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American Mineralogist; February-March; v. 94; no. 2-3; p. 262-269; DOI: 10.2138/am.2009.2989
© 2009 Mineralogical Society of America
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The application of Lorentz transmission electron microscopy to the study of lamellar magnetism in hematite-ilmenite

Takeshi Kasama1,*, Rafal E. Dunin-Borkowski2, Toru Asaka3, Richard J. Harrison4, Ryan K.K. Chong1, Suzanne A. McEnroe5, Edward T. Simpson1, Yoshio Matsui3 and Andrew Putnis6

1 Department of Materials Science and Metallurgy, University of Cambridge, Pembroke Street, Cambridge CB2 3QZ, U.K.
2 Center for Electron Nanoscopy, Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark
3 Advanced Materials Laboratory, National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan
4 Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, U.K.
5 Geological Survey of Norway, N-7491 Trondheim, Norway
6 Institut für Mineralogie, Universität Münster, Corrensstrasse 24, D-48149 Münster, Germany

Correspondence: * Present address: Center for Electron Nanoscopy, Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark. E-mail: tk{at}cen.dtu.dk

Lorentz transmission electron microscopy has been used to study fine-scale exsolution microstructures in ilmenite-hematite, as part of a wider investigation of the lamellar magnetism hypothesis. Pronounced asymmetric contrast is visible in out-of-focus Lorentz images of ilmenite lamellae in hematite. The likelihood that lamellar magnetism may be responsible for this contrast is assessed using simulations that incorporate interfacial magnetic moments on the (001) basal planes of hematite and ilmenite. The simulations suggest qualitatively that the asymmetric contrast is magnetic in origin. However, the magnitude of the experimental contrast is higher than that in the simulations, suggesting that an alternative origin for the observed asymmetry cannot be ruled out. Electron tomography was used to show that the lamellae have lens-like shapes and that (001) planes make up a significant proportion of the interfacial surface that they share with their host.

Key Words: Hematite • ilmenite • lamellar magnetism • Lorentz electron microscopy • electron tomography • transmission electron microscopy






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