Epitaxial films along the Fe${}_{3-x}$Ti${}_x$O${}_4$ (titanomagnetite) compositional series from pure end-members magnetite (Fe${}_3$O${}_4$) to ulvöspinel (Fe${}_2$TiO${}_4$) were successfully grown by pulsed laser deposition on MgO(001) substrates. Characterization, including high-resolution x-ray diffraction, x-ray photoelectron spectroscopy, and synchrotron-based x-ray absorption and magnetic circular dichroism, consistently shows that Ti(IV) substitutes for Fe(III) in the inverse spinel lattice with a proportional increase in lattice Fe(II) concentration. No evidence of Ti interstitials, spinodal decomposition, or secondary phases was found in the bulk of the grown films. At the uppermost few nanometers of the Ti-bearing film surfaces, evidence suggests that Fe(II) is susceptible to facile oxidation and that an associated lower Fe/Ti ratio in this region is consistent with surface compositional alteration to a titanomaghemite-like composition and structure. The surfaces of these films nonetheless appear to remain highly ordered and commensurate with the underlying structure despite facile oxidation, a surface condition that is found to be reversible to some extent by heating in low-oxygen environments.

• Received 21 February 2011

DOI:https://doi.org/10.1103/PhysRevB.84.125443