Effect of Heat Treatment on the Magnetic Properties of Zinc Ferrite Thin Film  Prepared by a Sputtering Method

NAKASHIMA Seisuke, FUJITA Koji, TANAKA Katsuhisa, HIRAO Kazuyuki

doi:10.14852/jcersjsuppl.112.0.s961.0

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 O^2- 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.

Effect of Heat Treatment on the Magnetic Properties of Zinc Ferrite Thin Film Prepared by a Sputtering Method

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