Effect of ion beam irradiation on studies of surface magnetism via capture of spin-polarized electrons from a thin Co film on Cu(0Â 0Â 1)

The magnetism of ultrathin Co films deposited on a Cu(0 0 1) substrate is studied via capture of spin-polarized electrons into the He I 3p 3P term after grazing scattering of 25 keV He+ ions. For films of 5 ML we explore the effect of ion beam irradiation on the data and investigate the removal of film atoms by incident ions via Auger electron spectroscopy. From our work we deduce sputtering yields for bombardment of the film surface with He+ and Ar+ ions and determine the regime of ion fluences where the method of electron capture is applicable for studies on surface magnetism of ultrathin films.