Air-Resistant Titanium Oxide Capping for Graphene/Ferromagnet Heterostructures

Graphene/ferromagnet interfaces have widely demonstrated the capability to host peculiar magnetic and electronic properties relevant for spintronic devices. In principle, besides strengthening perpendicular magnetic anisotropy (PMA) and sizable Dzyaloshinskii–Moriya interaction (DMI), graphene provides an additional advantage by acting as a protective layer against oxidation of the underlying metal film. However, the structural imperfections of graphene, often resulting from its growth conditions, can facilitate intercalation, which can compromise the underlying ferromagnetic layer. To address this issue, here, the use of a titania capping layer as a protective barrier for a heterostructure consisting of monolayer graphene grown on a thin cobalt film is proposed. The results demonstrate that the titanium oxide layer does not alter the properties of the interface, as confirmed by X-ray photoemission spectroscopy (XPS) and X-ray magnetic circular dichroism (XMCD) imaging. Furthermore, magneto-optic Kerr effect (MOKE) measurements reveal that the interface's magnetic properties remain stable after prolonged exposure to ambient conditions. Absorption profile simulations show that the capping layer is transparent to visible wavelengths, demonstrating its capability to enable optical studies of atomic interfacial effects without the need for an ultra-high vacuum (UHV) environment. These findings position titanium oxide as a robust, non-invasive capping material for graphene-based spintronic heterostructures.