The Angular Dependence of the Critical Current of BaCeO3 Doped YBa2Cu3O6+x Thin Films

The angular dependencies of the critical current of BaCeO3 (BCO) doped YBa2Cu3O6+x (YBCO) thin films grown with pulsed laser deposition (PLD) on SrTiO3 (001) were systematically investigated. The BCO concentration in the YBCO matrix was varied between 0-8 wt.%. Transmission electron microscopy confirmed that the 4% BCO containing sample has point-like, partly agglomerated BCO particles with diameter of 2.5 nm. The dopant degrades the crystal quality of YBCO but improves its in-field current carrying performance especially at low temperatures. The BCO addition affects the angular dependence of the critical current by broadening the B parallel to ab-axis peak of YCBO but no c-axis peak is seen, which is contrary to BaZrO3 doped films made by PLD. Although the particles are point-like, it is found that a model featuring only isotropic pinning centers is not sufficient to describe the angular dependence of the samples where B parallel to ab-axis of YCBO.</p

X-ray photoelectron spectroscopy of superconducting RuSr2Eu1.5Ce0.5Cu2O10RuSr_2Eu_{1.5}Ce_{0.5}Cu_2O_{10} and nonsuperconducting RuSr2EuCeCu2O10RuSr_2EuCeCu_2O_{10}

We report x-ray photoelectron spectroscopic investigation of $RuSr_2Eu_{1.5}Ce_{0.5}Cu_2O_{10}$ with ferromagnetic TC\sim100 K and a superconducting transition temperature of $\sim$30 K compared with $RuSr_2EuCeCu_2O_{10}$, which is a ferromagnetic (TC\sim 150 K) insulator. Our results show that the rare earths, Eu and Ce, are in 3+ and 4+ states, respectively. Comparing the Ru core level spectra from these compounds to those from two Ru reference oxides, we also show that Ru in these ruthenocuprates is always in 5+ state, suggesting that the doped holes in the superconducting compound arising from the substitution of $Ce^{4+}$ by $Eu^{3+}$ are primarily in the Cu-O plane, in close analogy to all other doped high-$T_C$ cuprates. Analysis of Cu 2p spectra in terms of a configuration interaction model provides a quantitative description of the gross electronic structures of these ruthenocuprates

X-ray photoelectron spectroscopy of superconducting RuSr2Eu1.5Ce0.5Cu2O10 and nonsuperconducting RuSr2EuCeCu2O10

We report x-ray photoelectron spectroscopic investigation of RuSr2Eu1.5Ce0.5Cu2O10 with ferromagnetic T-C similar to 100 K and a superconducting transition temperature of similar to 30 K compared with RuSr2EuCeCu2O10, which is a ferromagnetic (T-C similar to 150 K) insulator. Our results show that the rare earths, Eu and Ce, are in 3+ and 4+ states, respectively. Comparing the Ru core level spectra from these compounds to those from two Ru reference oxides, we also show that Ru in these ruthenocuprates is always in 5+ state, suggesting that the doped holes in the superconducting compound arising from the substitution of Ce4+ by Eu3+ are primarily in the Cu-O plane, in close analogy to all other doped high-T-C cuprates. Analysis of Cu 2p spectra in terms of a configuration interaction model provides a quantitative description of the gross electronic structures of these ruthenocuprates

Structural, Electrical and Magnetic Behaviour of FeTe0.5Se0.5 Superconductor

We report the synthesis as well as structural and physical properties of the bulk polycrystalline FeTe and FeTe0.5Se0.5 compounds. These samples are synthesised by the solid state-reaction method via vacuum encapsulation. Both studied compounds are crystallized in a tetragonal phase with space group P4/nmm. The parent FeTe compound shows an anomaly in resistivity measurement at around 78 K, which is due to the structural change along with a magnetic phase transition. The superconductivity in the FeTe0.5Se0.5 sample at 13 K is confirmed by the resistivity measurements. DC magnetisation along with an isothermal (M-H) loop shows that FeTe0.5Se0.5 possesses bulk superconductivity. The upper critical field is estimated through resistivity rho (T,H) measurements using Gingzburg-Landau (GL) theory and is above 50 T with 50 % resistivity drop criterion. The origin of the resistive transition broadening under magnetic field is investigated by thermally activated flux flow. The magnetic field dependence of the activation energy of the flux motion is discussed

Josephson coupling between superconducting clusters in Bi2Sr2CaCu2O8-delta crystals

Diamagnetic moments for two Bi2Sr2CaCu2O8+delta crystals were measured at different fields H and temperatures. For the higher fields two distinct transition temperatures T-g and T-J are seen, with T-g > T-J. By increasing H the line T-g(H) shifts very slowly while T-J(H) shifts much faster to lower temperatures, displaying a clear upward curvature well described by a theory based on Josephson coupling between superconducting clusters. We show further that T-J(H) is dependent on sample homogeneity, which is correlated with oxygen distribution in the high-T-c superconductors.51217418

Nano-Ni addition to MgB2: effects on the superconducting properties

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Samples of MgB2 pure phase, with Ni nanoparticles addition, were prepared using a solid diffusion reaction method. Clearly, the Ni nanoparticles act as effective pinning centers and enhance the critical current density values, especially for a sample with 0.5%Ni. A negligible amount of Ni diffuses inside the MgB2 grains, thus having a small effect on the transition temperature, which remains around 37.5 K.451849294933Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES

Local structural distortions and their role in superconductivity in SmFeAsO1-xFx superconductors

EXAFS studies at the As K edge as a function of temperature were carried out in SmFeAsO1-xFx (x = 0 and 0.2) compounds to understand the role of local structural distortions in superconductivity observed in F-doped compounds. A significant correlation between the thermal variation of local structural parameters such as anion height and superconducting onset is found in the fluorinated compounds. Such a variation in anion height is absent in the non-superconducting compound. An increase in the Fe-As bond distance just below the superconducting onset temperature indicates a similarity between the distortions observed in the high-T-C cuprates and these Fe-based superconductors

Superconducting and magnetic behaviour of niobium doped RuSr2Gd1.5Ce0.5Cu2O10-delta

Polycrystalline samples of Ru1-xNbxSr2Gd1.5Ce0.5Cu2O10-delta, 0 = 0.2, leading to changes in the magnetic hysteresis loops measured at low temperatures. These hysteresis loops can be explained as a result of the contribution of two distinct magnetic phases: the canted AFM phase and embedded Ru4+- rich clusters which order as a CG in low temperatures. Interestingly, the significant changes in the magnetic response of the material do affect the superconducting transition temperature Tc. It was found that both Tc and the superconducting fraction are reduced in samples which present the spin glass phase. Therefore, our results point to some coupling between magnetism and superconductivity in this ruthenocuprate family, the presence of the magnetic moment being deleterious for the superconductivity.191

Capacite de traitement de l'azote de la station d'epuration des eaux usees par biofiltration de Saltgourde (Communaute d'Agglomeration Perigourdine) : bilan des mesures realisees du 19 au 21 juin 2001

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