Interfacial properties between CoO (100) and Fe₃O₄ (100)

Using molecular beam epitaxy 1–20 ML thick CoO (100) films were grown monolayer by monolayer on Fe₃O₄ (100) substrates. The stoichiometry of the films was verified by low-energy-electron diffraction and reflection-high-energy-electron diffraction patterns, as well as x-ray photoelectron spectroscopy. Auger measurements as a function of CoO film thickness indicated a layer-by-layer growth mode. Ultraviolet photoelectron spectroscopy (UPS) was used to monitor the thin film electronic properties. The evolution of the density of states in the O 2p∕Fe 3d and O 2p∕Co 3d bands exhibits a shift in the position of the CoO valence band for ultrathin films relative to bulklike thick films. The measured spectra (when aligned to cancel the band shift) are compared to models of the spectra that would be expected based on the bulk compounds, with and without additional interfacial electronic states. Electronic states at the Fe₃O₄-CoO interface have been identified, and their UPS spectrum has been determined.