Neutron scattering studies of an antiferromagnetic Kondo compound: Ce₈Pd₂₄Ga

The antiferromagnetic Ce₈Pd₂₄Ga with T_N = 3.1 K has been investigated using neutron diffraction, inelastic neutron scattering, electrical resistivity, magneto-resistance and magnetic susceptibility measurements. Rietveld analysis of neutron diffraction data reveals that Ce₈Pd₂₄Ga crystallizes in the cubic structure with space group Pm3̄m. Inelastic neutron scattering (INS) studies show two well-defined crystal-field excitations at 3.2 meV and 12.8 meV. The crystal-field parameters have been estimated from the analysis of INS data. The heat capacity calculated from the crystal-field level scheme shows a Schottky peak at 15 K which agrees well with the reported experimental results. The resistivity exhibits - ln T behaviour at high temperature followed by a peak at 8 K and eventually drops at T_N. The peak in the resistivity at 8 K arises due to the combined effect of crystalline electric fields and Kondo interactions. The analysis of the resistivity data in the magnetically ordered state reveals a gap of 16.1 K in the spin-wave spectrum. At 1.8 K the magnetoresistance is positive and it changes to negative at 3 K. The positive magnetoresistance at 1.8 K is consistent with the antiferromagnetic ground state. The negative magnetoresistance shows a scaling behaviour that yields a low-temperature Kondo temperature of 5.8 K. The magnetic susceptibility exhibits Curie-Weiss behaviour between 20 K and 300 K with an effective paramagnetic moment μ_eff = 2.33 μ_B and paramagnetic Curie temperature θ_p = -18.8 K. The present studies reveal that the physical properties of Ce₈Pd₂₄Ga are governed by the Kondo, crystal-field and Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions.