265 research outputs found
La contamination perçue des produits : vers une meilleure compréhension de ses antécédents et de ses effets
CAHIER DE RECHERCHES n° 2012-05 E3L'avènement des produits en libre-service conduit les consommateurs à exercer davantage leur sens tactile. Si les recherches en marketing sensoriel ont montré l'intérêt de laisser les consommateurs manipuler librement les produits, il convient de nuancer ce constat. De récentes recherches se sont intéressées aux aspects négatifs du toucher et plus spécifiquement à la perception de contamination des produits. L'objectif de ce papier est de mieux cerner le phénomène de contamination. Des entretiens semi-directifs permettent de mettre en évidence les réponses d'ordre émotionnel, cognitif et comportemental suscitées lorsqu'un consommateur se retrouve confronté à un produit déjà manipulé
Spin gaps and magnetic structure of NaxCoO2
We present two experiments that provide information on spin anisotropy and
the magnetic structure of NaxCoO2. First, we report low-energy neutron
inelastic scattering measurements of the zone-center magnetic excitations in
the magnetically ordered phase of Na0.75CoO2. The energy spectra suggest the
existence of two gaps, and are very well fitted by a spin-wave model with both
in-plane and out-of-plane anisotropy terms. The gap energies decrease with
increasing temperature and both gaps are found to have closed when the
temperature exceeds the magnetic ordering temperature T_m~22 K. Secondly, we
present neutron diffraction studies of Na0.85CoO2 with a magnetic field applied
approximately parallel to the c axis. For fields in excess of ~8T a magnetic
Bragg peak was observed at the (0,0,3) position in reciprocal space. We
interpret this as a spin-flop transition of the A-type antiferromagnetic
structure, and we show that the spin-flop field is consistent with the size of
the anisotropy gap.Comment: 9 pages, 7 figure
Influence of static Jahn-Teller distortion on the magnetic excitation spectrum of PrO2: A synchrotron x-ray and neutron inelastic scattering study
A synchrotron x-ray diffraction study of the crystallographic structure of
PrO2 in the Jahn-Teller distorted phase is reported. The distortion of the
oxygen sublattice, which was previously ambiguous, is shown to be a chiral
structure in which neighbouring oxygen chains have opposite chiralities. A
temperature dependent study of the magnetic excitation spectrum, probed by
neutron inelastic scattering, is also reported. Changes in the energies and
relative intensities of the crystal field transitions provide an insight into
the interplay between the static and dynamic Jahn-Teller effects.Comment: 7 pages, 6 figure
Magnetic order and dynamics of the charge-ordered antiferromagnet La1.5Sr0.5CoO4
We describe neutron scattering experiments performed to investigate the
magnetic order and dynamics of half-doped La1.5Sr0.5CoO4. This layered
perovskite exhibits a near-ideal checkerboard pattern of Co2+/Co3+ charge order
at temperatures below ~ 800 K. Magnetic correlations are observed at
temperatures below ~ 60 K but static magnetic order only becomes established at
31 K, a temperature at which a kink is observed in the susceptibility. On
warming above 31 K we observed a change in the magnetic correlations which we
attribute either to a spin canting or to a change in the proportion of
inequivalent magnetic domains. The magnetic excitation spectrum is dominated by
an intense band extending above a gap of approximately 3 meV up to a maximum
energy of 16 meV. A weaker band exists in the energy range 20-30 meV. We show
that the excitation spectrum is in excellent quantitative agreement with the
predictions of a spin-wave theory generalized to include the full magnetic
degrees of freedom of high-spin Co2+ ions in an axially distorted crystal
field, coupled by Heisenberg exchange interactions. The magnetic order is found
to be stabilized by dominant antiferromagnetic Co2+ -- Co2+ interactions acting
in a straight line through Co3+. No evidence is found for magnetic scattering
from the Co3+ ions, supporting the view that Co3+ is in the S = 0 state in this
material.Comment: 17 pages, 10 figures. Accepted for publication in Phys. Rev.
A critical assessment of the pairing symmetry in NaxCoO2.yH2O
We examine each of the symmetry-allowed pairing states of NaxCoO2.yH2O and
compare their properties to what is experimentally and theoretically
established about the compound. In this way, we can eliminate the vast majority
of states that are technically allowed and narrow the field to two, both of
f-wave type states. We discuss the expected features of these states and
suggest experiments that can distinguish between them. We also discuss
odd-frequency gap pairing and how it relates to available experimental
evidence
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