Lattice dynamics in CePd2Al2 and LaPd2Al2.

The interaction between phonons and 4f electrons, which is forming a new quantum state (quasi-bound state) beyond Born-Oppenheimer approximation, is very prominent and lattice dynamics plays here a key role. There is only a small number of compounds in which the experimental observation suggest such a scenario. One of these compounds is CePd2Al2. Here the study of phonon dispersion curves of (Ce,La)Pd2Al2 at 1.5, 7.5, 80 and 300 K is presented. The inelastic X-ray scattering technique was used for mapping the phonon modes at X and Z points as well as in Λ and Δ directions, where the symmetry analysis of phonon modes was performed. The measured spectra are compared with the theoretical calculation, showing very good agreement. The measurements were performed in several Brillouin zones allowing the reconstruction of phonon dispersion curves. The results are discussed with respect to the magneto-elastic interaction and are compared with other cerium compounds. The phonon mode symmetry A1g was found to be unaffected by the interaction, which is in contrast to previous assumptions.

CePt2Al2: Structural and Bulk Properties.

This work is focused on the structural and physical properties of CePt2Al2, an intermetallic compound. At room temperature, the modulated orthorhombic structure Cmme(a00)000, with q→= (0.481, 0, 0) has been determined by single-crystal X-ray diffraction supplemented by dependence of lattice parameters above room temperature for which the X-ray powder diffraction was used. The compound undergoes a structural transition to a tetragonal structure above room temperature. This transition exhibits 50 °C hysteresis and creates a domain structure in the sample. The magnetic behavior has been studied by specific heat, magnetization, and transport measurements in the temperature range between 0.5 and 300 K. Specific heat and susceptibility shows an antiferromagnetic order below 2 K. On the basis of electrical resistivity and other bulk measurements, CePt2Al2 can be considered a Kondo lattice material. The presence of a modulated crystal structure opens the possibility of a charge density wave state in CePt2Al2 as observed for (Re)Pt2Si2.

Local atomic arrangement in LaCuAl3 and LaAuAl3 by NMR and density functional theory.

CeCuAl3 and CeAuAl3, crystallizing in the non-centrosymmetric BaNiSn3 tetragonal structure, are known mainly for their unusual neutron scattering spectra involving additional excitations ascribed to vibron quasi-bound quantum state in CeCuAl3 and anti-crossing of phonon and crystal field excitations in CeAuAl3. In this work, we present results of nuclear magnetic resonance (NMR) experiments on their lanthanum analogues-[Formula: see text] and [Formula: see text]. The character of NMR spectra of [Formula: see text], [Formula: see text], and 65Cu measured in [Formula: see text] and [Formula: see text] is dominated by electric quadrupole interaction. The spectral parameters acquired from experimental data are confronted with values obtained from the electronic structure calculations. The results show remarkable differences for the two compounds. The [Formula: see text] spectrum in [Formula: see text] can be interpreted by a single spectral component corresponding to uniform environment of La atoms in the crystal structure, whereas for [Formula: see text] the spectrum decomposition yields a wide distribution of spectral parameters, which is not possible to explain by a single La environment, and multiple non-equivalent La positions in the crystal structure are required to interpret the spectrum.

Crystal field in NdPd5Al2 investigated by inelastic neutron scattering.

We report on inelastic neutron scattering measurements of the antiferromagnetic NdPd5Al2 compound. NdPd5Al2 crystallizes in the tetragonal I4/mmm space group and exhibits a distinct uniaxial anisotropy due to crystal field effects. In this study, we have revealed the crystal field energy levels of NdPd5Al2 composed of five Kramers doublets. The corresponding four inelastic excitations are located at energies 3.0 meV, 7.4 meV, 8.6 meV and 17.1 meV. We additionally interpreted the neutron spectra within a crystal field model. It has been established that the crystal field parameters found by a Monte Carlo technique and the derived ground-state wavefunctions consisting primarily of the [Formula: see text] states reproduce correctly magnetic susceptibility data.

Magnetic Structure and Excitations in CeCuxAl4-x System.

CeCuAl3 crystallizing in the tetragonal BaNiSn3-type structure and CeCuxAl4-x solid solutions were investigated by means of elastic and inelastic neutron scattering. Powder neutron diffraction brought information on both temperature evolution of crystallographic parameters and magnetic order at low temperatures. No structural change was observed in the investigated temperature range from 1.5 to 300 K. Weak magnetic peaks outside nuclear Bragg positions observed in solid solutions with 0.90 ≤ x ≤ 1.10 were described by the propagation vector k = (0.40 + δx, 0.60 + δy, 0), where δx ≈ 0.02 and δy ≈ 0.01. The magnetic structure of CeCu0.75Al3.25 consists of two components: an anti-ferromagnetic one described by the same k and a ferromagnetic one with k0 = (0, 0, 0) and magnetic moments lying within the tetragonal basal plane. The evolution of magnetic excitations as a function of Cu-Al concentration in CeCuxAl4-x was studied by inelastic neutron scattering. The measured spectra of CeCuAl3 and the solution with x = 0.95 point to a three-magnetic-peak energy scheme, while only two excitations are expected from the local symmetry conditions on Ce atoms. The standard two-peak spectrum of crystal electric field excitations was observed for Cu-Al substitutions further from the 1:1:3 stoichiometry (x = 0.75 and 1.10). The intermediate concentrations (x = 0.90 and 1.05) exhibit spectra on the border between the former cases with a less clear pronounced first inelastic magnetic peak. The observed behavior is discussed considering the evolution of structural parameters in the CeCuxAl4-x system and the coupling between the lattice vibrations and the crystal electric field excitations.