Effect of transition metals on the crystal field in CeCo0.4Fe0.6Ge3

We present an investigation of the influence of the 3d elements, Co and Fe, on the interactions between magnetic Ce atoms in the CeCo0.4Fe0.6Ge3 alloy, the member of the CeCo1−xFexGe3 series. The investigated alloy crystallizes in the noncentrosymmetric tetragonal BaNiSn3-type structure (space group I4mm, No. 107), in which the Co and Fe atoms occupy the same 2a position. The close vicinity to the quantum critical point for this alloy was indicated based on previous reports and confirmed by our low temperature resistivity measurements presented in this article. The role of Co and Fe atoms in this alloy was deduced from the scheme of the crystal field levels employing inelastic neutron scattering, specific heat, and magnetic susceptibility. For the analysis, samples LaCoGe3, LaFeGe3, and LaCo0.4Fe0.6Ge3 were used as non-magnetic analogs. The obtained results for CeCo0.4Fe0.6Ge3 alloy were compared with those for CeCoGe3 and CeFeGe3 compounds to emphasize the observed changes in physical properties. The specific heat results are supported by the first-principles calculations. The analysis indicated that the excitation levels of Ce ions are different for the Co- and Fe-rich neighborhood. Based on this information, we can conclude that the 3d elements provide the same energies of RKKY and Kondo interactions for the nearest Ce ions, but their energies for the further ions are lowered due to the presence of other 3d elements.