Amorphous ferrimagnetic oxides in the Fe₃O₄-CaO-SiO₂ system were made by the rapid quenching method and then reduced by accelerated hydrogen. The magnetic properties, crystal phases and the precipitation rate of micro-crystalline irons under a heating process were investigated.
When an amorphous oxide with the magnetization of about 3 emu/g was heated in H₂ gas at 640°C, which is lower than that of the crystallization temperature, the magnetization was enhanced to an approximate value of 7emu/g. The precipitated irons of about 100Å were observed in the sample heated at 550°C.
The change of solid phase in the reducing process was summarised as follows. At first, CaFeSiO₄ phase precipitated in the amorphous matrix at about 600°C, and then the CaFeSiO₄ phase began to decompose into Fe and CaSiO₃ at about 700°C.
The precipitated Fe increased markedly the magnetization of samples. The precipitation rate of the Fe was dependent on the content of CaO and SiO₂. Microcrystalline irons began to precipitated at about 400°C for the sample with a large quantity of CaO, and at 500°C for the sample with much SiO₂.
The precipitation rate of Fe seemed to be not affected by the Fe₃O₄ content. The magnetization of sample sufficiently reduced was about 60 emu/g.