Spin polarization of photoelectrons from the 5d shell of polarized Gd atoms: Application to the Gd 5d(z)2 surface state

The angular distribution of photoelectrons with defined spin orientation ej ected from the 5d(3/2) Shell of polarized Gd atoms has been investigated th eoretically. For free-atom calculations, a particular geometry of the exper iment was chosen where the direction of the light beam is parallel (or anti parallel) to the direction of atomic polarization n. In this particular cas e, the angular distributions are the functions of the electron ejection ang le theta relative to the direction n. In addition, we implied that the ligh t is circularly polarized because in this case the degree of spin polarizat ion is the highest. The calculations have been performed for the Gd ground state 4f(7)5d(D-9) in the nonrelativistic Hartree-Fock approximation, and m any-electron correlation has been included using the random-phase approxima tion with exchange as developed for open-shell atoms. It is shown that in n ormal emission the photoelectron spin polarization has a well-defined value independent of photon energy, which is different for different kinds of al ignment or orientation. The dependences of photoelectron spin polarization on the ejection angle are presented for different kinds of atomic polarizat ion. The results can be applied to the investigation of the surface state o f solid Gd that is known to be the 5d state, but not much is known about th e character of this state. The influence of scattering from neighboring ato ms on the results of the atomic calculations is investigated within a spin- dependent single scattering approximation in a two-step photoemission model . The calculations correspond to an experimental geometry with normal light incidence and to the polarization of the 5d electron being either in the d irection of the surface normal or in the surface plane. It is shown that th e results of the atomic model are strongly modulated by scattering processe s. Some of the main peculiarities remain unchanged, but certain features ar ise that cannot be predicted in pure atomic theory.