A magnetic, neutron diffraction and X-ray absorption spectroscopy study of Ce(Fe, Si)11Cx compounds (x = 0.5, 1.0, 1.5)

Three samples of nominal compositions CeFe9Si2Cx (x = 0.5, 1.0, 1.5) were prepared by arc-melting. The crystallographic structure and the magnetic properties of the obtained compounds were investigated by means of X-ray and neutron powder diffraction, and magnetic measurements. They crystallise within a filled variant of the tetragonal BaCd11-type structure, with Ce in 4(a) position and Fe in the 4(b), 32(i) and 8(d) sites, the Si atoms being located on the remaining part of the 8(d) sites and the carbon atoms occupying 8(c) octahedra formed by four Fe and two Ce atoms. From the neutron diffraction study, the composition of the x = 1.0 compound is thus found to be close to CeFe9.8Si1.2Cx. At 2 K, a significant difference is observed in the Fe moment amplitudes between the 32(i) site (μFe∼ 1.6μB) on the one hand, and the 4(b) (μFe∼ 3.0μB) and 8(d) sites (μFe∼ 2.5μB) on the other hand. No magnetic moment was detected on the Ce sublattice. So X-ray absortion experiments were performed on the three compounds to analyse the cerium valence state. They led to characterize an intermediate valence state of Ce, with a partial relocalisation of the 4f electronic orbitals when the carbon concentration increases.