Abstract
AbstractTo 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.
Highlights
The hexagonal ferrites, a group of ferromagnetic oxides, are important because of their high coercive force [2]
The bit size of magnetic recording could be reduced through a compromise between optimizing BHF magnetic properties and reducing particle size
This paper presents a new method of synthesizing nanocrystalline BHF particles using a nanocrystalline goethite precursor via the hydrothermal synthesis route, reports particle size control, and the relationship between particle size and hysteresis properties
Summary
The hexagonal ferrites, a group of ferromagnetic oxides, are important because of their high coercive force [2]. Several examples of the hydrothermal synthesis of BHF exist in the literature a(d [10-171 These syntheses, involving autoclaving of a suspension of goethite or hematite and barium hydroxide, produce BHF particles typically in the micron range. This paper presents a new method of synthesizing nanocrystalline BHF particles using a nanocrystalline goethite precursor via the hydrothermal synthesis route, reports particle size control, and the relationship between particle size and hysteresis properties. Images are produced from the best avabble original document This mixture was allowed to stir for one hour before microwave annealing at high power in a standard microwave for four periods of about 40 seconds with shaking between each period. Suspensions of 0.05 M nano-g and barium hydroxide, adjusted to a pH of 13.1 using sodium hydroxide, were prepared and heat treated at 250°C for two, four, eight, 24, and 48 hours. The pHs were adjusted by adding acetic acid or al PI ammonium hydroxide to the suspensions, and pHs were remeasured after the suspensions were allowed to stand for 24 hours
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