Journal of Alloys and Compounds 391 (2005) 8–12 A magnetic, neutron diffraction and X-ray absorption spectroscopy study of Ce(Fe, Si) 11 C x compounds (x = 0.5, 1.0, 1.5) V. Klosek a, ∗ , O. Isnard a, b a Laboratoire de Cristallographie du CNRS, Associ´ e` a l’Universit´ e Joseph Fourier et ` a l’INPG, Avenue des Martyrs, BP166X, F-38042 Grenoble Cedex 9, France b Institut Universitaire de France, Maison des Universit´ es, 103 Boulevard Saint Michel, F-75005 Paris Cedex, France Received 2 June 2004; received in revised form 26 August 2004; accepted 26 August 2004 Available online 12 October 2004 Abstract Three samples of nominal compositions CeFe 9 Si 2 C 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 9.8 Si 1.2 C x . At 2 K, a significant difference is observed in the Fe moment amplitudes between the 32(i) site (μ Fe ∼ 1.6μ B ) on the one hand, and the 4(b) (μ Fe ∼ 3.0μ B ) and 8(d) sites (μ Fe ∼ 2.5μ 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. © 2004 Elsevier B.V. All rights reserved. PACS: 75.50.Bb; 61.10.Ht; 61.12.Ld; 71.28.+d Keywords: Rare earth-3d transition metal compounds; Magnetic measurements; Neutron powder diffraction; X-ray absorption spectroscopy; Ce intermediate valence state 1. Introduction Since the discovery of the highly interesting permanent magnet properties of Nd 2 Fe 14 B [1], Fe-rich intermetallic compounds involving rare earth elements R have been the subject of numerous experimental and theoretical studies. Most of them have been devoted to compounds with the ThMn 12 -type structure, as the RFe 12-x M x compounds (M = Ti, V, Cr, Mo, W, Si) [2], or to interstitially modified R 2 Fe 17 compounds [3] with promising magnetic properties. In the search for new materials, the attention was focussed on the ∗ Corresponding author. Present address: CEA, Centre de Valduc, F-21120 Is-sur-Tille, France. Tel.: +33 380 23 65 87; fax: +33 380 23 52 17. E-mail address: Vincent.Klosek@cea.fr (V. Klosek). 1:11 stoichiometry. Unfortunately, RFe 11 compounds are not stable. As Bodak et al. managed earlier to obtain a NdCo 9 Si 2 compound with the tetragonal BaCd 11 -type structure [4], at- tempts were made to prepare some RFe 9 Si 2 compounds, but without success. Later, by adding small amounts of carbon, Le Roy et al. obtained RFe 10 SiC 0.5 compounds (R = Ce, Pr, Nd, Sm) which crystallise in a filled variant of the BaCd 11 structure [5]. More recently, Zhang et al. reported the synthe- sis of some RFe 9 Si 2 C x compounds (R = Ce, Pr, Nd, Sm; x = 0.5, 1.0, 1.5) [6] and focussed their attention on the magnetic properties of the Nd compounds for which first-order mag- netisation processes were evidenced [7]. In a previous paper [8], we investigated the structural and magnetic properties of some Pr(Fe, Si) 11 C x compounds with x ∼ 0.5, 1.0, 1.5. We logically decided to perform the same type of study on Ce(Fe, Si) 11 C x compounds. 0925-8388/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2004.08.044