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

Abstract

Three samples of nominal compositions CeFe 9Si 2C x ( 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 BaCd 11-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 CeFe 9.8Si 1.2C x. At 2 K, a significant difference is observed in the Fe moment amplitudes between the 32(i) site ( μ Fe ∼ 1.6 μ B ) on the one hand, and the 4(b) ( μ Fe ∼ 3.0 μ B ) and 8(d) sites ( μ Fe ∼ 2.5 μ B ) 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.