Combined spectroscopic and ab initio investigation of monolayer-range Cr oxides on Fe(001) : the effect of ordered vacancy superstructure

We investigated the electronic structure of an ultrathin Cr oxide film prepared by growing about 0.8 monolayers of Cr on the oxygen-terminated Fe(001)−p(1×1)O surface and characterized by the formation of an ordered array of Cr vacancies producing a (√5×√5)R27∘ superstructure. We combined experimental techniques such as angle- and spin-resolved photoemission spectroscopy, low-energy electron diffraction, and scanning tunneling spectroscopy with ab initio calculations, focusing on (i) the peculiar energy dispersion of O2p states and (ii) the orbital and spin character of Cr3d states. We show that the experimental O2p dispersion can be related to the presence of an ordered vacancy lattice. The comparison with the existing literature on the oxidation of bulk Cr(001), where a network of Cr vacancies with a short-range crystallographic order is present, reveals a similar effect on O states. The valence electronic structure of the Cr oxide layer is mostly composed by spin-minority Cr states, consistent with an antiferromagnetic coupling with the Fe substrate.