Cd doping effects in the heavy-fermion compounds Ce2MIn8 (M = Rh and Ir)

Low-temperature magnetic properties of Cd-doped Ce2MIn8 (M = Rh and Ir) single crystals are investigated. Experiments of temperature-dependent magnetic-susceptibility, heat-capacity, and electrical-resistivity measurements revealed that Cd doping enhances the antiferromagnetic (AFM) ordering temperature from T-N = 2.8 K (x=0) to T-N=4.8 K (x=0.21) for Ce2RhIn8-xCdx and induces long-range AFM ordering with T-N = 3.8 K (x=0.21) for Ce2IrIn8-xCdx. Additionally, x-ray and neutron magnetic scattering studies showed that Cd-doped samples present below T-N a commensurate antiferromagnetic structure with a propagation vector (epsilon) over right arrow=(1/2, 1/2, 0). The resolved magnetic structures for both compounds indicate that the Cd doping tends to rotate the direction of the ordered magnetic moments toward the ab plane. This result suggests that the Cd doping affects the Ce3+ ground-state single-ion anisotropy modifying the crystalline electrical field (CEF) parameters at the Ce3+ site. Indications of CEF evolution induced by Cd doping were also found in the electrical-resistivity measurements. Comparisons between our results and the general effects of Cd doping on the related compounds CeMIn5 (M=Co, Rh, and Ir) confirms the claims that the Cd doping induced electronic tuning is the main effect favoring AFM ordering in these compounds.