Neutron studies of crystal-field effects in PrB<Subscript>6</Subscript>

The roles of various physical mechanisms in the properties of the ground state of the Pr ion in PrB₆ are studied by measuring magnetic excitation spectra in the paramagnetic and magnetically ordered phases of polycrystalline PrB₆. The ground state of the Pr ion in the paramagnetic phase is experimentally found to be triplet Γ₅. During the transition into the magnetically ordered state, this triplet splits into three singlet levels. The results obtained do not exclude the appearance of an additional contribution to the splitting induced by a decrease in the local symmetry because of structural distortions.     

Magnetic correlations in the CeAl3 heavy-fermion system

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.     

The special features of the ground state in CeAl3

The temperature (3–60 K) and transferred momentum (0.3–2.3 Å^?1) dependences of the intensity of quasi-elastic magnetic neutron scattering were studied for the polycrystalline heavy-fermion CeAl₃ compound to elucidate the special features of its ground state. Transferred momentum variations caused oscillations of the intensity of quasi-elastic magnetic neutron scattering, which was evidence of magnetic correlations in the f-electron subsystem occurring in a fairly wide temperature range.     

Dynamics of boron nanoclusters in RB12 (R = Yb,Lu) systems

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.

     

Paramagnons in the PrNi system with an induced magnetic moment

The recent studies of the PrNi system have shown that, at a temperature slightly higher than the ferromagnetic ordering temperature (T _C ～ 21 K), softening of some part of magnetic excitations occurs near the Γ point of the Brillouin zone. The magnetic modes observed have been qualitatively described by a model taking into account the crystal field and the exchang interaction within the mean-field random-phase approximation. To refine the model parameters and obtain a complete set of excitation modes, inelastic neutron scattering measurements on PrNi single crystals and polycrystals have been performed at T = 23 K. An acoustic branch related to the level with high excitation energy has been observed for the first time. The character of its dispersion suggests that the low-energy acoustic mode is responsible for the magnetic phase transition.     

Magnetic correlations in heavy fermion CeAl3 compound

To study the effect of hybridization on inter-ion correlations the measurements of the intensity of the quasielastic scattering on momentum transfer in Ce_0.9Y _0.1Al₃, Ce_0.9La_0.1Al₃ and CeAl₃ have been performed. Some hints that quasielastic magnetic scattering more sensitive to regularity in rare-earth sublattice than to the hybridization have been obtained. We also get some indications on the presence of ferromagnetic inter-ion correlations. In a contrast to quasielastic scattering the inelastic part of spectra is very sensitive to the hybridization.