Insights into the structural, electronic, and magnetic properties of Fe2−x Ti x O3/Fe2O3 thin films with x = 0.44 grown on Al2O3 (0001)

• Published in: Journal of materials science 2015-01, 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: Aluminum oxide; Antiferromagnetism; Domains; Electron energy loss spectroscopy; Energy dissipation; Epitaxial growth; Ferrimagnetism; Hematite; Ilmenite; Iron oxides; Magnetic properties; Materials science; Molecular beam epitaxy; Organic chemistry; Substrates; Thickness; Thin films; X-ray diffraction
• ISSN: 0022-2461; 1573-4803
• DOI: 10.1007/s10853-014-8572-x

The interface between hematite (α-Fe2IIIO3) and ilmenite (FeIITiO3), 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 Fe2−xTixO3 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 \[ (0001) _{{{\text{Fe}}_{2} {\text{O}}_{3} }} \;||\;(0001) _{{{\text{Al}}_{2} {\text{O}}_{3} }}, \] one with \[ [10\bar{1}0]_{{{\text{Fe}}_{2} {\text{O}}_{3} }} \;||\;[10\bar{1}0]_{{{\text{Al}}_{2} {\text{O}}_{3} }}, \] and a twin domain with \[ [01\bar{1}0]_{{{\text{Fe}}_{2} {\text{O}}_{3} }} \;||\;\;[10\bar{1}0]_{{{\text{Al}}_{2} {\text{O}}_{3} }}. \] Electron energy loss spectroscopy profiles across the Fe2−xTixO3/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 Fe2−xTixO3/α-Fe2O3/Al2O3 system compared to the pure α-Fe2O3/Al2O3 system.