Inelastic neutron scattering measurements

In the oxygen-deficient compound YBa2Cu306.6, shows a broad maximum 

In this work we have used a spin-rotation-invariant SB approach to investigate magnetic and transport properties of the 2D t-t -/model. Our main results are the following (see also [81])  

Recently, our theory was improved to include (Gaussian) fluctuations beyond the paramagnetic saddle-point approximation [27, 80], We derived a concise expression for the spin susceptibility x q, co) of the - -/model which does not have the standard RPA form. Then we were able to show that the instability line obtained from a divergence of 0) is in agreement with the PM o spiral state phase boundary in the saddle-point phase diagram, which in fact proves the consistency of both approaches [27], 

For a recent overview of the experimental and theoretical situation see Proceedings of the Int. Conf M SHTSCIV, Grenoble 1994, in Physica C, 235-240 (1994) 

Proceedings of the Int. Euroconf. on Magnetic Correlations, Metal-Insulator-Ihansitions, and Superconductivity in Novel Materials, Nfmzhmg 1994, in J. Low. Temp. Phys., 3/4 (1995) 

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The Debye temperatures of stages two and one were determined by inelastic neutron scattering measurements [33], The total entropy variation using equation 8 is in the order of about 2 J/(mol.K). Although smaller in value, such variation accounts for 10-15% of the total entropy and should not be neglected. We are currently carrying on calculations of the vibrational entropy from the phonon density of states in LixC6 phases. 

In order to determine the dynamics of atoms we have to carry out an inelastic neutron scattering measurement. With a reactor source this can be done with a triple-axis spectrometer, which has an analyzer crystal. Tripleaxis refers to the three axes for the monochromator, sample, and analyzer, all moving independently and controlled by a computer. With a pulsed source we use a mechanical chopper, which is a rotating cylinder with a hole perpendicular to the rotating axis that allows neutrons with a chosen range of velocity to go through. The neutrons scattered by the sample are detected... 

Not any feature was observed in the single-magnon dispersion that would correlate with the lower-energy two-magnon peak in the inelastic neutron scattering measurements of the stripe-ordered nickelate Lai.69Sr0.3iNiC>4 also.311... 

In order to quantitatively reproduce the observed periodicity we included fourth-order terms in the spin Hamiltonian, Eq. (1), as employed in the simulation of inelastic neutron scattering measurements [45, 46] and performed a diagonalization of the [21x21] matrix describing the S = 10 system. For the calculation of the tunnel splitting we used D = 0.289 K, = 0.055 K [Eq. 1] and the fourth-order terms as defined in [45] with... 

Inelastic neutron scattering measurements are not trivial, and therefore the number of experimental studies of RUMs by this approach is few. The only single-crystal inelastic neutron scattering measurement has been on quartz (Dolino et al. 1992) and leucite, KA1S1206 (Boysen 1990). The RUMs for these two materials are shown in Table 1. 

We have performed a number of inelastic neutron scattering measurements from polycrystalline samples. The first measurements involved an average of the inelastic scattering over all values of the scattering vector Q, i.e. 

D.K. Ross, P.F. Martin, W.A. Oates R. Khoda Bakhsh (1979). Z. Phys. Chem., 114, 221-30. Inelastic neutron scattering measurements of optical vibration frequency distribution in hydrogen-metal systems. 

Fig. 18. Inelastic neutron scattering measurements exhibiting the variation of the cross section S(Q, to) of Ba rRujOc,...

In practice, one usually defines a training set of molecules and associated experimental properties and fits the relevant data with an assumed force field.The next step is to test the results on molecules and data outside the training set. Experimental data that depend on the energy surface and that may be used to determine the parameters of the intramolecular interactions consist mainly of gas-phase structural data derived from microwave spectra or electron diffraction patterns, crystal structures derived from X-ray and inelastic neutron scattering measurements, and vibrational frequencies obtained from infrared and Raman spectra. Torsional barriers are derived from NMR band shapes and relaxation times, whereas conformational energies are determined from spectroscopic and thermochemical data. Nonbonded parameters are determined mainly from... 

As described above, inelastic neutron scattering measures the energy that the system can exchange with the neutron and the probability of each exchange (see equation 6.5). Given that we are interested only in hydrogen, we can initially restrict ourselves to incoherent scattering, i.e. those terms in equation... 

If BD is so crucial, how do we know it exists and can we measure it quantitatively The existence of M - H2 a BD was definitively proven by inelastic neutron scattering measurements of a barrier to rotation of H2, which would not... 

The same study (Neville et al. 1996) also reports on inelastic neutron scattering measurements. They show spin wave excitation at low temperatures which, however, collapse into a diffusive response at 10 K (see in this connection also the discussion on USb). The 10 K point is clearly a special temperature but its exact nature remains enigmatic. But without doubt, this Kondo material exhibits most imusual spin d3mamical properties. Further studies are called for. 

The values of Swenson (1996) are selected since in combination with the heat capacity measurements of Gerstein et al. (1971) (6-350 K), Swenson (1996) gives representative equations of up to 350 K. The above value for the Debye temperature may be compared to 354.2 K calculated by Pleschiutschnig et al. (1991) from inelastic neutron scattering measurements. 

Fig. 30. Optical-phonon spectra from inelastic neutron scattering measurements on neptunium hydrides and deuterides. (a) Scattering law data for NpHj, 3 and NPD2.13. (b) Scattering lawdata for NpHj 55 at 90 K and room temperature. After Goldstone et al. (1989).

A. Incoherent inelastic neutron scattering measurements [53] gave some evidences that the boson peak is a localized mode on 6 and 11 monomers for PS and PB, respectively. Such localization was predicted in molecular dynamics simulations [54-56]. In the framework of the soft potential model, which will be mentioned later, the number of atoms participating in the boson peak mode was evaluated, showing the localization of the boson peak mode on several tens to hundreds of atoms for three inorganic glasses [28] and on several monomers for three polymers [57]. 

T >20 K. and this despite the sharpness of the phase transition as monitored by specifie heat or inelastic neutron scattering measurements in the same material. These and other observations have led to speculations that the weak antiferromagnetic order is not the primary order parameter of the transition (Broholm et al. 1991, Gorkov 1991, Ramirez et al. 1992, Barzykin and Gorkov 1993). 

It is tempting to identify the superfluid and normal fluid components of He II with the atoms of the condensate and excited states, respectively, of an ideal Bose-Einstein gas, but this, too, turns out to be a gross oversimplification. Nonetheless, it is clear that Bose-Einstein statistics do play an essential role in determining the properties of the liquid. If one calculates the Bose-Einstein condensation temperature of an ideal gas with the same density and atomic mass as liquid " He, one finds 7 3.1 K, and the difference between this value and 7 may plausibly be ascribed to the influence of the interatomic forces. The presence of a condensate of " He atoms in the zero momentum state has recently been confirmed by inelastic neutron scattering measurements. As shown in Fig. 14, the condensate fraction rises from zero at Tx towards an asymptotic limit of about 14% at low temperatures. This departure from the approximately 100% condensate characteristic of an ideal gas for r 7c is an expected consequence of the non-negligible interatomic forces. Of couse, as already noted in Fig. 13, the superfluid component does form 100% of the liquid at 7 = 0 and it cannot, therefore, be directly identified with the condensate fraction. 

The first inelastic neutron scattering measurements on polymers under strong states of thin film confinement were performed by Soles and co-workers on a variety of systems. In reality, these pioneering measurements were not truly inelastic in that they did not quantify the change in energy of the scattered neutrons. " Rather, they monitored confinement-induced changes in the elastic scattering intensity... 

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