磁性流体からのマグネタイト薄膜の作成とその性質について

概要

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Magnetite thin films of about 0.3 micron thickness were prepared by following procedure. Magnetic fluid, which was composed of magnetite colloid, oleate as dispersing agent and decane as base solvent was spread on polished alumina plates. After the plates were dried, they were put into silica tube and heated at 500°C in CO-CO2 gases mixture so as to decompose the residual solvent and organic surfactant in spread film, keeping the magnetite phase unchanged. Then the plates were separately sintered in an atmosphere of about 10-5 Torr. at various temperatures, in order to controll the grain size of magnetite in the film. The saturation induction of 5 KG, remanent induction of about 3 KG and coercive force of 400 Oe were obtained by selecting the sintering temperature between 650 and 750°C. Aluminum solved into magnetite at higher temperature, resulting in the decrease of saturation induction. According to the observation of microstructure, it seemed that the densification of magnetite him by sintering was not enough, presumably due to the large volume ratio of hydrocarbon (surfactant) to magnetite colloid in spread film. The magnetite thin film obtained here exhibited the increase of coercive force up to 1200 Oe by oxidizing it in an air.
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