Transport properties and magnetic behaviour of Ce₈Pd₂₄Al_x (0.1≤x≤2)

Measurements are presented on the resistivity ρ(T), magnetoresistivity MR, dc susceptibility χ(T) and magnetization σ(μ₀H), of the alloy series Ce₈Pd₂₄Al_x with 0.1 ≤ x ≤ 2. Rietveld analysis of the X-ray diffraction (XRD) data indicates that Ce₈Pd₂₄Al crystallizes in the cubic structure with space group Pm3m (No. 221). The crystal structure of this compound is composed of 8 cubes of CePd₃ in which the Al atoms occupy the centres of only certain octahedrons of Pd atoms. The CAILS - Pawley (cell and intensity least square) analysis of XRD data of all compositions show that the cubic structure of the parent compound CePd₃ is retained. The XRD analysis indicate a linear increase in the cubic unit cell volume up to x = 1, followed by a curvature for larger Al concentrations and a tendency towards saturation on approaching x = 2. Measurements in the Al-poor alloy in the temperature range 4.2-300 K indicate an evolution from the intermediate valence state of Ce₈Pd₂₄ to Kondo behaviour with increased Al concentration. MR measurements on selected alloys are interpreted within the single-ion Bethe ansatz description and values of the Kondo temperature are calculated. χ(T) follows a Curie-Weiss behaviour with high-temperature effective moment values slightly reduced from the expected value of 2.54 μ_B of the free Ce³⁺-ion. The paramagnetic Weiss constant temperature -θ_p decreases rapidly with increasing Al content x, in line with the evolution from intermediate valence state to Kondo state. Low-temperature χ(T) data indicate antiferromagnetic ordering for the concentration range of 0.96 ≤ x ≤ 2. A Kondo and magnetic phase diagram for the Ce₈Pd₂₄Al_x system is presented.