Preparation of nanocrystalline barium hexaferrite in a glass medium

doi:10.1016/S0965-9773(97)00222-5

Nanostructured Materials

Volume 8, Issue 6, September 1997, Pages 731-738

Nanostructured Mater...

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Abstract

Barium hexaferrite phase of composition BaO-6Fe₂O₃ of dimensions in the range 8.2 to 17.6 nm have been grown within a glass medium by subjecting the latter to a suitable heat treatment. Magnetization measurements on the resultant glass-ceramic have been carried out at temperatures varying from 20 to 300 K. The coercive field H_c is found to be much smaller than that of bulk hexaferrite. The value of H_c increases as the temperature is reduced. Also, H_c shows an increase with the increase of hexaferrite particle size. It appears that the effective anisotropy constant plays an important role in determining this behavior.

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Cited by (6)

Improvement of the magnetic properties of barium hexaferrite nanopowders using modified co-precipitation method
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Citation Excerpt :
Thus, the preparation of BaFe12O19 powders with high purity, chemical homogeneity, control of structure, fine particle size, narrow particle size distribution and minimum particle agglomeration with high sinter activity has received considerable attention in order to improve the material properties [8]. There are various techniques in order to achieve high quality barium hexaferrite powders such as hydrothermal [8,9], reverse micelle [10], citrate EDTA complexing method [11], glass characterization [12], salt melt technique [13], mechanochemical processing [14,15], sonochemical [16], sol–gel method [17,18], combustion method [19–21], spray pyrolysis technique [22] and co-precipitation method [23,24]. It has been demonstrated that the chemical co-precipitation method is the most suitable technique compared with the other routes due to its low-cost in addition to its suitability for the mass production.
Barium hexaferrite BaFe₁₂O₁₉ powders have been synthesized using the modified co-precipitation method. Modification was performed via the ultrasonication of the precipitated precursors at room temperature for 1 h and the additions of the 2% KNO₃, surface active agents and oxalic acid. The results revealed that single phase magnetic barium hexaferrite was formed at a low annealing temperature of 800 °C for 2 h with the Fe³⁺/Ba²⁺ molar ratio 8. The microstructure of the powders appeared as a homogeneous hexagonal platelet-like structure using 2% KNO₃ as the crystal modifier. A saturation magnetization (60.4 emu/g) was achieved for the BaFe₁₂O₁₉ phase formed at 1000 °C for 2 h with Fe³⁺/Ba²⁺ molar ratio 8 using 5 M NaOH solution at pH 10 in the presence of 2% KNO₃. Moreover, the saturation magnetization was 52.2 emu/g for the precipitated precursor at Fe³⁺/Ba²⁺ molar ratio 12 in was achieved for the precipitated precursor ultrasonicated for 1 h and then annealed at 1200 °C for 2 h. Coercivities from 956.9 to 4558 Oe were obtained at different synthesis conditions.
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Quasi-single magnetic domain M-type barium hexaferrite powders have been synthesized via sol–gel auto-combustion route, followed by secondary heating treatment at 800 °C for 4 h, using barium nitrate, ferrite nitrate, ammonium nitrate, citric acid, and ammonia solution as the starting materials. The auto-combustion producing powders were γ-Fe₂O₃ and BaCO₃ with aid of additional ammonium nitrate to increase the combustion temperature. The influences of the citric acid to metal ions (CA/M) and pH values on the gel auto-combustion, the phase compositions of the synthesized powders and their magnetic properties have been studied. The results showed that the chelation of barium and ferrite ions were important for the phase formation of barium hexaferrite: the phase compositions of the synthesized powders changed from a multi-phased mixture to a single phase of M-BaFe₁₂O₁₉ for the gradually complete complexing of barium and iron ions with citrate as the pH values and CA/M increased. The resulting powders demonstrated that various magnetic properties mainly depended on the variation in phase composition, sintering adhesion between grains and grown-up of crystalline sizes. With CA/M = 1.5, pH 7, the synthesized powders had a particle size distribution in the range of 100–200 nm and a saturation magnetization of 58.0 emu/g at 12 kOe.
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Preparation of nanocrystalline barium hexaferrite in a glass medium

Abstract

Applied Physics Letters

Applied Physics Letters

Journal of Applied Physics

Applied Physics Letters

Journal of Applied Physics