47 research outputs found

    Dynamical coherent-potential approximation approach to excitation spectra in 3d transition metals

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    First-principles dynamical CPA (Coherent-Potential Approximation) for electron correlations has been developed further by taking into account higher-order dynamical corrections with use of the asymptotic approximation. The theory is applied to the investigations of a systematic change of excitation spectra in 3d3d transition metals from Sc to Cu at finite temperatures. It is shown that the dynamical effects damp main peaks in the densities of states (DOS) obtained by the local density approximation to the density functional theory, reduce the band broadening due to thermal spin fluctuations, create the Mott-Hubbard type bands in the case of fcc Mn and fcc Fe, and create a small hump corresponding to the `6 eV' satellite in the case of Co, Ni, and Cu. Calculated DOS explain the X-ray photoelectron spectroscopy data as well as the bremsstrahlung isochromat spectroscopy data. Moreover, it is found that screening effects on the exchange energy parameters are significant for understanding the spectra in magnetic transition metals.Comment: To be published in Phys. Rev.

    Sigma-phase in Fe-Cr and Fe-V alloy systems and its physical properties

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    A review is presented on physical properties of the sigma-phase in Fe-Cr and Fe-V alloy systems as revealed both with experimental -- mostly with the Mossbauer spectroscopy -- and theoretical methods. In particular, the following questions relevant to the issue have been addressed: identification of sigma and determination of its structural properties, kinetics of alpha-to-sigma and sigma-to-alpha phase transformations, Debye temperature and Fe-partial phonon density of states, Curie temperature and magnetization, hyperfine fields, isomer shifts and electric field gradients.Comment: 26 pages, 23 figures and 83 reference

    Nouveaux appareils pour l'étude des transformations des alliages microdilatomètre isotherme. Thermomagnétomètre enregistreur

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    L'auteur décrit deux appareils créés au laboratoire des Aciéries d'Imphy pour l'étude des alliages. Le microdilatomètre, destiné à l'analyse des réactions d'instabilité des alliages traités ou écrouis, enregistre, en fonction du logarithme du temps, la variation spontanée de longueur d'un échantillon maintenu à température constante. Dans beaucoup de cas, les courbes sont quasi rectilignes : leur coefficient angulaire est adopté comme indice d'instabilité de l'alliage. Le thermomagnétomètre enregistre, en fonction de la température, les variations d'aimantation des corps ferromagnétiques. Les diagrammes sont tracés par le jeu d'un seul miroir mobile autour de deux axes rectangulaires. L'appareil, insensible aux trépidations et aux perturbations du champ terrestre — qualités importantes dans une usine sidérurgique —, donne des courbes très nettes, sur lesquelles les moindres anomalies thermomagnétiques ressortent sans ambiguité

    A Phase Transition in Phenanthrene Crystal

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    CV. The mechanism of rolling friction

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    Volume Magnetostriction in Nickel-Iron Alloys

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    Genaue potentiometrische Manganbestimmung

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