Study of electronic structure and valence state of CeCo$_{2}$ nanoparticles

We have performed the Ce L$_{3}$-, M$_{4,5}$-edge and Co L$_{2,3}$-, K-edge x-ray absorption measurements to investigate the dependence of valence state and local electronic structures on different particles size of CeCo$_{2}$. By monitoring the modifications in Ce L$_{3}$- and M$_{4,5}$-edges XAS spectra shape, the individual intensities of the two valence states reflect the mixed configuration in the ground state in CeCo$_{2}$. The Ce in nanopartice CeCo$_{2}$ exhibits mixed valence with only small amount of tetravalent Ce, which is in contrast to the bulk. Combination with the results observed from the Co L$_{2,3}$-, K-edge, reduced in valence for nanoparticles can be interpreted in terms of surface effects and gives rise to weaker hybridization between the Co 3d and Ce 4f-5d states.