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-Bi2O3-Fe2O3 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 . x Fe2O3 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 Fe3O4 and ZnFe2O4. The specimen with 70ZnO . 30Fe2O3 composition where ZnFe2O4 precipitated shows magnetization of 15.6 emu/g under an external field of 10 kOe, implying that the structure of the ZnFe2O4 precipitated in this specimen is different than the normal spinel structure. The magnetization of the as-quenched specimens with 50ZnO . 50Fe2O3 and 30ZnO . 70Fe2O3 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 alpha-Fe2O3 and ZnFe2O4 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-Bi2O3-Fe2O3 system.
