The crystalline electric field (CEF) level scheme and magnetic structure of a tetragonal antiferromagnet CePd
Al
with Formula: see text K and Formula: see text K were studied by neutron scattering, ...magnetization and magnetoresistance measurements. Inelastic neutron scattering measurements on the powder sample revealed CEF excitations at 21.3 and 22.4 meV. The derived wave functions of the CEF ground state for the Ce
ion consist primarily of Formula: see text under the tetragonal symmetry. By means of single-crystal neutron diffraction, magnetic Bragg peaks characterized by a propagation vector Formula: see text were observed at Formula: see text. Our analysis indicates a sinusoidally modulated magnetic structure with amplitude of 2.0(1) Formula: see text/Ce, where the magnetic moments point to the Formula: see text-axis. The intensity of the third-order harmonic at 0.8 K is 1/30 as small as that expected for an antiphase structure, suggesting that the modulated structure remains at least down to 0.8 K. Both the magnetization and magnetoresistance show several anomalies in the magnetically ordered phase, indicating field-induced successive changes of the magnetic structure.
CeCuAl
crystallizing in the tetragonal BaNiSn
-type structure and CeCu
Al
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 + δ
, 0.60 + δ
, 0), where δ
≈ 0.02 and δ
≈ 0.01. The magnetic structure of CeCu
Al
consists of two components: an anti-ferromagnetic one described by the same k and a ferromagnetic one with k
= (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 CeCu
Al
was studied by inelastic neutron scattering. The measured spectra of CeCuAl
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 CeCu
Al
system and the coupling between the lattice vibrations and the crystal electric field excitations.
The recent discovery of topological Kondo insulating behaviour in strongly correlated electron systems has generated considerable interest in Kondo insulators both experimentally and theoretically. ...The Kondo semiconductors CeT2Al10 (T=Fe, Ru and Os) possessing a c-f hybridization gap have received considerable attention recently because of the unexpected high magnetic ordering temperature of CeRu2Al10 (TN=27 K) and CeOs2Al10 (TN=28.5 K) and the Kondo insulating behaviour observed in the valence fluctuating compound CeFe2Al10 with a paramagnetic ground state down to 50 mK. We are investigating this family of compounds, both in polycrystalline and single crystal form, using inelastic neutron scattering to understand the role of anisotropic c-f hybridization on the spin gap formation as well as on their magnetic properties. We have observed a clear sign of a spin gap in all three compounds from our polycrystalline study as well as the existence of a spin gap above the magnetic ordering temperature in T=Ru and Os. Our inelastic neutron scattering studies on single crystals of CeRu2Al10 and CeOs2Al10 revealed dispersive gapped spin wave excitations below TN. Analysis of the spin wave spectrum reveals the presence of strong anisotropic exchange, along the c-axis (or z-axis) stronger than in the ab-plane. These anisotropic exchange interactions force the magnetic moment to align along the c-axis, competing with the single ion crystal field anisotropy, which prefers moments along the a-axis. In the paramagnetic state (below 50 K) of the Kondo insulator CeFe2Al10, we have also observed dispersive gapped magnetic excitations which transform into quasi-elastic scattering on heating to 100 K. We will discuss the origin of the anisotropic hybridization gap in CeFe2Al10 based on theoretical models of heavy-fermion semiconductors.
We report the results of a muon-spin rotation (μSR) experiment to determine the superconducting ground state of the iron-based superconductor CsCa2Fe4As4F2 with Tc≈28.3K. This compound is related to ...the fully gapped superconductor CaCsFe4As4, but here the Ca-containing spacer layer is replaced with one containing Ca2F2. The temperature evolution of the penetration depth strongly suggests the presence of line nodes and is best modeled by a system consisting of both an s- and a d-wave gap. We also find a potentially magnetic phase which appears below ≈10K but does not appear to compete with the superconductivity. This compound contains the largest alkali atom in this family of superconductors, and our results yield a value for the in-plane penetration depth of λab(T=0)=244(3)nm.
Identifying the symmetry of the wave function describing the Cooper pairs is pivotal in understanding the origin of high-temperature superconductivity in iron-based superconductors. Despite nearly a ...decade of intense investigation, the answer to this question remains elusive. Here, we use the muon spin rotation/relaxation (μSR) technique to investigate the underlying symmetry of the pairing state of the FeSe superconductor, the basic building block of all iron-chalcogenide superconductors. Contrary to earlier μSR studies on powders and crystals, we show that while the superconducting gap is most probably anisotropic but nodeless along the crystallographic c axis, it is nodal in the ab plane, as indicated by the linear increase of the superfluid density at low temperature. We further show that the superconducting properties of FeSe display a less pronounced anisotropy than expected.
We have investigated the local low-energy excitations in CeRu4Sn6, a material discussed recently in the framework of strongly correlated Weyl semimetals, by means of Ce M5 resonant inelastic x-ray ...scattering (RIXS). The availability of both F522 and F722 excitations of the Ce 4f1 configuration in the spectra allows for the determination of the crystal-electric field (CEF) parameters that explain quantitatively the high-temperature anisotropy of the magnetic susceptibility. The absence of an azimuthal dependence in the spectra indicates that all CEF states are close to being rotational symmetric. We show further that the non-negligible impact of the Ǎ60 parameter on the ground state of CeRu4Sn6 leads to a reduction of the magnetic moment μc due to multiplet intermixing. This improves the agreement between CEF calculations and the experimentally determined magnetic susceptibility considerably at low temperatures. Deviations that persist at low temperatures for fields within the tetragonal plane are attributed to the Kondo interaction between 4f and conduction electrons. The RIXS results are consistent with inelastic neutron scattering data and are compared to the predictions from ab initio based electronic structure calculations.
PDF
