Search results for "inelastic"
showing 10 items of 700 documents
Inelastic neutron and low-frequency Raman scattering in niobium-phosphate glasses: the role of spatially fluctuating elastic and elasto-optic constan…
2011
We investigate the low-frequency enhancement of vibrational excitations ('boson peak') in niobium-phosphate glasses through the combination of inelastic neutron and polarization-resolved Raman scattering. The spectra of these glasses reveal an enhancement of the vibrational density of states and of the cross section for spontaneous Raman scattering in the frequency range below 150?cm ? 1. A recent theoretical model that is based on fluctuating elastic and elasto-optic (Pockels) constants provides a unified description of the measured neutron and Raman spectra, including the depolarization ratio.
Polyoxometalates: From Magnetic Models to Multifunctional Materials
2002
In this article we have presented some recent achievements of the polyoxometalates in the fields of molecular magnetism and functional molecular materials. In the context of the molecular magnetism we have shown that POMs provide ideal examples of magnetic clusters with coexisting ferro and antiferromagnetic exchange interactions which can be investigated using a variety of magnetic techniques, including the Inelastic Neutron Scattering spectroscopy, to get a thorough characterization of the magnetic levels in these large clusters, and to test the validity of the spin hamiltonians commonly used in magnetism.
Spin-polarization effects for electrons passing through thin iron and cobalt films
1993
Abstract Spin-dependent effects of the inelastic mean free path (IMFP) are evident for low-energy electrons passing through magnetized ferromagnetic films caused by a different attenuation within the layer. Values of IMFP for both spin components were determined for ultrathin iron and cobalt layers on W(1 1 0) by means of spin-resolving photoelectron spectroscopy.
Vibrational properties of 1D- and 3D polynuclear spin crossover Fe(II) urea-triazoles polymer chains and quantification of intrachain cooperativity
2020
Abstract The vibrational dynamics of the iron centres in 1D and 3D spin crossover Fe(II) 4-alkyl-urea triazole chains have been investigated by synchrotron based nuclear inelastic scattering. For the 1D system, the partial density of phonon states has been modelled with density functional theory methods. Furthermore, spin dependent iron ligand distances and vibrational modes were obtained. The previously introduced intramolecular cooperativity parameter H coop (Rackwitz et al, Phys. Chem. Chem. Phys. 2013, 15, 15450) has been determined to −31 kJ mol−1 for [Fe(n-Prtrzu)3(tosylate)2] and to +27 kJ mol−1 for [Fe(n-Prtrzu)3(BF4)2]. The change of sign in H coop is in line with the incomplete an…
Time-Dependent Correlation and Response Functions
2014
The dynamics of liquids is discussed with the help of time-dependent correlation functions. They are related to response functions by the fluctuation-dissipation theorem. This theorem enables to relate experimentally measured inelastic scattering data to the Fourier-transformed correlation and response functions. The Laplace transform of the correlation functions can be represented as a continuous fraction with suitable residual terms (memory functions). The projection formalism of Mori and Zwanzig is introduced.
Statics and Dynamics of a Glassy Crystal: A NMR- and Neutron Scattering Investigation of (NaCl) 0.35 (NaCN) 0.65
1987
The statics and the dynamics of the glass transition in (NaCl)0.35(NaCN)0.65 have been investigated by inelastic neutron scattering and are directly compared to NMR results. Insight into the relaxation dynamics is gained via the temperature dependence of the transverse acoustic phonon modes and via the spin relaxation time T1. The statics of the system is reflected by the growth of a central peak and by the distribution of electric-field gradients. Both quantities are directly related to the glass order parameter. The temperature dependence of the order parameter provides experimental evidence that in NaCl:NaCN mixed crystals the glass transition is dominated by random fields rather than by…
Crystal Fields in PrX3 (X=In, Tl, Pb, Sn) Intermetallic Compounds with Cu3Au Structure
1977
We have determined the crystal field splittings of Pr3+ in PrIn3, PrTl3, PrPb3, and PrSn3 by inelastic neutron scattering. The values of the deduced crystal field parameters are found to depend strongly on the constituent X, though all systems have nonmagnetic ground-states. The line widths in the different systems are compared.
Coupled rotational and translational modes in the mixed molecular crystal KBr1?x (CN) x
1980
TheE g andT 2g acoustic phonon modes of the molecular crystals KBr0.96(CN)0.04 and KBr0.86(CN)0.14 have been investigated by inelastic neutron scattering at 6, 90 and 300 K. Clear resonances due to mode-mode coupling to molecular excitations were observed. In complementary ultrasonic experiments the elastic constants were found to pass through minima as a function of temperature. The results were quantitavely explained by a model which assumes simple forms of the molecular excitation spectrum. An alternative interpretation, though being only qualitative, postulates a freezing of the CN molecules into a glass-like phase.
Crystal Fields in Pr-Hydrides
1977
Inelastic neutron scattering was used to determine the crystal field splittings of PrD2 and PrD2.5. For the PrD2 crystal field at the Pr-site is cubic and can be explained by a negative charge of the hydrogen. The splitting observed for PrD2.5 can be described assuming a well defined short range order caused by a mer-configuration of the half filled octahedral hydrogen sites leading to an orthorhombic crystal field. The structure and the paramagnetic susceptibility of the Pr-hydrides are discussed on this basis.
Crystal field splitting of some rare earth intermetallic compounds with Cu3Au structure
1980
Inelastic neutron scattering studies were performed in the paramagnetic phases of several rare earth compounds that crystallize in the cubic Cu3Au structure: ErPb3, ErTl3, ErIn3, HoPb3, HoTl3, HoIn3, PrSn3, PrPb3, PrTl3, PrIn3, CeIn3, La1−c Pr c Tl3, and Pr(In0.5Tl0.5)3. The energies, widths and intensities of the crystal field excitations are determined and discussed in terms of interactions between the rare earth ions. Variations of the crystal field parameters are observed across the series.