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Synthesis of Nanocrystalline Barium-Hexaferrite from Nanocrystalline Goethite Using the Hydrothermal Method: Particle Size Evolution and Magnetic Properties

Published online by Cambridge University Press:  10 February 2011

R. L. Penn
Affiliation:
Materials Science Program, University of WI - Madison, Madison, WI, 53706, [email protected]
J. F. Banfield
Affiliation:
Department of Geology and Geophysics, University of WI - Madison, Madison, WI, 53706
J. Voigt
Affiliation:
Ceramic Synthesis and Inorganic Chemistry Department, Sandia National Laboratories, Albuquerque, NM, 87185
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Abstract

To characterize particle size/magnetic property relationships, 9 to 50 nm in diameter barium hexaferrite, BaFe12O19 (BHF), particles were prepared using a new synthesis route. By replacing the conventional 50 to 100 nm particles of goethite with nanocrystalline goethite produced via the microwave anneal method of Knight and Sylva [1], nanocrystalline BHF was synthesized using the hydrothermal method. Evolution of particle size and morphology with respect to concentration and heat treatment time is reported. Hysteresis properties, including coercivity (0.2 – 1.0 kOe), magnetization saturation (0.1 – 33.4 emu/g), and magnetization remanence (0.004 – 22.5 emu/g) are discussed as a function of particle size. The magnetization saturation and remanence of the 7 nm particles is nearly zero, suggesting the superparamagnetic threshold size for BHF is around this size. In addition, the equilibrium morphology of BHF crystals was calculated to be truncated hexagonal prisms which was verified by experiment, and the isoelectric point, pH of 4.1, was measured for 18 nm BHF particles.

Type
Research Article
Copyright
Copyright © Materials Research Society 1997

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