A. Hiess

Multipolar, magnetic, and vibrational lattice dynamics in the low-temperature phase of uranium dioxide

We report the results of inelastic neutron scattering experiments performed with triple-axis spectrometers to investigate the low-temperature collective dynamics in the ordered phase of uranium dioxide. The results are in very good agreement with the predictions of mean-field random phase approximation calculations, emphasizing the importance of multipolar superexchange interactions. By comparing neutron scattering intensities in different polarizationchannelsandatequivalentpointsindifferentBrillouinzones,weshowthemixedmagnetovibrationalquadrupolar character of the observed excitations. The high-energy resolution afforded by the cold triple-axis spectrometer allowed us to study in detail the magnon-phonon interaction giving rise to avoided crossings along the [00ξ] reciprocal space direction.

Magnetization dynamics in the normal and superconducting phases of UPd2Al3: I. Surveys in reciprocal space using neutron inelastic scattering

This topical review presents results from neutron inelastic scattering experiments on single crystals of UPd2Al3. The focus is on the experimental situation, while the sequel paper advances theoretical perspectives. We present a detailed and complete characterization of the wavevector- and energy-dependent magnetization dynamics in UPd2Al3 as measured by neutron inelastic scattering primarily in the form of extensive surveys in energy–momentum space under a wide range of experimental conditions, and put our observations in context with data that has been published previously by two independent groups. In this way we emphasize the robustness of the results, which indicate the intricate nature of the dynamic magnetic susceptibility of this material. This study yields unique insight into the low-temperature ground state, which exhibits a microscopic coexistence of antiferromagnetism and superconductivity, making UPd2Al3 one of the most accessible heavy-fermion superconductors that can be fully characterized by neutron spectroscopy.

ILLs renewed thermal three-axis spectrometer IN8C

Abstract ILLs first fully-optimised high-flux thermal-neutron three-axis spectrometer IN8C is now being built and will be operational in the year 2000. In this paper we summarise the characteristics of this instrument, rehearse its expected performance and outline several technical details.

Role of vibrational entropy in the stabilization of the high-temperature phases of iron

The phonon dispersions of the bcc and fcc phases of pure iron ({\alpha}-Fe, {\gamma}-Fe and {\delta}-Fe) at ambient pressure were investigated close to the respective phase transition temperatures. In the open bcc structure the transverse phonons along T1 [{\xi}{\xi}0] and T1 [{\xi}{\xi}2{\xi}] are of particularly low energy. The eigenvectors of these phonons correspond to displacements needed for the transformation to the fcc {\gamma}-phase. Especially these phonons, but also all other phonons soften considerably with increasing temperature. Comparing thermodynamic properties of the fcc and the two bcc phases it is shown that the high temperature bcc phase is stabilized predominantly by vibrational entropy, whereas for the stabilization of the fcc phase electronic entropy provides an equal contribution.

ThALES—three axis low energy spectroscopy at the Institut Laue–Langevin

Building on the strength of the present cold neutron three-axis spectrometer IN14, but using state-of-the-art neutron optics, we conceived the next generation three-axis instrument for low energy spectroscopy (ThALES) at the Institut Laue–Langevin (ILL). The main aims of the new instrument are: (i) to increase the overall data collection rate by rebuilding the neutron optics of the primary spectrometer achieving a higher incident neutron flux as well as by multiplexing the analyser–detector system, (ii) to provide an efficient and easy-to-use polarized neutron option, (iii) to extend the incident neutron range towards higher energies bridging the gap with thermal instruments, and (iv) to be able to use high-field magnets—such as the currently available 15 T cryomagnet—under all possible experimental conditions, i.e. in a wider range of incident energies. The expected increase in count rate by at least one order of magnitude allows for new experiments such as high pressure experiments on small sample sizes or investigations of magnetic excitations in thin films. Polarized inelastic neutron measurements should equal count rates of the present IN14 in unpolarized mode. The implementation of various optical elements enhances the flexibility of the instrument and allows trading momentum resolution for high neutron intensity.

Magnetic Excitations in NpCoGa5 - Inelastic Neutron Scattering Experiments

We report the results of inelastic neutron scattering experiments on NpCoGa

Magnetization dynamics in the normal and superconducting phases of UPd2Al3: II. Inferences on the nodal gap symmetry

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Magnetic excitations in UGa3

, an isostructural analogue of the PuCoGa

Monte Carlo simulation of neutron fluxes on an absolute scale – comparison to experiments

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Optimizing Monochromatic Focusing on ThALES

superconductor. Two energy scales characterize the magnetic response in the antiferromagnetic phase. One is related to a non-dispersive excitation between two crystal field levels. The other at lower energies corresponds to dispersive fluctuations emanating from the magnetic zone center. The fluctuations persist in the paramagnetic phase also, although weaker in intensity. This supports the possibility that magnetic fluctuations are present in PuCoGa