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Magnetic Behavior of Nanocomposites Prepared in a Vitreous Alumina Gel

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Abstract

Homogeneous gelled composites of iron and vitreous alumina containing 10-40% Fe have been prepared by room temperature polymerization of aqueous aluminum alkoxide solutions containing ferric nitrate and nitric acid at low pH. Scanning electron microscopy, x-ray diffraction, and Mossbauer spectroscopy demonstrated that this bulk material is comprised of nanometer-sized regions of iron compounds embedded in a vitreous alumina gel matrix. Magnetization data showed that in the as-cured condition these nanocomposites are paramagnetic at room temperature and become either superparamagnetic or ferromagnetic on cooling to 10 K. The magnetic susceptibility increased with the Fe content and with decreasing temperature. Analysis of the temperature dependence of the magnetic susceptibility indicated the magnetic moment per Fe atom was 1.87 μB for the 10% Fe nanocomposite and that it increased linearly with composition to 1.96 μB for the 40% Fe material. Mössbauer effect data showed that subsequent treatment of these materials in a gaseous environment of hydrogen at elevated temperatures (T<400 C) changed the form of the iron in the magnetic regions. These results are compared to that observed for similar nanocomposites prepared using a silica gel matrix.

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Authors and Affiliations

  1. Materials Science and Engineering Laboratory, National Institute of Standards and Technology, Gaithersburg, MD, 20899, USA

    R. D. Shull, J. J. Ritter, A. J. Shapiro, L. J. Swartzendruber & L. H. Bennett

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  1. R. D. Shull
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  2. J. J. Ritter
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  3. A. J. Shapiro
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  4. L. J. Swartzendruber
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  5. L. H. Bennett
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Shull, R.D., Ritter, J.J., Shapiro, A.J. et al. Magnetic Behavior of Nanocomposites Prepared in a Vitreous Alumina Gel. MRS Online Proceedings Library 206, 455–460 (1990). https://doi.org/10.1557/PROC-206-455

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  • DOI: https://doi.org/10.1557/PROC-206-455

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