Thermal conductivity of $R{\mathrm{B}}_6$ ($R=\mathrm{C}\mathrm{e},\mathrm{P}\mathrm{r},\mathrm{N}\mathrm{d},\mathrm{S}\mathrm{m},\mathrm{G}\mathrm{d}$) single crystals

The thermal conductivity $\kappa$ of $R{\mathrm{B}}_6(R=\mathrm{C}\mathrm{e},\mathrm{P}\mathrm{r},\mathrm{N}\mathrm{d},\mathrm{S}\mathrm{m},\mathrm{G}\mathrm{d})$ single crystals was measured. Information on the inelastic scattering of electrons by various mechanisms for heat current was obtained, i.e., scattering by crystal-field splitting, level splitting accompanied with antiferromagnetic ordering, magnons, and short-range ordering. In Pr${\mathrm{B}}_6$, Nd${\mathrm{B}}_6$, and Ce${\mathrm{B}}_6$, in the paramagnetic region, a pronounced decrease of the Lorentz number $L$ was observed below ∼20, ∼15, and ∼25 K, respectively, which indicates an increase of the inelastic scattering. By comparing the temperature dependence on the spin-lattice relaxation rate $T_1^{-1\mathrm{}}$ in the first two compounds, it is found to be due to short-range magnetic ordering in these compounds. In Ce${\mathrm{B}}_6$, a decrease of $L$ below ∼25 K should be due to short-range quadrupole ordering, which may be related to the unusual behavior of $T_1^{-1\mathrm{}}$ and the unusual properties in the paramagnetic region in this compound. $\kappa$ of Sm${\mathrm{B}}_6$ shows a pronounced increase below ∼40 K, that is related to the gap opening in this compound.