Thermal conductivity of RB6 (R=Ce,Pr,Nd,Sm,Gd) single crystals

The thermal conductivity κ of RB₆(R=Ce,Pr,Nd,Sm,Gd) 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 PrB₆, NdB₆, and CeB₆, 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^-1₁ in the first two compounds, it is found to be due to short-range magnetic ordering in these compounds. In CeB₆, 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^-1₁ and the unusual properties in the paramagnetic region in this compound. κ of SmB₆ shows a pronounced increase below ~40 K, that is related to the gap opening in this compound.