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The density of phonon states for the YbB12 Kondo insulator is calculated from the inelastic neutron scattering spectra of this compound. It is established that thermal vibrations of rare-earth atoms predominantly occur in the low-energy range. These atoms are most weakly bound in the crystal structure of the YbB12 Kondo insulator. The high-energy part of the vibrational spectrum is determined by thermal vibrations of the boron atoms forming a rigidly connected structure of the compound. It is revealed that the temperature dependence of the intensity of the phonon peak attributed to thermal vibrations of the ytterbium atoms exhibits an anomalous behavior. This circumstance suggests that the magnetoelastic coupling occurring in the structure of the YbB12 Kondo insulator is relatively strong and can contribute to the magnetic excitation spectrum of this compound. [ABSTRACT FROM AUTHOR]

The results of investigations into the spin dynamics in the YbB12 Kondo insulator with the use of inelastic neutron scattering, including experiments with a polarization analysis, are discussed. It is shown that, at low temperatures, the dynamic magnetic response in the structure of the YbB12 Kondo insulator is characterized by three dispersive excitations with a nontrivial q-dependence of the intensity. An increase in the temperature results in a crossover to the single-site spin fluctuation regime accompanied by suppression of collective excitations. [ABSTRACT FROM AUTHOR]

The results obtained from experiments on inelastic neutron scattering in the YbB12 Kondo insulator are discussed. The structure of the magnetic excitation spectra and their evolution under variations in temperature are interpreted in the framework of a simple phenomenological model with due regard for the crystal field effects renormalized as a result of the influence of the intermediate valence state. [ABSTRACT FROM AUTHOR]

The inelastic neutron scattering spectra of the CeAl3 heavy-fermion system are measured over a wide range of momentum transfers with the aim of determining the type of ion-ion magnetic correlations. The oscillatory dependence of the intensity of quasi-elastic magnetic neutron scattering on the momentum transfer is revealed at temperatures lower than those corresponding to the energy of splitting in the crystal electric field. An analysis of the obtained dependence of the intensity of quasi-elastic magnetic neutron scattering indicates the presence of short-range ferromagnetic correlations in the system. [ABSTRACT FROM AUTHOR]

The phonon dispersion in RB12 ( R = Yb, Lu) systems is studied in detail using inelastic neutron scattering over a wide range of energies (up to 55 meV). It is demonstrated that the main features of the lattice dynamics in the RB12 crystals can be described in terms of a simple model of force constants with a strong hierarchy of interatomic interactions in the systems: B-B ≫ B- R ≫ R- R. An interesting feature of the low-energy portion of the phonon spectrum is the weakly dispersive optical mode. According to the model calculations, this mode is associated with the relative displacements and “breathing” vibrations of the boron nanoclusters B12. [ABSTRACT FROM AUTHOR]