Insights into the structural, electronic, and magnetic properties of Fe 2− x Ti x O 3 /Fe 2 O 3 thin films with x = 0.44 grown on Al 2 O 3 (0001)

The interface between hematite (α-Fe 2 III O 3 ) and ilmenite (Fe II TiO 3 ), a weak ferrimagnet and an antiferromagnet, respectively, has been suggested to be strongly ferrimagnetic due to the formation of a mixed valence layer of Fe 2+ /Fe 3+ (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-Fe 2 O 3 on α-Al 2 O 3 (0001) substrates, which were capped with a 25 nm thick Fe 2− x Ti x O 3 layer ( x = 0.44). An additional 3 nm cap of α-Fe 2 O 3 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) _Fe_2O_3 || (0001) _Al_2O_3, one with [101̅0]_Fe_2O_3 || [101̅0]_Al_2O_3, and a twin domain with [011̅0]_Fe_2O_3 || [101̅0]_Al_2O_3. Electron energy loss spectroscopy profiles across the Fe 2− x Ti x O 3 /Fe 2 O 3 interface show that Fe 2+ /Fe 3+ 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− x Ti x O 3 /α-Fe 2 O 3 /Al 2 O 3 system compared to the pure α-Fe 2 O 3 /Al 2 O 3 system.