156 research outputs found

    The effect of Cr impurity to superconductivity in electron-doped BaFe2-xNixAs2

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    We use transport and magnetization measurements to study the effect of Cr-doping to the phase diagram of the electron-doped superconducting BaFe2-xNixAs2 iron pnictides. In principle, adding Cr to electron-doped BaFe2-xNixAs2 should be equivalent to the effect of hole-doping. However, we find that Cr doping suppresses superconductivity via impurity effect, while not affecting the normal state resistivity above 100 K. We establish the phase diagram of Cr-doped BaFe2-x-yNixCryAs2 iron pnictides, and demonstrate that Cr-doping near optimal superconductivity restore the long-range antiferromagnetic order suppressed by superconductivity.Comment: 10 pages, 5 figure

    Longitudinal spin excitations and magnetic anisotropy in antiferromagnetically ordered BaFe2As2

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    We report on a spin-polarized inelastic neutron scattering study of spin waves in the antiferromagnetically ordered state of BaFe2As2. Three distinct excitation components are identified, with spins fluctuating along the c-axis, perpendicular to the ordering direction in the ab-plane, and parallel to the ordering direction. While the first two "transverse" components can be described by a linear spin-wave theory with magnetic anisotropy and inter-layer coupling, the third "longitudinal" component is generically incompatible with the local moment picture. It points towards a contribution of itinerant electrons to the magnetism already in the parent compound of this family of Fe-based superconductors.Comment: 4 pages, 4 figures, plus Supplemental Materia

    Growth and post-annealing studies of La-Bi2201 single crystals

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    Bi2_2Sr2βˆ’x_{2-x}Lax_xCuO6+Ξ΄_{6+\delta} (0≀x≀\leq x \leq1.00) single crystals with high-quality have been grown successfully using the travelling-solvent floating-zone technique. The patterns of X-ray diffraction suggest high crystalline quality of the samples. After post-annealing in flowing oxygen at 600 o^oC, the crystals show sharp superconducting transitions revealed by AC susceptibility. The hole concentration pp is deduced from superconducting transition temperature (TcT_c), which exhibits a linear relation with La doping level xx. It ranges from the heavily overdoped regime (pβ‰ˆp \approx 0.2) to the extremely underdoped side (pβ‰ˆp \approx 0.08) where the superconductivity is absent. Comparing with the superconducting dome in Bi2+x_{2+x}Sr2βˆ’x_{2-x}CuO6+Ξ΄_{6+\delta} system, the effects from out-of-plane disorders show up in our samples. Besides the La doping level xx, the superconductivity is also sensitive to the content of oxygen which could be tuned by post-annealing method over the whole doping range. The post-annealing effects on TcT_c and pp for each La doping level are studied, which give some insights on the different nature between overdoped and underdoped regime.Comment: 6 pages, 6 figure
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