Origin of the Giant Magnetic Moments of Fe Impurities on and in Cs Films

We have explored the origin of the observed giant magnetic moments ( $\sim 7{\mu }_B$) of Fe impurities on the surface and in the bulk of Cs films, using the relativistic local-spin-density-approximation method. We have found that Fe impurities in Cs behave differently from those in noble metals or in Pd. Whereas the induced spin polarization of Cs atoms is negligible, the Fe ion itself is a source of the giant magnetic moment. The $3d$ electrons of Fe in Cs are localized as the $4f$ electrons in rare-earth ions so that the orbital magnetic moment becomes as large as the spin magnetic moment. The calculated total magnetic moment $M=6.43\mathrm{}{\mu }_B$ is close to the experimentally observed value.