[en] Recent magneto-optical investigations of exotic rare-earth compounds, such as reduced-moment magnets and magnetic superconductors, are critically reviewed. Representatives of the first class are cerium compounds like CeSb and CeRh₃B₂. The former material has attracted particular theoretical attention due to its record Kerr rotation of 14 . CeRh₃B₂ raised the question, whether a Curie temperature of 115 K can originate from reduced Ce moments. A line shape analysis of the magneto-optical spectra shows that Ce, indeed, is responsible for the moment in CeRh₃B₂ and it allows to specify the nature of its ground state. Representatives of the second class are Chevrel phases containing Eu²⁺ ions. The characteristic magneto-optical spectrum of this ion has been identified in various Eu_1-xPb_xMo₆S₈ and Eu_1-xSn_xMo₆S_8-ySe_y Chevrel phases. The temperature and field dependence of the Kerr rotation allow a study of the evolution of the spin polarization of the 4f⁷ state in the normal, superconducting and field-induced superconducting state. (orig.)

[en] The absorption coefficient and the interband Faraday rotation of EuS, EuSe and EuTe thin films have been measured as function of the photon energy (1-6 eV), the temperature (2.7-300 K) and the applied magnetic field (0-11.5 kOe). In addition a magnetic field modulation technique has been developed, with a resolution of 2 x 10^-4 deg. This allows the measurement of the Faraday rotation in fields of only 100 Oe, which is important for metamagnetic samples with low critical fields. (orig./HPoe)

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[en] A low-temperature electron diffraction study has been carried out on ThAsSe to search for evidence of structural disorder associated with the low-temperature non-magnetic Kondo effect. A highly structured and extremely complex characteristic diffuse intensity distribution has been observed at low temperature and interpreted in terms of a gradual charge density wave type phase transition upon lowering of temperature involving disordered As-As dimerization within (001) planes. Plausible models of the proposed As-As dimerization have been obtained using a group theoretical approach

[en] Optical reflectivity measurements on CePd³ and ThPd³ have been performed for photon energies from 0.03 to 12 eV. A strong similarity between the Kramers-Kronig derived optical conductivity and X-ray photoelectron spectra is observed. The 4f binding energy in CePd³ is derived to be <0.3 eV. (Auth.)

[en] 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 epsilon (ω) =epsilon₁(ω)+iepsilon₂(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 epsilon₂ 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→5f¹6de/sub g/ 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

No abstract available

No abstract available

[en] Systematic absorption measurements on UO₂ single crystals are reported. The temperature dependence of the absorption edge above 2 eV gives strong evidence for a 5f²→5f¹6desub(g) transition. Numerous absorption lines are observed below 2 eV which can be assigned to intra-5f transitions. The first excited level GAMMA₃ is found 0.23 eV above the ground state GAMMA₅. (Auth.)

[en] Single crystals of the uranium chalcogenides US. USe. UTe and the pnictides UAs and USb have been cleaved under high and altrahigh vacuum conditions and the near normal incidence reflectivity has been measured in situ from 0.03 to 12 eV. In the case of US the spectral range of the measurement was further extended down to 0.0017 eV. The various optical functions (epsilon₁, epsilon₂, sigma, E sub(l)sub(o)sub(s)sub(s), nsub(e)sub(f)sub(f)) have been deduced by a Kramers-Kronig analysis. Typical features of all spectra are weak intraband contributions and the extension of strong interband transitions to very low photon energies. Highly damped plasmons are found at 4.25 eV for USe and 2.2 eV for UTe. For the pnictides UAs and USb the corresponding values are 2 eV and 1.6 eV. respectively. The apparent contradiction between the presence of a large number of conduction electrons and only very weak intraband contributions is resolved within the spectral exclusion model of Keller. In this self-consistent cellular multiple scattering calculation the coupling of the narrow 5f states and the much wider 6d states produces a dip in the density of d states near Esub(F) where the f electrons form a resonance state. Quantitative agreement is obtained between theory and experiment for US. For all investigated compounds empirical energy level schemes are derived. The reflectivity measurements down to 1.7 MeV for US reveal the existence of a further excitation at 39 MeV which is assigned to a transverse optical phonon mode. This unique observation of an optical phonon in a direct reflectivity measurement of a metal supports the picture of a small density of conduction electrons at Esub(F). Further arguments in favor of the spectral exclusion model are presented and the question of the localization of the 5f electrons in various ceranium compounds is discussed. (orig.)