Structure and magnetic properties of a rapidly quenched Zn-Fe-O system

Abstract

Crystal structure and magnetic properties of oxides in a Zn-Fe-O system prepared by the twin-roller quenching method have been examined in order to elucidate the magnetic properties of so called ‘ferromagnetic amorphous oxides’ in a ZnO-Bi 2O 3-Fe 2O 3 system, where ferrimagnetic crystals are precipitated and bring about ferromagnetic properties as revealed by the present authors. Crystalline phases with spinel structure were precipitated in all the specimens with nominal compositions of (100 - x)ZnO · xFe 2O 3 with x = 30 to 90 mol%. The compositional dependence of the lattice constants of these crystalline phases with the spinel structure indicates that the crystalline phases are solid solutions of Fe 3O 4 and ZnFe 2O 4. The specimen with 70ZnO·30Fe 2O 3 composition where ZnFe 2O 4 precipitated shows magnetization of 15.6 emu/g under an external field of 10 kOe, implying that the structure of the ZnFe 2O 4 precipitated in this specimen is different than the normal spinel structure. The magnetization of the as-quenched specimens with 50ZnO·50Fe 2O 3 and 30ZnO·70Fe 2O 3 compositions decreased monotonically with an increase in heat treatment temperature. This change of magnetization is ascribed to the variation of crystal structure during the heat treatment process. Namely, the heat treatment converts the ferrimagnetic ferrites in the Zn-Fe-O system to α-Fe 2O 3 and ZnFe 2O 4 with normal spinel structure. The magnetic properties of the present specimens are applicable to explanation of magnetic properties of ‘ferromagnetic amorphous oxides’ in the ZnO-Bi 2O 3-Fe 2O 3 system.