Electronic structure and valence state of CeAl2 from X-ray absorption and emission spectroscopy

Soft X-ray absorption spectroscopy (XAS) and resonant inelastic X-ray scattering (RIXS) have been performed on CeAl2 bulk and nanoparticles of 8 nm to study the quantum size effect of this heavy-fermion compound. XAS and RIXS spectra recorded at selected photon energies, reflect the local unoccupied and occupied electronic states. These spectral shape changes are attributed to surface effects originated from the reducing particle size, which gives rise to different hybridization between the 4f orbitals and conduction band. The Ce in nanoparticles exhibits mixed valencies with a small portion of tetravalent Ce in contrast to the mostly trivalent Ce observed in the bulk CeAl2. RIXS spectra show a strong dependence on the excitation energies. The experimental results suggest the different f-electron configurations for bulk and nanoparticle CeAl2