oC, which is associated with two magnetic transitions. In vacuum, the transition temperatures are 122 K and 128 K, while in the nitrogen, they are 122 K and 138 K. The resistance-temperature curves indicate a semiconductor to metal transition around 69 K for N₂ atmosphere.

Abstract: Measurements of internal strains in the superconducting constituent (Nb₃Sn phase in Nb₃Sn strand) in two cable-in-conduit conductors (CICC) for International Thermonuclear Experimental Reactor were performed using an engineering materials diffractometer TAKUMI of J-PARC. From strain measurements in a CICC for the toroidal field magnet after a performance test of cyclic current, in 100 mm long cut bars, a peak broadening and a large relaxation on residual strain were observed in Nb₃Sn phase at a portion received a high magnetic field (high field zone). Internal strain measurements were also conducted in a CICC for the central solenoidal magnets after the similar performance test, in the full-size shape as used in the performance test (3.6 m long) and in 100 mm long cut bars. Three main results were obtained. (1) Residual strain difference before and after the cutting to 100 mm long bar was about 0.1%, (2) a large relaxation on residual thermal strain was observed at the high field zone, and (3) the large relaxation on residual thermal strain at the high field zone was found mainly in a cross sectional side where the Lorentz force coming in.

Abstract: New materials play an important part in today high and new technology.Superconducting nanomaterial has become the most vibrant in new material research due to its unique physical and chemical properties. This paper focuses on how small-size effect affects superconducting transition temperature, and summarizes the concrete preparation methods of superconducting nanomaterials, hoping to provide a reference for material researchers.

Abstract: Nb based superconducting coplanar waveguide resonators on oxidized silicon wafer were fabricated and characterized at different temperatures. Crosstalk between two single resonators fabricated on the same chip was observed. When microwave signal is sent to the input of either resonator, output from both resonators show almost the same resonant frequency and similar quality factors.

Abstract: We investigate a two–dimensional single-band Hubbard model with a nearest–neighbor hopping. We treat a commensurate collinear order as well as incommensurate spiral magnetic phases at a finite temperature using a Hubbard–Stratonovich transformation with a two–field representation and solve this problem in a static approximation. We argue that temperature dramatically influence the collinear and spiral magnetic phases, phase separation in the vicinity of half–filling. The results imply a possible interpretation of unusual behavior of magnetic properties of single–layer cuprates.

Abstract: The effect of LCMO addition in YBCO system to investigate changes in structure and transport properties is reported. Samples with addition of (La_0.67Ca_0.33MnO₃)x (LCMO) (x=0.0-0.6) in YBa₂Cu₃O_7-δ (YBCO) superconducting system were prepared via solid state reaction. The effect of magneto resistive components on the superconducting properties of YBCO was investigated through X-Ray diffraction (XRD), resistance-temperature (R-T) measurement, and Scanning Electron Microscope (SEM). XRD analysis showed the addition of LCMO (0.2 wt% - 0.6 wt%) formed four new phases. The crystal system still orthorhombic with space group Pmmm after addition 0.2 wt% and 0.4 wt% of LCMO but the crystal system was changed to tetragonal and space group P4/mmm when addition with 0.6 wt% of LCMO. The temperature dependent of electrical resistance showed the samples were metallic above the transition temperature even though after addition. The T_c(onset) superconducting transition temperature decreased from 84 K to 66 K while the T_{c (offset)} decreased from 72°C to 54°C. This suppression was due to the magnetic behaviour of the LCMO. The average grain size decreased when addition with LCMO were increased.

Abstract: The deformation resistance of composite tapes was measured through compression tests. At room temperature, composite tapes were compressed and shaped at different deformation rates to different extents, and the real stress-strain curve of the composite superconducting tapes was obtained. Regression analysis was carried out on the curve using the Nonlinear Least Square Fitting (NLSF) method to acquire the parameters and coefficients regarding the curve, and a mathematical model for the deformation resistance of the composite superconducting tapes was built.