Publications (10)0 Total impact
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ABSTRACT: Incoherent inelastic neutron scattering experiments were performed on Na 0.7 CoO2 and Na0.28 CoO2 1.3H2 O in order to understand how the dynamics of the hydrogen bond network of water is modified in the triangular crystalline lattice Na x CoO2 yH2 O. Using quasi elastic neutron scattering QENS we were able to differentiate between two types of proton dynamics a fast process due to water strongly bound into the sodium cobalt oxyhydrate structure during the hydration process and a slow process likely attributable to a collective motion . High resolution QENS experiments, carried out on Na0.28CoO2 1.3H2 O, show that at temperatures above 310 K the water dynamics can be well described by a random jump diffusion model characterized by a diffusion constant equal to 0.9.10?9 m2 s, which is significantly lower than the rate of diffusion for bulk water. Furthermore, our results indicate that at room temperature the sodium ions have no influence on the rotational dynamics of the fast water molecules.
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ABSTRACT: Abstract. Quasielastic neutron scattering QENS has been used to investigate the dynamical behaviour of H2O in the superconductor Na0.28CoO2.yH2O. The measurements were obtained at room temperature for a molar concentration of water, y 1.3. From the analysis of the Q dependence of the EISF and the line width we found that the water dynamics can be well described by jump rotations that take the molecule into identical orientation. We were also able to define a rotational correlation time of amp; 61556; 1.85ps
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R. Feyerherm,
E Dudzik,
A. U. B. Wolter,
S. Valencia,
O. Prokhnenko,
A. Maljuk,
S. Landsgesell,
N. Aliouane,
L Bouchenoire,
S Brown, D.N Argyriou
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ABSTRACT: X ray resonant magnetic scattering studies of rare earth magnetic ordering were performed on perovskite manganites RMnO3 R Dy, Gd in an applied magnetic field. The data reveal that the field induced three fold polarization enhancement for H a H approx. 20 kOe observed in DyMnO3 below 6.5 K is due to a re emergence of the Mn induced Dy spin order with propagation vector Dy Mn 0.385 b , which accompanies the suppression of the independent Dy magnetic ordering, Dy 1 2 b . For GdMnO3, the Mn induced ordering of Gd spins is used to track the Mn ordering propagation vector. The data confirm the incommensurate ordering reported previously, with Mn varying from 0.245 to 0.16 b on cooling from TMn N down to a transition temperature T0. New superstructure reflections which appear below T0 suggest a propagation vector Mn 1 4 b in zero magnetic field, which may coexist with the previously reported A type ordering of Mn. The Gd spins order with the same propagation vector below 7 K. Within the ordered state of Gd at T 1.8 K we find a phase boundary for an applied magnetic field H b, H 10 kOe, which coincides with the previously reported transition between the ground state paraelectric and the ferroelectric phase of GdMnO3. Our results suggest that the magnetic ordering of Gd in magnetic field may stabilize a cycloidal ordering of Mn that, in turn, produces ferroelectricity
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ABSTRACT: A first study of possible changes instigated by deuteration in amino acids was carried out using neutron diffraction, inelastic neutron scattering and Raman scattering in L alanine, C2H4 NH2 COOH. Careful analysis of the structural parameters shows that deuteration of L alanine engenders significant geometric changes as a function of temperature, which can be directly related to the observation of new lattice vibration modes in the Raman spectra. The combination of the experimental data suggests that C2D4 ND2 COOD undergoes a structural phase transition or a structural rearrangement at about 170 K. Considering that this particular amino acid is a hydrogen bonded system with short hydrogen bonds O H 1.8 , we evoke the Ubbelohde effect to conclude that substitution of hydrogen for deuterium gives rise to changes in the hydrogen bonding interactions. The structural differences suggest distinct relative stabilities for the hydrogenous and deuterated L alanine
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ABSTRACT: Synchrotron x ray diffraction and resonant magnetic scattering experiments on a single crystal of orthorhombic DyMnO3 have been carried out between 4 and 40 K. Below TN Dy 5 K, the Dy magnetic moments order in a commensurate structure with propagation vector 0.5 b . Simultaneous with the Dy magnetic ordering, an incommensurate lattice modulation with propagation vector 0.905 b evolves while the original Mn induced modulation is suppressed and shifts from 0.78 b to 0.81 b . This points to a strong interference of Mn and Dy induced structural distortions
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ABSTRACT: We present measurements of the thermal conductivity kappa and the thermal expansion alpha of NdMnO3 and TbMnO3. In both compounds, a splitting of the 4f multiplet of the R3 ion causes Schottky contributions to alpha. In TbMnO3 this contribution arises from a crystal field splitting, while in NdMnO3 it is due to the Nd Mn exchange coupling. Another consequence of this coupling is a strongly enhanced canting of the Mn moments. The thermal conductivity is greatly suppressed in both compounds. In TbMnO3, the main scattering process is resonant scattering of phonons between different energy levels of the 4f multiplets, whereas the complex 3d magnetism of the Mn ions is of minor importance. In NdMnO3, resonant phonon scattering on the 4f levels dominates at low temperature, while scattering on magnetic excitations becomes important at higher temperature
