Direct Observation of Chemical Conversion from Fe3O4 to ε-Fe2O3 by a Nanosize Wet Process

Abstract

e-iron oxide (e-Fe2O3) has drawn attention from the viewpoints of high-density magnetic recording and high-frequency millimeter wave absorption. To date, chemical conversion from Fe3O4 (magnetite) to e-Fe2O3 under wet process conditions have been difficult. Herein, we report that e-Fe2O3 could be obtained from Fe3O4 using a nanosize wet process. In the present method, 10 or 16 nm sized Fe3O4 nanocrystals are used as the precursor. Fe3O4 nanocrystals are embedded in a silica matrix and subsequently sintered around 1000 °C in air, resulting in the chemical conversion from Fe3O4 to e-Fe2O3 being confirmed. In the case of 10 nm sized Fe3O4 precursors, the sample consists of 16% e-Fe2O3 and 84% γ-Fe2O3, whereas in the case of 16 nm sized Fe3O4 precursors, the sample consists of 24% e-Fe2O3 and 76% γ-Fe2O3. The magnetic hysteresis loops of the samples are theoretically predicted using the large hysteresis loop of e-Fe2O3 and the magnetization curve of super-paramagnetic γ-Fe2O3. The experimental and predicted h...