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

• Published in: Journal of materials science 2015, Vol.50 (1), p.122-137
• Main Authors: Dennenwaldt, Teresa, Lübbe, Maike, Winklhofer, Michael, Müller, Alexander, Döblinger, Markus, Nabi, Hasan Sadat, Gandman, Maria, Cohen-Hyams, Tzipi, Kaplan, Wayne D., Moritz, Wolfgang, Pentcheva, Rossitza, Scheu, Christina
• Format: Article
• Language: English
• Subjects: Characterization and Evaluation of Materials; Chemistry and Materials Science; Classical Mechanics; Crystallography and Scattering Methods; Materials Science; Original Paper; Polymer Sciences; Solid Mechanics
• ISSN: 0022-2461; 1573-4803
• DOI: 10.1007/s10853-014-8572-x

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 2 O 3 | | ( 0001 ) Al 2 O 3 , one with [ 10 1 ¯ 0 ] Fe 2 O 3 | | [ 10 1 ¯ 0 ] Al 2 O 3 , and a twin domain with [ 01 1 ¯ 0 ] Fe 2 O 3 | | [ 10 1 ¯ 0 ] Al 2 O 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.