Abstract
In copper iron oxide (CuFe2O4: Cu-ferrite), two-fold degeneracy of the dγ level of the Cu2+ ions on the octahedral site which is the Jahn-Teller center is lifted owing to the Jahn-Teller distortion below 360°C and has the degeneracy above 360°C To investigte the dγ level, the valence band of Cu-ferrite was analyzed by means of X-ray photoelectron spectroscopy (XPS). The dγ signal of XPS appeared at a shoulder on the low-energy side in the 3d orbital below 360°C and disappeared above 360°C From the width of the dγ signal, the Jahn-Teller energy was estimated to be about 0.3-0.4 eV. The properties of the magnetization and electric conductivity of Cu-ferrite changed according to the state of the dγ level.
