Physica B 312–313 (2002) 226–227 Investigation of antiferromagnetic ground state of CeðFe 0:93 Co 0:07 Þ 2 L. Paolasini a, *, B. Ouladdiaf b , G.H. Lander c , N. Bernhoeft d , P. Canfield e a European Synchrotron Radiation Fac., BP 220, F-38043 Grenoble Cedex, France b Institut Laue Langevin, BP 156, 38042 Grenoble, France c EITU, JRC, Postfach 2340, D-76125 Karlsruhe, Germany d DRFMC, SPSMS, CEA-Grenoble, 38054 Grenoble, France e Ames Laboratory and Iowa State University, Ames, IA 50011, USA Abstract Resonant X-ray magnetic scattering experiments have been performed on a single crystal of CeðFe 0:93 Co 0:07 Þ 2 : With small Co doping the antiferromagnetic state is stabilized at low temperature, together with a rhombohedral distortion. We show by the azimuthal dependence of the scattered X-ray intensity at the L 3 edge of Ce that the Ce moments appear to lie parallel to the rhombohedral axis of distortion of the single domain probed. This result would be in disagreement with the accepted collinear spin arrangement from neutron-diffraction experiments. As a result, we re-analyze the neutron data to show that a possible model consistent with both experimental results involves a non-collinear arrangement of Fe spins. Introducing the dynamical aspect of this concept into the physics of CeFe 2 may allow one to understand how the frustration of the Fe tetrahedra leads to the appearance of antiferromagnetic fluctuations in the presence of ferromagnetism. r 2002 Elsevier Science B.V. All rights reserved. Keywords: Itinerant magnetism; Resonant X-ray magnetic scattering; Laves phases Since the late 1980s CeFe 2 has been studied exten- sively as a classical itinerant magnetic system in which the Ce 4f and 5d and the Fe 3d electrons are strongly hybridised [1]. One of the surprises in the inelastic scattering experiments on CeFe 2 was the discovery of finite frequency antiferromagnetic (AF) fluctuations in an otherwise normal ferromagnet [2]. These occurred at the same position, Q 0 ¼ð 1 2 ; 1 2 ; 1 2 Þ as the known AF order in doped CeFe 2 [3]. The AF structure of this state in the doped materials has been deduced from neutron experiments on polycrystalline samples and is charac- terised by the Fe spins (no statistically significant moment could be established on the Ce site) lying on a cone (with axis ½111 and half-angle f) defined by sin 2 f ¼ 2 3 ; i.e. the Fe moments cannot be aligned along the propagation direction (sin 2 fa0), and a collinear structure was assumed. Resonant X-ray magnetic scattering (RXMS) experi- ments were performed at Ce L 3 edge ðE ¼ 5:720 keVÞ on the ID20 beamline of the ESRF on a single crystal of CeðFe 0:93 Co 0:07 Þ 2 grown by flux method at Ames Laboratory. The experimental configuration provides linear polarized light perpendicular to the scattering plane (s) and an incident energy resolution of 0:8 eV: An LiFð220Þ crystal was used to analyze the polarization of the scattered beam. CeðFe 1x Co x Þ 2 crystallizes in the cubic Laves phase C15 structure (space group Fd % 3m) with a 0 ¼ 7:296 ( A at 300 K: A thin slice of material with a ð111Þ face as specular direction was cooled to 10 K by using a closed-cycle refrigerator. The size of the incident beam enabled a single domain to be selected in the low-T rhombohedral phase below T N ¼ 69 K: Fig. 1 shows the enhancement of magnetic signal at the ð 5 2 ; 5 2 ; 5 2 Þ reciprocal lattice position in the s  p 0 channel. RXMS is sensitive both to imaginary and *Corresponding author. Tel.: 0033-4-7688-2402; fax: 0033-4- 7688-2542. E-mail address: paolasin@esrf.fr (L. Paolasini). 0921-4526/02/$-see front matter r 2002 Elsevier Science B.V. All rights reserved. PII:S0921-4526(01)01088-2