Phase formation and ground state properties of CeCo9Si4

The phase relations of the CeCo9+δSi4-δ system have been studied by means of scanning electron microscopy, electron microprobe analysis and x-ray diffraction. Essentially single phase samples CeCo9+δSi4-δ (structure-type LaFe9Si4 with space group I4/mcm) are formed in a narrow composition range - 0.3 ≤ δ < 0.1, where stoichiometric CeCo9Si4 exhibits full structural order in space group I4/mcm. The evolution of the ground state of correlated 3d and 4f electrons in the solid solution CeCo9+δSi4-δ has been investigated by dc susceptibility, magnetization, specific heat and resistivity measurements. Stoichiometric CeCo9Si4 exhibits paramagnetic Kondo lattice behaviour with a largely reduced Co 3d contribution to the magnetic susceptibility as compared to nearly ferromagnetic LaCo9Si4. Nonetheless, very similar to the solid solution LaCo9+δSi4-δ, weak ferromagnetism is observed in CeCo9+δSi4-δ for δ > 0 and is attributed to substitutional disorder at the Si-sublattice.