M. Klicpera

The development of specific heat and electrical resistivity in the CeNixPd1−xIn series

Our report describes the anomalous electronic behavior of CeNi(x)Pd(1-x)In compounds studied by specific heat and electrical resistivity measurements. These compounds belong to the large and relatively thoroughly studied group of ternary rare-earth intermetallics crystallizing in the ZrNiAl-type structure. The investigated series shows a transition from the heavy fermion antiferromagnetic system of CePdIn to the valence fluctuating state observed in CeNiIn. The isostructural and isoelectronic substitution of Pd by Ni leads to a change in the character of the d-electrons and the lattice parameters of the system because of the smaller radius of Ni atoms. These changes have a great impact on the magnetic properties of the studied compounds. The antiferromagnetic transition shifts first to lower temperatures, from T(N) = 1.7 K for CePdIn to T(N) = 1.3 K for CeNi0.2Pd0.8In. For a Ni content ≥40%, there is no sign of a magnetic phase transition in the specific heat and electrical resistivity data. Moreover, the data indicate anomalous non-Fermi-liquid behavior for concentrations with 0.4 ≤ x ≤ 0.6, which is clearly seen in both types of measurements. The rest of series behaves similarly to the second parent compound CeNiIn. Besides the cerium compounds, superconductivity in LaNi0.2Pd0.8In is also presented.

Magnetic structures of non-cerium analogues of heavy-fermion Ce

R2RhIn8 compounds (space group P4/mmm, R is a rare-earth element) belong to a large group of structurally related tetragonal materials which involves several heavy-fermion superconductors based on Ce. We have succeeded to grow single crystals of compounds with Nd, Dy and Er and following our previous bulk measurements, we performed neutron-diffraction studies to determine their magnetic structures. The Laue diffraction experiment showed that the antiferromagnetic order below the Neel temperature is in all three compounds characterized by the propagation vector k = (1/2, 1/2, 1/2). The amplitude and direction of the magnetic moments, as well as the invariance symmetry of the magnetic structure, were determined by subsequent experiments using two- and four-circle diffractometers. The critical exponents were determined from the temperature dependence of the intensities below TN.

_2

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.

RhIn

Volume 26 • Number 3 • 2015 Neutron News 18 Introduction Electronic many-body systems in crystalline materials partly reveal their enigmatic behavior via their magnetic fi ngerprints, which can be formalized in the generalized magnetic susceptibility χ(Q,ω). The neutron is a probe that provides a weak magnetic perturbation into these systems and the linear response, expressed by the imaginary part of the magnetic susceptibility, can be directly related to the scattering function of the neutron via the fl uctuation dissipation theorem [1]. No other magnetic probe provides such detailed information on space and time correlations in magnetic systems as single crystal neutron spectroscopy. Over decades the two cold three-axis spectrometers at the ILL, IN14 and IN12 (CRG of FZ Jülich and CEA Grenoble), contributed to discover and unravel magnetic correlations in classical and non-conventional superconductors, multiferroic crystals and a in wide variety of low-dimensional, frustrated and quantum magnetic systems. Both instruments dated from 1980s and needed a complete refurbishment to be able to contribute to the scientifi c progress in those fi elds. The relocation and refurbishment of the new IN12 [2] has been fi nished in 2012. By the end of 2014 the IN14 spectrometer has been replaced by its successor ThALES [3–5]. The major goals of the ThALES project have been threefold:

_8

Magnetic structure of tetragonal UAu

: The case of Nd

_2

_2

Si

RhIn

_2

_8

was investigated by single-crystal neutron diffraction experiments. Below

, Dy

T_{\rm N}