Electronic structure of Eu?C70 fullerides

The electronic structure of Eu-intercalated C70 has been studied by a synchrotron radiation photoemission spectroscopy technique. At low intercalation levels (below the stoichiometry of Eu3C70), the photoemission data clearly exhibit charge transfer from Eu 6s states to the lowest-unoccupied-molecular-orbital (LUMO) and the LUMO + 1 of C70. The amount of charge transfer reaches its maximum far before intercalation saturation. Detailed analysis reveals that most of the 5d6s electrons of Eu occupy the so-called interstitial states in the saturation phase (Eu9C70). The interstitial states are induced by a Eu sub-lattice formed at heavy intercalation levels, and comprise substantial 6s-π hybridized states. The π states participating in the hybridization are mainly the HOMO − n (n = 6–10) orbitals. The PES data also reveal the semiconducting property for both Eu3C70 and Eu9C70. The 6s–(HOMO − n) hybridization and the semiconducting property should play important roles in understanding the ferromagnetic mechanism for Eu9C70.