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The magnetic properties of the lanthanide chalcogenides are much less explored than the monopnictides. The main reasons are probably difficulties in syntheses and the crystals growth. In particular, the properties of monotellurides are almost completely unknown. The dysprosium tellurides: DyTe and Dy2Τe3, crystallize in the structures related to the rock salt type. The first compound is metallic, while the second — semiconducting. Dysprosium sesquitelluride behaves like a simple antiferromagnet with the Neel temperature equal to 4.1 K [1]. We synthesized and investigated the dysprosium monnotelluride in order to examine a change of exchange interactions after transition to the metallic state.

FeSc2S4, MnSc2S4 and MnSc2Se4 crystallize in the normal spinel structure. None of them orders magnetically above 4.2 K contrary to FeLu2S4, which orders at 8 K. This difference is discussed as being strongly dependent on the transfer of divalent iron to the octahedral sites and not on the interionic distances.

The specific heat and electrical resistivity results are presented for UCu 4.5 Al 7.5 , a magnetically ordered nearly heavy fermion compound. The specific heat data do not indicate the expected anomaly characteristic for the magnetic order transition; only a very weak one was detected, which has been separated using a simple theoretical procedure. The electronic specific heat coefficient has been estimated to be 118 mJ mol −1 K −2 . The other heavy fermion coefficients have also been calculated. The electrical resistivity data for UCu 4.5 Al 7.5 include indications of strong crystal field effects.

Elastic and inelastic neutron scattering studies of the Kondo lattice CeCu2Ge2 were performed. AtTN=4.1 K an incommensurate magnetic order develops with an ordering wave vectorq0=(0.28, 0.28, 0.54) and an ordered moment µs=0.74 µB. The crystalline electric field splits the 4f1-J-multiplet of the Ce ion into a ground state doublet and a quartet at 191 K. The wave function of the ground state yields an ordered moment of 1.54µB. Thus, due to the onset of the formation of a Kondo singlet the magnetic moment is considerably reduced. The magnetic relaxation rate Λ was investigated via quasielastic neutron scattering. The temperature dependence of Λ(T) is characteristic of heavy-fermion systems with a high temperature square root dependence and a limiting low temperature value, yielding a Kondo temperatureTK≈10K. The quasielastic component of the scattered neutron intensities persists down to the lowest temperatures, well belowTN. This quasielastic line is regarded as a characteristic feature of heavy-fermion systems and corresponds to the enhanced value of the linear term of the specific heat.

Magnetic, calorimetric and transport measurements characterize CeCu2Ge2 as a Kondo–lattice system which orders antiferromagnetically below TN = (4.15 ± 0.05) K. The low-temperature specific heat shows a magnon-derived T3 term and, in addition, an electronic contribution γ(T)T. γ(T) extrapolates to 0.1 J/K2mol as T → 0 and assumes a large maximum of 0.22 J/K2mol at T = 0.45 K.

CdB2X4 spinels—B = Sc, Y, Lu; X = S, Se—were synthesized and their lattice constants were determined. After Mn2+ doping they were investigated by the EPR method over the temperature range 4.2–330 K. The temperature dependence of the hyperfine structure constant, A, was described by the Simanek-Orbach equation and its parameters were determined. Chemical bonds in the studied spinels were characterized in more detail to obtain a linear dependence of the A constants on the modified covalency parameter.

The paramagnetic susceptibility of polycrystalline CdYb2Se4 spinel has been measured between 4 and 300 K. The data are interpreted within the crystal field approximation and a correction is made taking into account exchange interactions. The energy levels and crystal field parameters b4 and b6 have been calculated. La susceptibilitye paramagnetique d'un echantillon polycristallin de CdYb2Se4 de structure spinelle a ete mesuree entre 4 et 300 K. Elle est interpretee avec une approximation du champ cristallin et corrighe d'un terme dǔ aux interactions d'ehchange. On a calcule les niveaux d'energie et les parametres de champ cristallin: b4 et b6.

Magnetic susceptibility of the polycrystalline ζ-Yb2Se3 has been measured within the temperature range 4.2–300 K. From the χ(T) dependence crystal field splitting of the ground term 2 F 7 2 has been estimated: E(Γ6) = 0, E(Γ8) = 155 and E(Γ7) = 350 cm−1. It allowed to calculate the crystal field parameters b4 = −25.1 and b6 = 0.72 cm−1. The agreement between the experimental and calculated results was improved by taking into account the orbital reduction factor k = 0.96.

Results of the susceptibility, specific heat and thermal expansion are reported for the compounds CeM 2 Ge 2 (M: Ag, Au, Ru), which order antiferromagnetically below T N = 5 K (Ag) and 15 K (Au) and ferromagnetically below T c = 7.5 K (Ru). Distinct maxima in the electronic specific heat coefficient γ( T ) at 0.3 K for the Ag- and Au-based compounds hint at a coexistence of coherent electronic quasiparticles of “medium”-heavy mass with magnetic order.

The magnetic properties of the heavier lanthanide sesquiselenides were studied as early as 1937 by Klemm and Koczy 1 and later in the 1970’s by a group of Soviet investigators2,3. The measurements were carried out down to liquid nitrogen temperature, and they gave linear plots of the temperature dependence of the reciprocal magnetic susceptibility. The widening of the measurement range down to helium temperatures makes a more detailed interpretation of magnetic properties possible, relating magnetic susceptibility to crystal field effects. Such an analysis becomes simplest in the case of compounds with a high symmetry of the magnetic ion environment. This is the reason for our interest in sesquiselenides with the Sc2S3 crystal structure, since they are the ones which demonstrate an octahedral environment of metal ions. The orthorhombic Sc2S3 structure arises from the NaCl structure by removing 1/3 of the cations in an ordered manner. The first coordination sphere of each metal ion contains six selenide ions forming a slightly distorted octahedron. The deviations of the lattice constant ratios a/b and c/b from their ideal values, being equal to $\sqrt{2}$ and 3 respectively, can be taken as a measure of that distortion.

Crystal field parameters of Ce 3+ in tetragonal TlCeSe 2 and TlCeTe 2 were determined from the magnetic susceptibility measurements down to 4.2 K: B 0 2 = -14.7 K and -6.9 K, B 0 4 = -0.38 K and -0.39 K, B 4 4 = 3.8 K and 9.8 K for selenide and telluride, respectively.

The magnetic susceptibility and the high field magnetization of MgYb 2 S 4 and MgYb 2 Se 4 have been measured. A weakly deformed octahedral crystal field was found with x = -0.959, W = 22.4 K, B 0 2 = -0.30 K for the sulphide and x = -0.977, W = 22.6 K, B 0 2 = -0.082 K for the selenide.