Abstract
While the Heisenberg model for magnetic Mott insulators on planar lattice structures is comparatively well understood in the case of transition metal ions, the intrinsic spin-orbit entanglement of $4f$ magnetic ions on such lattices shows fascinating new physics largely due to corresponding strong anisotropies both in their single-ion and their exchange properties. We show here that the Yb delafossites, containing perfect magnetic ${\mathrm{Yb}}^{3+}$ triangular lattice planes with pseudospin $s=\frac{1}{2}$ at low temperatures, are an ideal platform to study these phenomena. Competing frustrated interactions may lead to an absence of magnetic order associated to a gapless spin liquid ground state with a huge linear specific heat exceeding that of many heavy fermions, whereas the application of a magnetic field induces anisotropic magnetic order with successive transitions into different long-range ordered structures. In this comparative study, we discuss our experimental findings in terms of a unified crystal-field and exchange model. We combine electron paramagnetic resonance (EPR) experiments and results from neutron scattering with measurements of the magnetic susceptibility, isothermal magnetization up to full polarization, and specific heat to determine the relevant model parameters. The impact of the crystal field is discussed as well as the symmetry-compatible form of the exchange tensor, and we give explicit expressions for the anisotropic $g$ factor, the temperature dependence of the susceptibility, the exchange-narrowed EPR linewidth, and the saturation field.
Highlights
We would like to discuss our findings and review further available results about an interesting class of compounds— Ytterbium Yb3+ delafossites
The importance of the 4f ions comes into play: Among them, the Kramers ions with an odd number of electrons or holes in the 4f shelllike Ce3+ or Yb3+ have a pronounced doublet ground state due to a low-symmetry crystal electric field (CEF)
Ground state of the Yb3+ ion Lowering the local symmetry of the crystal field from cubic to trigonal by compressing the threefold axis parallel to the c direction splits the 8 quartet obtained so far into two Kramers doublets and all six crystal field parameters in Eq (1) become independent
Summary
We would like to discuss our findings and review further available results about an interesting class of compounds— Ytterbium Yb3+ delafossites. The importance of the 4f ions comes into play: Among them, the Kramers ions with an odd number of electrons or holes in the 4f shelllike Ce3+ or Yb3+ have a pronounced doublet ground state due to a low-symmetry crystal electric field (CEF) In this respect, we underscore that Yb delafossites are ideal model systems for the study of spin-. The corresponding wave functions of HC(cEuFbic,3) which are grouped in Kramers pairs consisting of time-reversed states are given by They are independent of the crystal-field parameters and determined by symmetry only. C. Ground state of the Yb3+ ion Lowering the local symmetry of the crystal field from cubic to trigonal by compressing the threefold axis parallel to the c direction splits the 8 quartet obtained so far into two Kramers doublets and all six crystal field parameters in Eq (1) become independent.
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