Localized Magnetic States of Fe, Co, Ni Impurities on Alkali Metal Films

We report X-ray magnetic circular dichroism experiments on isolated as well as clustered Fe, Co, and Ni impurities deposited on K and Na films. The results explain the origin of the giant magnetic moments in alkali metal systems. The multiplet structure of the absorption spectra clearly shows that Fe, Co, and Ni impurities have a localized ground state of ionic type with predominant $d^7$, $d^8$, and $d^9$ character, respectively. The localized impurity states correspondingly possess a large, atomic-like, magnetic orbital moment that is progressively quenched as clustering occurs. Ni on Na films is found to be nonmagnetic, with a strongly increased $d^{10}$ character of the impurity state.