Biomedical subjects

A Stunault

Publications and source records attributed to A Stunault.

5 recordsLinked to original sources

PubMed2006

Spin-liquid correlations in the Nd-langasite anisotropic kagomé antiferromagnet.

Dynamical magnetic correlations in the geometrically frustrated Nd(3)Ga(5)SiO(14) compound were probed by inelastic neutron scattering on a single crystal. A scattering signal with a ring shape distribution in reciprocal space and unprecedented dispersive features was discovered. Comparison with calculated static magnetic scattering from models of correlated spins suggests that the observed phase is a spin liquid inherent to an antiferromagnetic kagomé-like lattice of anisotropic Nd moments.

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PubMed2005

Spin excitations in an anisotropic bond-alternating quantum s = 1 chain in a magnetic field: contrast to haldane spin chains.

Inelastic neutron scattering experiments on the S = 1 quasi-one-dimensional bond-alternating antiferromagnet Ni(C9D24N4)(NO2)ClO4 have been performed under magnetic fields below and above a critical field Hc at which the energy gap closes. Normal field dependence of Zeeman splitting of the excited triplet modes below Hc has been observed, but the highest mode is unusually small and smears out with increasing field. This can be explained by an interaction with a low-lying two magnon continuum at q(parallel) = pi that is present in dimerized chains but absent in uniform ones. Above Hc, we find only one excited mode, in stark contrast with three massive excitations previously observed in the structurally similar Haldane-gap material NDMAP [A. Zheludev, Phys. Rev. B 68, 134438 (2003)].

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PubMed2001

The XMaS beamline at ESRF: instrumental developments and high-resolution diffraction studies.

The beamline, which is situated on a bending magnet at ESRF, comprises a unique combination of instrumentation for high-resolution and magnetic single-crystal diffraction. White-beam operation is possible, as well as focused and unfocused monochromatic modes. In addition to an eleven-axis Huber diffractometer, which facilitates simple operation in both vertical and horizontal scattering geometries, there is an in-vacuum polarization analyser and slit system, mirrors for harmonic rejection, sub 4.2 K and 1 Tesla magnetic field sample environment, plus a diamond phase plate for polarization conditioning. The instrumentation developed specifically for this beamline is described, and its use illustrated by recent scientific results.

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PubMed2001

Resonant enhancements at nonmagnetic ions: new possibilities for magnetic X-ray scattering.

Synchrotron experiments with uranium antiferromagnetic compounds have discovered large ( >1000) enhancements of the magnetic scattering intensities at the K edges of nominally nonmagnetic anions, e.g., Ga and As. The width in energy, the position with respect to the white line, and the azimuthal and polarization dependencies permit one to associate the signal with transitions of E1 dipole symmetry from 1s to 4p states. In momentum space, the signal exhibits long-range order at the antiferromagnetic wave vector. We discuss possible channels capable of generating the observed enhancements.

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PubMed1998

Polarization analysis in the 3-25 keV range at the ESRF magnetic scattering beamline.

The ESRF magnetic scattering beamline has been optimized for easy tunability of the polarization and energy in the 3-40 keV range. The linear horizontal polarization from the undulator reaches 99.9%, with a flux of approximately 10(12) photons s(-1) at the sample. The diffractometer can operate in horizontal and vertical geometries, with an energy or polarization analyser. The capabilities of this beamline in terms of flux, energy tunability and polarization, permitted polarization analysis of resonant magnetic scattering from antiferromagnetic UPd(2)Si(2) at both the L(2)- and M(4)-edges of uranium, to separate the contributions of the 5f and 6d electrons to the magnetism.

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