Effect of Heat Treatment on the Magnetic Properties of Zinc Ferrite Thin Film Prepared by a Sputtering Method
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The effect of heat-treatment temperature on magnetic properties of zinc ferrite (ZnFe2O4) thin film deposited on a SiO2 glass at a substrate temperature of 200°C using a sputtering method has been investigated. As-deposited thin film exhibits high magnetization even at room temperature as we reported previously. It is considered that the high magnetization is caused by the random distribution of cations in the ZnFe2O4 nanocrystalline structure, where Fe3+ ions occupy not only tetrahedral (A) but also octahedral (B) sites, and are magnetically coupled by way of the strong superexchange interactions among A and B sites. X-ray diffraction analysis indicates that the as-deposited specimen and those heat-treated at 250 to 900°C for 3 h in air are composed of a single phase of spinel-type ferrite. The crystallite size evaluated by the Scherrer's equation increases from 5 to 20 nm with an increase in the heat-treatment temperature. On the other hand, the magnetization under a magnetic field of 1 T at room temperature increases, takes a maximum of 37 emu/g at 300°C, and then decreases as the heat-treatment temperature is increased. We propose that the increase in the magnetization is ascribed to the grain growth of the ferrimagnetic ZnFe2O4 nanocrystals and the increase of crystallinity, which is explained in terms of densification, or the reduction of the distance between Fe3+ and O2- ions. The decrease in the magnetization above 300°C occurs as a result of the conversion of ZnFe2O4 with the random distribution of cations to that with normal spinel structure.
- 公益社団法人 日本セラミックス協会の論文
公益社団法人 日本セラミックス協会 | 論文
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