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We show, with the help of polarized neutrons, that the cubic magnets Fe1-xCoxSi with Dzyaloshinskii-Moriya interaction can be switched between left (for x=0.1, 0.15) and right (for x=0.2, 0.25, 0.3, 0.5) chiral states of the spin helix. The absolute structure was evaluated using x-ray diffraction. The crystals are shown to be enantiopure and the structural chirality changes from right handed for x<0.2 to left handed for x>0.2. These compounds are compared with the etalon sample of MnSi which is identified as having the left-handed chirality both in the magnetic and crystallographic sense.

The near normal incidence reflectivity of UO2 single crystals has been measured in the photon energy range from 0.03 eV to 13 eV. From the reflectivity spectrum the complex dielectric function ε (ω) =ε1(ω)+iε2(ω) has been derived by means of the Kramers-Kronig relation. In addition the absorption coefficient was determined from a direct transmission measurement on thin single crystal plates in the weakly absorbing spectral region below the absorption edge. An energy level scheme is proposed which allows a self-consistent assignment of the structure in ε2 with optical transitions between maxima in the density of states. The energy gap found at 2.1±0.1 eV is attributed to a 5f2→5f16deg transition. A crystal field splitting 10Dq=2.8 eV is derived for the 6d conduction states. Good agreement is obtained within this model with XPS measurements and a recent molecular cluster approximation. It disagrees with a previous interpretation of reflectivity data.

Hall-effect and resistivity study of the heavy-fermion system Uru2si2 Schoenes, J.; Schönenberger, C.; Franse, J.J.M.; Menovsky, A.A.

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A comparison of high-resolution, angle-resolved photoemission spectroscopy (ARPES) data with ab initio band-structure calculations by density functional theory for the anticipated Kondo insulator FeSi shows that the experimental dispersions can quantitatively be described by an itinerant behavior provided that an appropriate self-energy correction is included, whose real part describes the band renormalization due to interactions of the Fe 3d electrons. The imaginary part of the self-energy, on the other hand, determines the linewidth of the quasiparticle peaks in the ARPES data. We use a model self-energy which consistently describes both the renormalized single-particle dispersion and the energy-dependent linewidth of the Fe 3d bands. These results are clear evidence that FeSi is an itinerant semiconductor whose properties can be explained without a local Kondo-like interaction.

Because of its apparent simplicity, diffusion of hydrogen in solids can be regarded as a general model system for diffusion. However, only rudimentary knowledge exists for the dynamics of hydrogen in complex hydrides. Insight into the specific diffusion process is given by hydrogen-deuterium exchange experiments. Thermogravimetry and Raman spectroscopy are used to measure the hydrogen-deuterium exchange during the decomposition of LiBH4. At a temperature of 523 K the self-diffusion constant of deuterium in LiBH4 is estimated to be D approximately 7 x 10(-14) m(2) s(-1). A careful analysis of the Raman spectra shows that hydrogen is statistically exchanged by deuterium in LiBH4; i.e., the diffusing species is assumed to be the single hydrogen atom.