Interplay of antiferromagnetism and Kondo effect in (Ce_1−xLa_x)₈Pd₂₄Al

The interplay of antiferromagnetic (AFM) and Kondo effect in Ce₈Pd₂₄Al with the dilution of Ce with La is investigated by means of electrical and thermal transport and magnetic properties measurements. X - ray diffraction studies confirm a cubic AuCu₃ - type crystal structure with space group Pm3¯m for all compositions in the alloy series (Ce_1−xLa_x)₈Pd₂₄Al (0≤x≤1). Electrical resistivity, ρ(T) results show evolution from coherent Kondo lattice scattering with a well defined Kondo peak at T_max to incoherent single-ion Kondo scattering with increasing La content x. Magnetoresistivity MR measurements on Ce dilute alloys are negative and analyzed based on the calculations by Schlottmann for the Bethe - ansatz in the framework of the Coqblin - Schrieffer model and yield values of the Kondo temperature T_K and the effective moment of the Kondo ion μ_K. The decrease of T_max and T_K is described by the compressible Kondo lattice model. The thermoelectric power, S(T) measurements are interpreted within the phenomenological resonance model. The Lorentz number, L/L₀ increases rapidly on cooling the samples and reaches a maximum value around 6 K. The magnetic susceptibility, χ(T) data at high temperature follow the Curie - Weiss behaviour and yield effective magnetic moments, μ_eff values across the series close to the value of 2.54 μ_B expected for the free Ce³⁺ - ion. The low temperature χ(T) shows an AFM anomaly associated with a Néel temperature T_N for alloys in the range 0≤x≤0.2. No metamagnetic transition was observed from the magnetization results, M(μ₀H).