LOCAL MAGNETISM AND ELEMENT-SPECIFIC SUSCEPTIBILITY FOR NI CU(100)/

We report magnetic circular X-ray dichroism (MCXD) measurements of ult rathin Ni films grown on Cu(?OO). The Curie temperature of the films i s determined by means of a.c. MXCD susceptibility, a technique that al lows T-c to be probed precisely and unambiguously. Furthermore, the in teraction of submonolayer oxygen with the films, adsorbed in physisorb ed molecular and atomic states, is studied. The decrease in the magnet ic response of the sample is investigated systematically for various a dsorption states of increasing chemisorption strength. The oxygen indu ced changes in the MCXD difference and in the absorption features meas ured with linear polarized light provide a better characterization of the electronic states involved in the MCXD response. The magnetism of the Ni films is already influenced by O-2 molecules in a physisorbed s tate, a c(2 x 2) overlayer of atomic oxygen is found to neutralize the magnetism of two layers of an ultrathin Ni film.