Coercivity of Barium Ferrite Particles with Superparamagnetic Coating

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概要

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• The coercivity mechanism of submicron barium ferrite (BF) particles with a superparamagnetic overcoat (i.e. δ- FeOOH or Fe3O4 fine particles) was investigated by experimental observation and micromagnetics based on the two-component Stoner-Wohlfarth model with interfacial coupling. For overcoating microcrystalline δ- FeOOH, BF particles were first coated with an Fe2+ solution at certain concentrations, followed by the addition of NaOH(aq), and finally oxidized by 35 wt% H2O2(aq). For Fe3O4 coating, BF particles were coated with a mixed solution of Fe3+ and Fe2+ first at certain concentrations, followed by NaOH(aq). The results showed that the coercivity of BF particles decreased greatly while their saturation magnetizations were maintained at high levels. When Fe3O4 nanoparticles were used as the coating material, the saturation magnetization of the coated BF stayed at about the same level as that of the pure BF, 70 emu/g. The analytical calculation was successful in explaining quantitatively the effect of the coating, showing that the amount of coercivity decrement was related well to the uniaxial anisotropy constants of δ- FeOOH or Fe3O4 fine particles on the surface of BF. In addition, the superparamagnetic coating was found to behave ferrimagnetically during magnetization reversal. The larger the volume of coating, the lower the coercivity. Moreover, the weaker exchange coupling between the barium ferrite and δ- FeOOH or Fe3O4 further depresses the coercivity for the coated BF with thicker coatings.

• Publication Office, Japanese Journal of Applied Physics, Faculty of Science, University of Tokyoの論文
• 1997-08-15

著者

• Chin Tsung-shune

  Department Of Materials Science & Engineering Tsing Hua University

• Tung I-chung

  Department Of Materials Science And Engineering National Chiao Tung University

• Yang Jyh-shinn

  Division Of General Education National Taiwan Ocean University

• Tung I-Chung

  Department of Materials Science and Engineering, National Tsing Hua University,

• Chin Tsung-Shune

  Department of Materials Science and Engineering, National Tsing Hua University,

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