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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)

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Abstract

The interface between hematite (α-Fe III2 O3) 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−x Ti x O3 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−x Ti x O3/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−x Ti x O3/α-Fe2O3/Al2O3 system compared to the pure α-Fe2O3/Al2O3 system.

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Acknowledgement

The authors C.S. and A. M. would like to thank the Deutsche Forschungsgemeinschaft (DFG) for financial support via the project SCHE634/12-1 within the priority program SPP1613. R.P., M.W. and W.M. acknowledge the DFG, Grant No PE883/4-1 (ESF EUROMISCI Program, Project MICROMAGN) and STA 1026/2-1. We thank Peter Gille and Renate Enders for their help with the preparation of the α-Al2O3 substrates, Matthias Opel and Rudolf Groß for measurement time on their SQUID magnetometer, and Alexander Gigler for help with the Raman measurements.

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Author notes

  1. Teresa Dennenwaldt, Alexander Müller & Christina Scheu

    Present address: Max-Planck-Institut für Eisenforschung, Max-Planck-Str. 1, 40237, Düsseldorf, Germany

  2. Rossitza Pentcheva

    Present address: Faculty of Physics, University of Duisburg-Essen, Lotharstr. 1, 47057, Duisburg, Germany

Authors and Affiliations

  1. Department of Chemistry and Center for NanoScience, Ludwig-Maximilians-Universität München, Butenandtstr. 5-13, 81377, Munich, Germany

    Teresa Dennenwaldt, Alexander Müller, Markus Döblinger & Christina Scheu

  2. Department of Earth and Environmental Sciences and Center for Nanoscience, Ludwig-Maximilians-Universität München, Theresienstr. 41, 80333, Munich, Germany

    Maike Lübbe, Michael Winklhofer, Hasan Sadat Nabi, Wolfgang Moritz & Rossitza Pentcheva

  3. Department of Materials Science and Engineering 210 Hearst Memorial Mining Building, University of California, Berkeley, USA

    Maria Gandman

  4. Department of Materials Science and Engineering, Technion – Israel Institute of Technology, 32000, Haifa, Israel

    Tzipi Cohen-Hyams & Wayne D. Kaplan

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  1. Teresa Dennenwaldt
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Correspondence to Christina Scheu.

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Dennenwaldt, T., Lübbe, M., Winklhofer, M. et al. 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). J Mater Sci 50, 122–137 (2015). https://doi.org/10.1007/s10853-014-8572-x

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