Magneto-optical investigation of spinel ferrite CuFe 2O 4: observation of Jahn–Teller effect in Cu 2+ ion

Abstract

Magneto-optical properties of spinel ferrite CuFe 2O 4 have been investigated in comparison with those of isostructural Fe 3O 4. The Kerr angle and ellipticity of the ferrites were measured by magneto-optic Kerr effect spectroscopy in the 1.5– 5 eV region. It is found that a strong 2.1-eV absorption peak for Fe 3O 4, due to a d–d intervalence charge-transfer (IVCT) transition in the octahedral sites, Fe 2+(t 2g)→Fe 3+(e g), disappears for CuFe 2O 4. It gives an evidence that the octahedral Fe 2+ sites are well substituted by Cu 2+ ions in CuFe 2O 4. Absorption structures at about 2.5, 3.5, and 3.9 eV observed for both CuFe 2O 4 and Fe 3O 4 are assigned to inter-sublattice charge-transfer transitions between the tetrahedral and the octahedral Fe 3+ ions. Two peaks observed at about 4.3 and 4.7 eV for CuFe 2O 4 are interpreted as due to Jahn–Teller-coupled IVCT transitions, Cu 2+(e g)→Fe 3+(t 2g), in the octahedral sites. The structure at about 1.8 eV observed for CuFe 2O 4 is attributable to Jahn–Teller-coupled d–d crystal-field transitions, 2 E g → 2 T 2 g , in the octahedral Cu 2+ ion.