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The local magnetic properties of Yb 3+ in the layered honeycomb material YbCl 3 were investigated by electron spin resonance on single crystals. For in-plane and out-of-plane field orientations the g -factor shows a clear anisotropy (g∥=2.97(8)andg⊥=1.53(4)), whereas the low temperature exchange coupling and the spin relaxation display a rather isotropic character. At elevated temperatures the contribution of the first excited crystal field level (21±2meV) dominates the spin relaxation., (Creative Commons Attribution license.)

Yb- and Ce-based delafossites were recently identified as effective spin-1/2 antiferromagnets on the triangular lattice. Several Yb-based systems, such as NaYbO 2 , NaYbS 2 , and NaYbSe 2 , exhibit no long-range order down to the lowest measured temperatures and therefore serve as putative candidates for the realization of a quantum spin liquid. However, their isostructural Ce-based counterpart KCeS 2 exhibits magnetic order below T N = 400 mK, which was so far identified only in thermodynamic measurements. Here we reveal the magnetic structure of this long-range ordered phase using magnetic neutron diffraction. We show that it represents the so-called 'stripe- yz ' type of antiferromagnetic order with spins lying approximately in the triangular-lattice planes orthogonal to the nearest-neighbor Ce-Ce bonds. No structural lattice distortions are revealed below T N , indicating that the triangular lattice of Ce 3+ ions remains geometrically perfect down to the lowest temperatures. We propose an effective Hamiltonian for KCeS 2 , based on a fit to the results of ab initio calculations, and demonstrate that its magnetic ground state matches the experimental spin structure., (Creative Commons Attribution license.)

The delafossite structure of NaYbS 2 contains a planar spin-1/2 triangular lattice of Yb 3+ ions and features a possible realisation of a quantum spin-liquid state. We investigated the Yb 3+ spin dynamics by electron spin resonance (ESR) in single-crystalline samples of NaYbS 2 . Very clear spectra with a well-resolved and large anisotropy could be observed down to the lowest accessible temperature of 2.7 K. In contrast to the ESR properties of other known spin-liquid candidate systems, the resonance seen in NaYbS 2 is accessible at low fields (<1 T) and is narrow enough for accurate characterisation of the relaxation rate as well as the g factor of the Yb 3+ spins.

The influence of external pressure on the electrical transport and magnetic properties of EuCu(2)As(2), crystallizing in a ThCr(2)Si(2)-type structure, is reported. The system is known to be an antiferromagnet below T(N) ≈ 15 K in the absence of external magnetic fields. We find that there is a gradual reduction of T(N) with the application of a magnetic field with an extrapolated value of the critical field of around 18 kOe which can drive T(N) to zero. Electrical resistivity under pressure (<11 GPa) reveals that the magnetic ordering temperature is pushed up dramatically to higher temperatures which is quite interesting if compared with the behavior in isostructural FeAs-based systems containing Eu. Above 7 GPa, the pressure-induced state appears to be ferromagnetic. The results thus reveal interesting changes in the magnetic ordering behavior of this compound with increasing pressure and magnetic fields.

The results of magnetization, heat capacity and electrical resistivity (ρ) studies of the compounds RMAs(2) (R = Pr and Sm; M = Ag, Au), crystallizing in an HfCuSi(2)-derived structure, are reported. PrAgAs(2) orders antiferromagnetically at T(N) = 5 K. The Au analog, however, does not exhibit long range magnetic order down to 1.8 K. We infer that this is due to subtle differences in their crystallographic features, particularly noting that both the Sm compounds with identical crystal structures as that of the former order magnetically nearly at the same temperature (about 17 K). It appears that, in PrAgAs(2), SmAgAs(2) and SmAuAs(2), there is an additional magnetic transition at a lower temperature, as though the similarity in the crystal structure results in similarities in magnetism as well. The ρ for PrAgAs(2) and PrAuAs(2) exhibits a negative temperature coefficient in some temperature range in the paramagnetic state. SmAuAs(2) exhibits a magnetic Brillouin-zone gap effect in ρ at T(N), while SmAgAs(2) shows a well-defined broad minimum well above T(N) around 45 K. Thus, these compounds reveal interesting magnetic and transport properties.