A new look at the ground state properties of Ce₂Ir₃Al₉: Coexistence of two competing energy scales

We present an extended research on characterization of the ground state in a polycrystalline compound Ce₂Ir₃Al₉ using powder x-ray diffraction, magnetic susceptibility χ(T), isothermal magnetization M(B), specific heat C_p(T), electrical resistivity ρ(T), magnetoresistivity ρ(B), thermoelectric power S(T) and thermal conductivity κ(T) measurements, together with a theoretical description of the obtained data to develop a more profound understanding of the physics in this compound. Ce₂Ir₃Al₉ crystallizes in the orthorhombic Y₂Co₃Ga₉-type of structure (space group Cmcm, No. 63, oC56, Z = 4). The χ(T) and C_p(T)/T data reveal the signatures of intermediate valence behaviour on Ce ions with the approximate value of the Kondo temperature T_K = 96 K and the Sommerfeld coefficient γ = 31 mJ/mol ⋅ K². In contrast to the magnetometric and thermodynamic measurements, the transport data (ρ(T) and S(T)) indicate the development of the Kondo lattice state. Accordingly, we expect that for Ce₂Ir₃Al₉ the most likely scenario, which develops in a wide T range is the coexistence and competition of two energy scales of interactions between conduction electrons and 4f spins on Ce ions, located in one unique crystallographic site in the unit cell, in consequence carrying out our system from Ce⁴⁺Temp.→ Ce³⁺. At higher temperatures, where the Kondo interaction becomes dominant the influence of the crystal electric field effect seems to play an influential role in the ground state of this compound too.