Interfacial chemistry meets magnetism: Comparison of Co/Fe3O4 and Co/α-Fe2O3 epitaxial heterostructures

• The role of biphase reconstruction in shaping Co–magnetite and Co–hematite interfaces has been revealed. • A fraction of the Co monolayer is oxidized at the interface with iron oxides. • Reduction of hematite by the Co overlayer leads to the emergence of uncompensated Fe spins at the antiferromagnetic surface. • The orbital magnetic moments of the ultrathin Co films are enhanced to as much as 0.47 μ B . The magnetic and chemical structure of metal/oxide interfaces were studied in cobalt/magnetite (Fe 3 O 4 ) and cobalt/hematite (α-Fe 2 O 3 ) epitaxial heterostructures using the comprehensive selection of microscopic and spectroscopic methods. It was observed that the cobalt nanostructures and ultrathin films were oxidized at both interfaces, with a thicker cobalt oxide layer in the system with hematite. The formation of cobalt oxides was accompanied by the interfacial reduction of iron that modified magnetic properties of the iron oxides layers. In particular, uncompensated magnetic moments appear in antiferromagnetic hematite, and the orbital magnetic moment of Co grown on magnetite is significantly enhanced for thicknesses below 1 nm. Synchrotron magnetic microscopy showed a direct correlation in the domain structures of the cobalt/iron oxides: ferromagnetic coupling between cobalt and magnetite and between cobalt and the magnetically modified layer of hematite.