Browsing by Author "Ivanov, AS"

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    Electron doping effects on the spin spectroscopy of BaFe2-xNixAs2 superconductors
    (International Conference on Neutron Scattering, 2017-07-12) Luo, HQ; Gong, DL; Xie, T; Lu, XY; Kamazawa, K; Iida, K; Kajimoto, R; Ivanov, AS; Adroja, DT; Kulda, J; Danilkin, SA; Deng, GC; Li, SL; Dai, PC
    High-temperature superconductivity in iron pnictides emerges from electron or hole doped parent compounds with antiferromagnetic order, which is argued to be associated with both the presence of high-energy spin excitations and a coupling between low-energy spin excitations and itinerant electrons. With more than 6 years\' efforts, we have used time-of-flight neutron spectroscopy to extensively map out the spin excitations in the electron-doped BaFe2-xNixAs2 especially around the overdoped zone boundary of superconductivity. We have found that the high energy spin fluctuations survive in the extremely high doping x=0.6 far beyond the superconducting dome, but the low energy spin excitations including the spin resonance mode is very sensitive to the electron dopings, by finally forming a large spin gap just after the disappearance of superconductivity in the overdoped regime. Further polarized neutron analysis indicate that the spin gap actually is anisotropic, and the longitudinal mode of spin fluctuations, as a hallmark of the itinerant magnetism from Fermi surface nesting, is totally eliminated together with the hole pockets near the electron-overdoped zone boundary of superconductivity.Our results suggest that the strong fluctuations from local moments give framework for magnetic interaction, while itinerant spin excitations originated from Fermi surface nesting are crucial to the superconductivity in iron pnictides.
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    Observation of the collective vibrational modes in Ni42Nb58 metallic glass
    (Elsevier, 2007-10-15) Syrykh, GF; Zemlyanov, MG; Ivanov, AS; Stride, JA; Lisichkin, YV; Khmenko, NA
    The dynamic structure factors, S(Q, E), for Ni42Nb58 metallic glass have been measured using neutron inelastic scattering on the IN4 spectrometer (ILL, Grenoble, France), over a range of momentum transfer, 0.7 < hQ/angstrom(-1) < 8, and energy transfer, 2 < E/meV < 50. Three samples with the same chemical composition and different Ni isotope content were investigated. The constant-E and constant-Q cuts through the S(Q, E) functions have been obtained. They reveal the E-and Q-dependencies due to the existence of the collective vibrational excitations in Ni42Nb58 glass. At the same time the difference of Ni and Nb atoms dynamics was observed by isotope contrast in the scattered spectra. © 2007, Elsevier Ltd.
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    Propagating vibrational modes in the Zr-Be metallic glasses
    (Institute of Physics, 2008-03-12) Syrykh, GF; Ivanov, AS; Klimenko, NA; Lisichkin, YV; Mutka, H; Stride, JA
    The dynamic structure factors, S(Q, E), for the Zr70Be30, Zr60Be40 and Zr50Be50 metallic glasses have been measured using neutron inelastic scattering on the IN4 spectrometer (ILL, Grenoble, France), over the range of momentum transfers 0.7 < h Q (angstrom(-1)) < 7 and energy transfers 2 < E (meV) < 60. The constant- Q cuts through the dynamic structure factor and longitudinal current correlation function, J(l) ( Q, E), were obtained. The dispersion relations for two representations, S( Q, E) and J(l) (Q, E), were derived by fitting a Gaussian to the peaks. The specific low-energy modes (similar to 5 meV) as well as 'acoustic-phonon like' (similar to 16 meV) and 'optic-phonon like' excitations (similar to 47 meV) were observed in these metallic glasses with disparate mass and ionic radius components. © 2008, Institute of Physics