Long-range ferromagnetic order of Ni-O overlayers studied by quadrupolar resonant photoemission

The resonant photoemission decay from the Ni 2p x-ray absorption of ferromagnetic nickel can be decomposed into contributions from the monopole and the quadrupole moment of the core hole with substantially different signals for each of the final-state LS-terms. The quadrupole moment induces an anisotropic contribution to the photoelectron distribution which can be used to identify the different final-state d(n) configurations in Ni and to separate substrate and overlayer signals on the Ni(110)-(3 x 1) O surface. The results provide evidence for a long-range ferromagnetic ordering in the Ni-O overlayer.