Review of methods for the preparation of magnetic metal oxides

Abstract

Metal oxides are a subject of interest because of their optical, electronic, and magnetic properties suitable for a variety of applications. Among the various metal oxides, magnetic metal oxides occupy an important place due to the numerous possibilities of their usage. Until 1740, the only useful permanent magnets known to man were lodestones largely composed of impure magnetite, the black spinel-structure oxide Fe3O4 with a ferrimagnetic arrangement of magnetic moments. The other common rock-forming iron oxide is hematite, the reddish corundum-structure sesquioxide α-Fe2O3, which is antiferromagnetic with magnetization about 200 times weaker than magnetite. The first more serious study of magnetism was made by Gilbert, who published his famous classic book, On the Magnet. But for a long time after that there were no discoveries of any fundamental importance, although many practical improvements in the manufacture of magnets appeared. In 1820 Oersted made the great discovery that an electric current produces a magnetic property, opening the field of electromagnets.