Effects of Y- And La-doping on the magnetic ordering, Kondo effect, and spin dynamics in Ce_1-x M_xRu₂Al₁₀

The influence of Y- and La-substitution for Ce on the competing Kondo effect and magnetic ordering, as well as on spin dynamics in the Kondo semiconductor CeRu2Al10 have been investigated by means of thermal, electronic, and magnetic properties. The parent compound CeRu2Al10 is known to be a controversial antiferromagnet with high magnetic ordering temperature T 0 = 27 K. A small negative chemical pressure caused by La-doping results rapid suppression of T 0 and spin gap energy Δ m , compared to a small positive pressure caused by Y-doping. Upon Y- and La-doping, the electrical resistivity ρ(T) illustrates the evolution from dense Kondo semiconductor to incoherent single-ion Kondo behaviour, and hence weakens the c-f hybridization and thus lowers the Kondo temperature. The 5% Y- and La-doped compounds show enormous enhancement in the thermoelectric power and complex behaviour in the Hall resistivity below T 0 due to an abrupt change in charge carrier mobility with temperature. The magnetic contribution to electrical resistivity ρ mag(T) (⪆50% La) and specific heat C P(T)/T (⪆70% La) evidence non-Fermi-liquid behaviour at low temperature in the La-doped system, due to interplay of atomic disorder with spin-fluctuation. Application of magnetic field suppresses the spin-fluctuation in C P(T)/T and eventually emerges to Fermi-liquid state in the 95% La-doped compound in 9 T. The magnetic phase diagram illustrates that the strength of the Kondo interaction in the doped systems are primarily controlled by the effect of volume change as described by the compressible Kondo lattice model. We ascribe the fascinating observation of T K ≃ 4T 0 to anisotropy in the single-ion crystal electric field in the presence of strong anisotropic c-f hybridization.