Antiferromagnetic ordering and magnetic structure of the layered cerium carbide halides, Ce2C2X2 (X = Br,I)

The compounds Ce2C2X2 (X=Br,I) crystallize with a layered structure consisting of a close-packed arrangement of X-Ce-Ce-X slabs. C2 units are located within Ce6 octahedral interstices. Depending on the stacking sequence there exist two phases (1s- and 3s-stacking variants). Powder magnetic susceptibility measurements show antiferromagnetic ordering below 13 K for Ce2C2Br2 and 15 K for Ce2C2I2. We have performed neutron powder diffraction experiments on the two samples, Ce2C2X2 (X=Br,I). From the Rietveld refinement of the low-temperature diffractograms we derive the magnetic structure of Ce2C2I2 which can be indexed by a propagation vector k=(0, 0, 1/2). (orig.)