STRUCTURE AND HIGH MAGNETIZATION OF RAPIDLY QUENCHED ZINC FERRITE

Abstract

Rapidly quenched zinc iron oxides with nominal compositions of xZnO·(100−x)Fe 2O 3 where x=50, 55, 60, 65 and 70 (mol%) were prepared by using a twin-roller quenching method. X-ray diffraction analyses indicate that the most predominant phases precipitated in all the as-quenched specimens are zinc ferrites with spinel structure. The lattice parameters of rapidly quenched zinc ferrites are slightly smaller than that of normal spinel ZnFe 2O 4. The magnetization of as-quenched 60ZnO·40Fe 2O 3 is 23.8 emu g −1 at room temperature when the external magnetic field is 10 kOe. This value is much higher than the magnetization of ZnFe 2O 4 prepared by the solid state reaction. We suggest that some of the Fe 3+ ions occupy tetrahedral sites as well as octahedral sites. Some of Zn 2+ ions also occupy octahedral sites in the present rapidly quenched zinc ferrites. This leads to the high magnetization caused by strong superexchange interaction between octahedral and tetrahedral Fe 3+ ions, as proposed for ultrafine particles of ZnFe 2O 4 which show high magnetization even at room temperature. Zn K-edge extended X-ray absorption fine structure (EXAFS) measurements support that there exist six-coordinated Zn 2+ ions in the present rapidly quenched zinc ferrites. In addition, a solid solution of magnetite which is suggested by the lattice parameters of as-quenched specimens contributes to the high magnetization as well.