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Mikhail V. Kovalchuk - One of the best experts on this subject based on the ideXlab platform.

  • Surface and bulk Contributions to x-ray thermal diffuse scattering (Green's function approach)
    Journal of Physics D: Applied Physics, 2001
    Co-Authors: S.a. Grigorian, I.a. Vartanyants, Mikhail V. Kovalchuk
    Abstract:

    The Green's function formalism is applied to the analysis of the Surface Contribution to the inelastic scattering of x-rays by acoustic modes of thermal excitations in a crystal. It is shown that the Surface Contribution to thermal diffuse scattering (TDS) near the Surface can become comparable to and can even exceed the volume Contribution. The same formalism is applied to the investigation of TDS in the case of dynamical diffraction, when an x-ray standing wave is generated in a crystal. TDS yield curves calculated according to this model show good agreement with the experimental results.

  • Surface Contribution to inelastic scattering of X-rays on thermal phonons
    physica status solidi (b), 2001
    Co-Authors: I.a. Vartanyants, S.a. Grigorian, Mikhail V. Kovalchuk
    Abstract:

    The Green's function formalism is applied to the analysis of the Surface Contribution to the inelastic scattering of X-rays by acoustic modes of thermal excitations in a crystal. Crystals with a cubic unit cell are analysed. It is shown that the Surface Contribution to thermal diffuse scattering (TDS) near the Surface can become comparable to and even can exceed the volume one. The same general formalism is applied to the investigation of TDS in the case of dynamical diffraction, when an X-ray standing wave is generated in the crystal.

H. S. Lee - One of the best experts on this subject based on the ideXlab platform.

  • Surface Contribution to the superconducting properties of MgB2 single crystals
    Physical Review B, 2003
    Co-Authors: Andreas Rydh, Ulrich Welp, Jon Hiller, Alexei Koshelev, W. K. Kwok, George W. Crabtree, K. H. Kim, Chang Uk Jung, H. S. Lee
    Abstract:

    We demonstrate direct evidence of possible Surface superconductivity on small, well-shaped ${\mathrm{MgB}}_{2}$ single crystals. Transport measurements in the range $Hl{1.6H}_{c2}^{c},$ where ${H}_{c2}^{c}$ is the bulk upper critical field for the c axis, show non-Ohmic and strongly angular-dependent resistivity. Studies of the alignment of $\mathbf{H}$ with selected crystal Surfaces, transport and specific heat measurements on the same crystal, and a physical sculpturing of the crystal Surfaces using a focused ion beam all support the conclusion. Similar, albeit less pronounced results are obtained for fields in the basal plane.

K. H. Kim - One of the best experts on this subject based on the ideXlab platform.

  • Surface Contribution to the superconducting properties of MgB2 single crystals
    Physical Review B, 2003
    Co-Authors: Andreas Rydh, Ulrich Welp, Jon Hiller, Alexei Koshelev, W. K. Kwok, George W. Crabtree, K. H. Kim, Chang Uk Jung, H. S. Lee
    Abstract:

    We demonstrate direct evidence of possible Surface superconductivity on small, well-shaped ${\mathrm{MgB}}_{2}$ single crystals. Transport measurements in the range $Hl{1.6H}_{c2}^{c},$ where ${H}_{c2}^{c}$ is the bulk upper critical field for the c axis, show non-Ohmic and strongly angular-dependent resistivity. Studies of the alignment of $\mathbf{H}$ with selected crystal Surfaces, transport and specific heat measurements on the same crystal, and a physical sculpturing of the crystal Surfaces using a focused ion beam all support the conclusion. Similar, albeit less pronounced results are obtained for fields in the basal plane.

Régine Perzynski - One of the best experts on this subject based on the ideXlab platform.

  • Superparamagnetic relaxation evidences large Surface Contribution for the magnetic anisotropy of MnFe204 nanoparticles of ferrofluids
    Journal of Materials Science, 2007
    Co-Authors: Carlucio Roberto Alves, F A Tourinho, Jérôme Depeyrot, R. Aquino, Emmanuelle Dubois, Régine Perzynski
    Abstract:

    Manganese ferrite nanoparticles, in the size range 3.3–9.0 nm, are prepared by a hydrothermal coprecipitation process and peptized in aqueous solution. The magnetization curves recorded at room temperature on diluted colloidal sols allow characterizing the distribution of magnetic moment by using a simple Langevin formalism. Mossbauer spectroscopy measurements performed on powder samples at 77 K exhibit a quadrupolar doublet which intensity grows at the expense of the hyperfine sextet pattern as the nanoparticles mean size decreases. The magnetic dynamics behavior is then investigated by measurements of magnetic hysteretic properties at 5 K and temperature dependence of the zero field cooling (ZFC) susceptibility. The values found for the effective anisotropy constant and the dependence of the irreversibility field, inversely proportional to the reference size, clearly indicate that the magnetic anisotropy of our nanoparticles finds its origin on the disordered Surface layer.

  • In-field Mössbauer study of the disordered Surface Contribution in nickel ferrite nanomagnets
    Journal of Magnetism and Magnetic Materials, 2007
    Co-Authors: E. C. Sousa, Marcelo Henrique Sousa, Hercílio R. Rechenberg, Gerardo F. Goya, F A Tourinho, Régine Perzynski, Jérôme Depeyrot
    Abstract:

    Abstract Mossbauer measurements on NiFe 2 O 4 nanoparticles at 4.2 K in the presence of an applied external magnetic field ranging up to 12 T are reported. Three distinct Contributions of the spectra are found: two corresponding to Fe ions at A and B sites of the ferrimagnetic core with spins collinearly aligned to the field and a third one originating from misaligned Surface spins. The volume fraction of the latter decreases for increasing field concomitantly with a slow decrease in mean canting angle.

P. Van Isacker - One of the best experts on this subject based on the ideXlab platform.

  • The symmetry energy in nuclei and in nuclear matter
    The European Physical Journal A, 2007
    Co-Authors: A.e.l. Dieperink, P. Van Isacker
    Abstract:

    We discuss to what extent information on ground-state properties of finite nuclei (energies and radii) can be used to obtain constraints on the symmetry energy in nuclear matter and its dependence on the density. The starting point is a generalized Weizsäcker formula for ground-state energies. In particular, effects from the Wigner energy and shell structure on the symmetry energy are investigated. Strong correlations in the parameter space prevent a clear isolation of the Surface Contribution. Use of neutron skin information improves the situation. The result of the analysis appears consistent with a rather soft density dependence of the symmetry energy in nuclear matter.

  • The symmetry energy in nuclei and in nuclear matter
    International Journal of Modern Physics E, 2006
    Co-Authors: P. Van Isacker, A.e.l. Dieperink
    Abstract:

    We discuss to what extent information on ground-state properties of finite nuclei (energies and radii) can be used to obtain constraints on the symmetry energy in nuclear matter and its dependence on the density. The starting point is a generalized Weizsäcker formula for ground-state energies. In particular effects from the Wigner energy and shell structure on the symmetry energy are investigated. Strong correlations in the parameter space prevent a clear isolation of the Surface Contribution. Use of neutron skin-information improves the situation. We find that inclusion of the Wigner effect leads to a larger value of the symmetry energy of nuclear matter at the saturation point.