Synthesis of new amorphous oxides with ferromagnetic character in iron oxide-based systems

New amorphous oxides with ferromagnetic character have been found in the Sr-Fe-O and Bi-Fe-O systems. The compositions were 35SrO⋅65Fe2O3 (mol%) and Bi3Fe5O12, and the specimens were prepared by using the twin-roller quenching method. The ferromagnetic character was ascertained by means of magnetization measurements at room temperature. Although the magnetization tended to saturate at relatively low external fields for both systems, hyperfine structure in the Mössbauer spectra was barely observed at room temperature for Bi3Fe5O12 only. It is thought that this phenomenon is due to the superparamagnetic behavior of microcrystal-like clusters which may exist in these amorphous oxides.