Insights into the structural, electronic, and magnetic properties of Fe2-xTixO3/Fe2O3 thin films with x=0.44 grown on Al2O3 (0001)

The interface between hematite (alpha-(Fe2O3)-O-III) and ilmenite ((FeTiO3)-Ti-II), 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 (similar to 25 nm thickness) of alpha-Fe2O3 on alpha-Al2O3 (0001) substrates, which were capped with a similar to 25 nm thick Fe2-xTixO3 layer (x = 0.44). An additional 3 nm cap of alpha-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 (0001)(Fe2O3) vertical bar vertical bar (0001)(Al2O3,) one with [10 (1) over bar0](Fe2O3) vertical bar vertical bar [10 (1) over bar0](Al2O3), and a twin domain with [01 (1) over bar0](Fe2O3) vertical bar vertical bar [10 (1) over bar0]Al2O3. Electron energy loss spectroscopy profiles across the Fe2-xTixO3/Fe2O3 interface show that FeFe2+/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 Fe2-xTixO3/alpha-Fe2O3/Al2O3 system compared to the pure alpha-Fe2O3/Al2O3 system.