No abstract available

[en] By the use of the newly developed neutron spin echo method neutron scattering studies of elementary excitations can now, for the first time, be extended to the μeV resolution range. The first such experiment is described, and its results are shown to complement substantially previous knowledge on the temperature dependence of the energy and lifetime of the roton excitation and the suggested onset of three phonon decay beyond the roton minimum in superfluid ⁴He. (author)

[en] The Workshop on Probing Frontiers in Matter with Neutron Scattering consisted of a series of lectures and discussions about recent highlights in neutron scattering. In this report, we present the transcript of the concluding discussion session (wrap-up session) chaired by John C. Browne, Director of Los Alamos National Laboratory. The workshop had covered a spectrum of topics ranging from high T_c superconductivity to polymer science, from glasses to molecular biology, a broad review aimed at identifying trends and future needs in condensed matter research. The focus of the wrap-up session was to summarize the workshop participants' views on developments to come. Most of the highlights presented during the workshop were the result of experiments performed at the leading reactor-based neutron scattering facilities. However, recent advances with very high power accelerators open up opportunities to develop new approaches to spallation technique that could decisively advance neutron scattering research in areas for which reactor sources are today by far the best choice. The powerful combination of neutron scattering and increasingly accurate computer modeling emerged as another area of opportunity for research in the coming decades

[en] Neutron spin echo (NSE) experiments were performed on polycrystalline samples of Eu/sub x/Sr/sub 1-x/S for x = 0.4 and 0.54 in the temperature range of 1.2 < T < 10K and for 0.036 < Q < .18 A^-1. The x = 0.4 sample exhibits a paramagnetic (PM) to spin glass (SG) transition near T/sub f/ approx. 2K. In the x = 0.54 sample, large ferromagnetic correlations develop below 5K and a spin-glass state appears at lower temperatures. In the NSE experiment, the spin-spin correlation function, S(Q,t), is measured directly for times between .03 < t < 5 ns. At low temperatures both materials exhibit a weak Q dependence in the dynamics and the spins are essentially frozen over the time range explored. On heating the x = 0.4 sample the spins start to fluctuate more rapidly, but no dramatic change occurs around T/sub f/. On heating the x = 0.54 sample, S (Q,t) decreases rapidly with time. Near the 5K, S(Q,t) is exponential (e/sup -GAMMA t/) with GAMMA being strongly Q dependent. Measurements of the depolarization of the scattered beam confirms the absence of true long range ferromagnetic order below T/sub c/

[en] High-reflectivity supermirrors allow for sophisticated neutron optical systems working with multiple reflections (for example polarising cavities and beam splitters). Polarising cavities are highly efficient broad-wavelength band-polariser systems. Beam-splitter polarising cavities, for example, yield a practically ideal separation into one spin 'up' and one spin 'down' neutron beam, which can supply two different instruments. This later principle was already implemented at BENSC. Monte Carlo simulations were recently done to optimise polarising cavity systems and to search for possible new applications at ESS. Wavelength-dependent polarisation intensities were computed with ESS moderators

[en] In recent applications of neutron scattering the dynamic range is found to be an important aspect of instrument performance along with neutron flux and resolution. It is pointed out that due to the inherent use of a broad wavelength band, certain instruments, like small angle scattering and neutron spin echo spectrometers, provide better dynamic range capability on a pulsed source than on a continuous source

[en] In situ fast kinetic ellipsometry, X-ray and polarized neutron scattering are used to investigate the growth of sputtered Fe₈₉Co₁₁-Si multilayers with atomic resolution and to determine interface thickness and composition. The values of these properties depend on the sputtering parameters. Under the conditions of minimal thickness of the interface layers we find on top of the silicon layer 15 A (Fe₈₉Co₁₁)_0.5Si_0.5 and on top of the iron cobalt layer 19 A (Fe₈₉Co₁₁)_0.67Si_0.33. During the growth of the iron cobalt layer a phase transition occurs. After the formation of the interface layer on top of the silicon layer the iron cobalt alloy starts to grow in an amorphous phase until a thickness of 25 A is reached. Then it crystallizes down to the interface layer whereby it shrinks to 18.5 A, the atomic density changes nearly proportionally to the imaginary part of the index of refraction. As will be shown, the growth of the layers and the formation of the interface layers can be followed on an atomic scale

No abstract available

[en] The additional spin degree of freedom of the neutron can be made use of in neutron scattering work in two fundamental ways: (a) directly for the identification of magnetic scattering effects and (b) indirectly as a spectroscopic tool for modulating and analysing beams. Although strong magnetic scattering contributions can often be studied by unpolarized neutrons, a fully unambiguous separation of nuclear and magnetic phenomena can only be achieved by the additional information provided by polarized neutrons, especially if one of the two kinds of contributions is weak compared to the other. In the most general case a sample with both magnetic and nuclear features can be characterized by as many as 16 independent dynamic correlation functions instead of the single well known S(q, ω) for non-magnetic nuclear scattering only. Polarization analysis in principle allows one to determine all these 16 functions. The indirect applications of polarized neutrons are also steadily gaining importance. The most widely used method of this kind, the application of Larmor precessions for high resolution energy analysis in Neutron Spin Echo spectroscopy opened up a whole new domain in inelastic neutron scattering which was not accessible to any other spectroscopic method with or without neutrons before. (author)

[en] The thickness dependence of interface layers in FeCo-Si multilayers on sputtering voltage, argon pressure and substrate bias potential was examined. The multilayers were characterised by in situ kinetic ellipsometry, X-ray reflection, X-ray diffraction, polarized neutron reflection and atomic force microscopy. A minimum thickness for the sum of both interface layers per period between 23 A and 24 A was found for different combinations of production parameter values. For an argon pressure of 1.3x10^-3 mbar the minimum interface thickness was found at a sputtering voltage of 708 V, and for an argon pressure of 2.3x10^-3 mbar at 880 V. These values were determined for a floating substrate potential of approximately +60 V relative to ground. Applying a substrate bias potential of -70 V the minimum interface thickness occurred for a sputtering voltage of 880 V at an argon pressure of 1.3x10^-3 mbar. This study confirmed the results of the former empirical optimisation. By revealing the existence of several sets of optimum parameters it opens up a further parameter to adjust other properties like stress. The interface layer on top of the FeCo layer is 16% thicker than the one on top of the Si layer due to the larger roughness of the FeCo layers