Resonant x-ray scattering study of layered TbBaCo 2 O 5.5

Resonant x-ray scattering (cid:1) RXS (cid:2) experiments have been performed at the Co K edge in the TbBaCo 2 O 5.5 sample. Linear scans in the reciprocal space along (cid:3) 0 k 0 (cid:4) and (cid:3) h 00 (cid:4) directions were carried out at different energies between 350 and 90 K. This temperature range probes the metallic, insulating, ferrimagnetic, and antiferromagnetic phases. No new reflections, either resonant or not, were detected in any phase transition. We have found strong resonances close to the absorption edge energy for (cid:1) 0 k 0 (cid:2) reflections with k odd. These resonances remain almost constant for the different phases. The cusp of the resonant scattering is either up— (cid:1) 0 3 0 (cid:2) and (cid:1) 0 7 0 (cid:2) —or down— (cid:1) 0 1 0 (cid:2) and (cid:1) 0 5 0 (cid:2) —depending on the k value, and this behavior was completely explained in the frame of the crystal structure and the atomic position of the Tb and Ba atoms. The occurrence of the resonant scattering and its azimuthal behavior has been explained in terms of the anisotropy of the tensor of susceptibility (cid:1) ATS reflections (cid:2) . RXS comes from the presence of two different environments for the Co ions, octahedra and pyramids of oxygens, ordered along the b axis. No evidence for further contributions, such as an orbital ordering, has been found in these experiments in the insulating low temperature phase.