MODIFICATIONS OF THE ELECTRONIC AND MAGNETIC-PROPERTIES OF ULTRATHIN NI CU(100) FILMS INDUCED BY STEPWISE OXIDATION/

We report near-edge x-ray-absorption fine-structure (NEXAFS) and magne tic circular x-ray dichroism (MCXD) measurements of 4-ML Ni films grow n on Cu(100). The films were exposed to oxygen which then adsorbed in different adsorption states. The changes in the density of states as p robed at the Ni L(2,3) edges, the oxygen K edge, as well as the magnet ic response of the sample are investigated simultaneously for the vari ous adsorption states that range from O-2/Ni at 38 K to an ultrathin f ilm of NiO. The NEXAFS spectra provide a characterization of the chang es in the different nickel 3d, 4sp, and oxygen 2p density of states ab ove the Fermi level. These states dominate the interaction of the oxyg en and nickel atoms and can be studied separately using the element sp ecificity of x-ray absorption. We find that 0.5 ML of atomic oxygen su ppresses the magnetization corresponding to one layer of Ni, and for 1 .5 ML no ferromagnetic response from a 4-ML film at 38 K could be dete cted.