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Abstract: La0.67Ca0.33MnO3 (LCMO)/YBa2Cu3O y (YBCO)/Ni trilayers were fabricated with varying thickness of the mid-superconducting YBCO layer. Two different deposition systems were used to avoid oxidation of the magnetic metal Ni and contamination of the deposition systems. Transport properties show that the temperature dependence of resistance goes from a metallic-to-metal–insulator transition (manganite-like behavior) to a superconducting behavior (M–M–S) with increase of the thickness of the YBCO layer. The magnetoresistance (MR) ratio is very small in comparison with LCMO/YBCO bilayers at low temperature. Such phenomenon may depend on the charge transfer and the magnetic spin interaction between the bottom and cap magnetic layers. [Copyright &y& Elsevier]

Abstract: Gd-doped poly-crystallized YBa2Cu3−xGdxO7−δ compounds with x=0–0.15 were synthesized using the solid-state reaction technique. We found that Gd3+ ions prefer to replace Cu at Cu(2) sites (CuO2 planar) within x<0.05, which may due to the ion size effect, and Gd3+ ions then begin to partially occupy Cu(1) sites (CuO chain) with increasing the doping content, which gives vital influence on superconductivity and spin-gap properties. There is no clear role on spin gap opening temperature played by magnetic element doping. [Copyright &y& Elsevier]

We have synthesized the La doped YBa2−xLaxCu3Oy ceramic cuprates with x&les;0.30 by the solid state reaction technique under the quenching temperature from 350 to 650 °C. X-ray diffraction and scanning electron microscopy studies indicate that all the synthesized samples contain one single phase. La is replacing for Ba at Ba-site in YBa2Cu3Oy. The unit cell volume varies with La content and with the quenching temperature. The thermal expansion for the unit cell volume at different quenching temperature is discussed. For the full oxidation samples the zero resistance temperature, Tc0, is almost unchanged with x&les;0.20 whilst Tc0 decreases with the increase of La content for the quenched samples. The spin gap opening temperature, Ts, for all the quenched and annealing samples are determined from the temperature dependence of resistance. [Copyright &y& Elsevier]

Polycrystallized Y1−xCaxBa1.9Nd0.1Cu3Oy (YCBNCO) compounds with x&les;0.40 were synthesized using standard solid state reaction technique. The structure for all samples was characterized by X-ray diffraction with Rietveld refinements. The transport properties for YCBNCO were measured by the standard four-probe method in the temperature range from 20 to 300 K. With the increase of Ca content, the variation of the superconducting transition temperature Tc can be divided into three regions: in the doping region I with x&les;0.10, Tc decreases sharply and linearly with x, which may relate to the competition between Ca2+ and Nd3+; in the region II with 0.10, Tc deviates the fitting line; and in region III with x&ges;0.25, Tc decreases slowly with increasing Ca content,which may relate to the formation of the Ca-rich phase. The dependence of resistivity on temperature, and the relation of the structural parameters versus the content of Ca were discussed. The Ca content dependence of the spin-gap opening temperatures in the normal state for YCBNCO was investigated. [Copyright &y& Elsevier]

The La2/3Ca1/3MnO3 (LCMO, tm=300 A˚)/YBa2Cu3O7−δ (YBCO, ts=20–500 A˚) heterostructural bilayers are prepared by the rf magnetic sputtering technique on SrTiO3 (STO) substrate at high temperature. Using the four-probe method, the electronic and magnetic transport properties have been investigated with and without magnetic field applied up to 4 T, The superconducting zero resistance temperature increases with the increase of the thickness of YBCO, ts, with ts>85 A˚. The nature of resistance for LCMO is screened by YBCO with the thickness more than about 250 A˚, but the magnetoresistance (MR) effect is observed in the bilayers. MR increases with the decrease of the thickness of YBCO. Structural characterizations of the bilayers show that there is interdiffusion appeared in the interface between LCMO and YBCO, and, LCMO and STO. [Copyright &y& Elsevier]