We have investigated the noncentrosymmetric tetragonal heavy-fermion antiferromagnetic compound CeCuAl3 (T(N)=2.5 K) using inelastic neutron scattering (INS). Our INS results unequivocally reveal the presence of three magnetic excitations centered at 1.3, 9.8, and 20.5 meV. These spectral features cannot be explained within the framework of crystal-electric-field models and recourse to Kramers' theorem for a 4f(1) Ce(3+) ion. To overcome these interpretational difficulties, we have generalized the vibron model of Thalmeier and Fulde for cubic CeAl(2) to tetragonal point-group symmetry with the theoretically calculated vibron form-factor. This extension provides a satisfactory explanation for the position and intensity of the three observed magnetic excitations in CeCuAl3, as well as their dependence on momentum transfer and temperature. On the basis of our analysis, we attribute the observed series of magnetic excitations to the existence of a vibron quasibound state.

No abstract

We have investigated the noncentrosymmetric tetragonal heavy fermion compound CeAuAl 3 using muon spin rotation (μSR), neutron diffraction (ND), and inelastic neutron scattering (INS) measurements. We have also revisited the magnetic, transport, and thermal properties. The magnetic susceptibility reveals an antiferromagnetic transition at 1.1 K with, possibly, another magnetic transition near 0.18 K. The heat capacity shows a sharp λ-type anomaly at 1.1 K in zero field, which broadens and moves to a higher temperature in an applied magnetic field. Our zero-field μSR and ND measurements confirm the existence of a long-range magnetic ground state below 1.2 K. Further, the ND study reveals an incommensurate magnetic order with a magnetic propagation vector k = (0,0,0.52(1)) and a spiral structure of Ce moments coupled ferromagnetically within the ab plane. Our INS study reveals the presence of two well-defined crystal electric field (CEF) excitations at 5.1 and 24.6 meV in the paramagnetic phase of CeAuAl 3 that can be explained on the basis of the CEF theory and the Kramer's theorem for a Ce ion having a 4f 1 electronic state. Furthermore, low energy quasielastic excitations show a Gaussian line shape below 30 K compared to a Lorentzian line shape above 30 K, indicating a slowdown of spin fluctuations below 30 K. We have estimated a Kondo temperature of T K = 3.5 K from the quasielastic linewidth, which is in good agreement with that estimated from the heat capacity. This study also indicates the absence of any CEF-phonon coupling unlike that observed in isostructural CeCuAl 3 The CEF parameters, energy level scheme, and their wave functions obtained from the analysis of INS data explain satisfactorily the single crystal susceptibility in the presence of two-ion anisotropic exchange interaction in CeAuAl 3 .

We report the magnetic and transport properties of a new ternary intermetallic compound, CeRhSn₃, using magnetic susceptibility, magnetization, specific heat, electrical resistivity, muon-spin relaxation (μSR) and neutron diffraction investigations. The dc magnetic susceptibility data reveal two magnetic phase transitions at 0.9 and 4 K. The overall behavior of dc susceptibility and magnetization indicates a ferrimagnetic-type phase transition near 4 K. The specific heat data also exhibit sharp λ-type anomalies at 1 and 4 K. The behavior of the specific heat anomaly under the application of a magnetic field suggests that the 1 K transition is probably related to a transition from a ferri- to a ferromagnetic state. The low temperature specific heat exhibits an enhanced Sommerfeld coefficient γ (~100 mJ mol⁻¹ K⁻²) due to the formation of a moderate heavy fermion state. The resistivity of CeRhSn₃ demonstrates an interplay between the RKKY and Kondo interactions which is further modified by the presence of the crystal electric field. Interestingly, the resistivity of the nonmagnetic reference compound, LaRhSn₃, is found to increase with decreasing temperature. Further, the onset of long-range magnetic order below 1 K is confirmed from our μSR study on CeRhSn₃. However, the 4 K transition is not detected in the μSR and low temperature neutron diffraction data. Analysis of the dc magnetic susceptibility data within the framework of a two-sublattice model of ferrimagnetism supports the ferrimagnetic-type transition at 4 K in CeRhSn₃. We have observed an unusual frequency dependence of the peak near 4 K in the ac susceptibility, which shows that the transition temperature shifts toward the lower temperature side with increasing frequency.

The temperature dependence of the dynamic structure factor at next-neighbour distances has been investigated for liquid aluminium. This correlation function is a sensitive parameter for changes in the local environment and its Fourier transform was measured in a coherent inelastic neutron scattering experiment. The zero frequency amplitude decreases in a nonlinear way and indicates a change in dynamics around 1.4 ∙ Tmelting. From that amplitude a generalized viscosity can be derived which is a measure of local stress correlations on next-neighbour distances. The derived generalized longitudinal viscosity shows a changing slope at the same temperature range. At this temperature the freezing out of degrees of freedom for structural relaxation upon cooling sets in which can be understood as a precursor towards the solid state. That crossover in dynamics of liquid aluminium shows the same signatures as previously observed in liquid rubidium and lead, indicating an universal character.

No abstract

No abstract

No abstract