Oxygen contribution to the magnetic response of ultrathin Fe/Ni multilayers grown on Fe-p(1x1)O

We investigated the magnetic behaviour of an Fe overlayer on a Ni buffer layer (Fe/Ni multilayer system) grown on top of the Fe-p(1×1)O surface, with a particular focus on the modifications observed in the spin-resolved electronic structure and the role of oxygen, introduced in the system in a well-defined amount at the substrate preparation stage. The structural properties are investigated by means of low energy electron diffraction, that confirms the formation of an epitaxial system featuring a metastable surface lattice. Spin-resolved photoemission spectroscopy testifies a strong decrease of the spectral spin polarization for increasing thickness of the Ni buffer layer, reaching a minimum from a nominal thickness of 6 Ni atomic layers. Surprisingly, the growth of a single Fe overlayer is sufficient to restore most of the original polarization signal, thus creating an ultrathin bcc Fe film seemingly decoupled from the substrate. Ab initio calculations track the modifications of the magnetic moments of the surface layers that quench upon Ni deposition and restore with additional Fe growth. Spin-resolved inverse photoemission highlights a notable reduction of the density of majority states just above the Fermi level, possibly influencing the magnetic response of the system.