Insights into the structural, electronic, and magnetic properties of Fe_2−xTi_xO₃/Fe₂O₃ thin films with x = 0.44 grown on Al₂O₃ (0001)

The interface between hematite (α-Fe₂ ^IIIO₃) and ilmenite (Fe^IITiO₃), a weak ferrimagnet and an antiferromagnet, respectively, has been suggested to be strongly ferrimagnetic due to the formation of a mixed valence layer of Fe²⁺/Fe³⁺ (1:1 ratio) caused by compensation of charge mismatch at the chemically abrupt boundary. Here, we report for the first time direct experimental evidence for a chemically distinct layer emerging at heterointerfaces in the hematite—Ti-doped-hematite system. Using molecular beam epitaxy, we have grown thin films (~25 nm thickness) of α-Fe₂O₃ on α-Al₂O₃ (0001) substrates, which were capped with a ~25 nm thick Fe_2−xTi_xO₃ layer (x = 0.44). An additional 3 nm cap of α-Fe₂O₃ was deposited on top. The films were structurally characterized in situ with surface X-ray diffraction, which showed a partial low index orientation relationship between film and substrate in terms of the [0001] axis and revealed two predominant domains with (Formula presented.) one with (Formula presented.) and a twin domain with (Formula presented.). Electron energy loss spectroscopy profiles across the Fe_2−xTi_xO₃/Fe₂O₃ interface show that Fe²⁺/Fe³⁺ ratios peak right at the interface. This strongly suggests the formation of a chemically distinct interface layer, which might also be magnetically distinct as indicated by the observed magnetic enhancement in the Fe_2−xTi_xO₃/α-Fe₂O₃/Al₂O₃ system compared to the pure α-Fe₂O₃/Al₂O₃ system.