Valence state of Eu ions in C-60 fullerides

摘要

We have prepared Eu-intercalated C-60 films in ultra-high vacuum, With special attention to avoid oxygen contamination. X-ray photoelectron spectra were measured in situ. Eu 4f photoemission reveals that the valence state of Eu ions is divalent for all intercalation levels. C 1s photoemission exhibits evidence of both ionic and covalent contributions to the Eu-C-60 bonding. The results eliminate the controversy about the valence state of Eu ions in the literature, and can help to understand the ferromagnetism (FM) and the giant magnetoresistance (GMR) of Eu6C60.