Ultrafine magnetite particles of average diameter 4-7 nm were prepared by precipitation in a poly(vinylalcohol) (PVA) aqueous solution. Crystallinity of the particles decreased with increasing PVA concentration, while the morphology and particle sizes remained almost unchanged. The dispersion of the magnetite particles prepared at 1 wt% PVA was particularly stable. The saturation magnetization of the particles was above 50 emu/g, in spite of their small size and low crystallinity compared with conventionally prepared fine magnetite particles.
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