Infrared optical properties of cobalt (II) spinels

Experimental results of optical measurements on cobalt (II) spinel thin films (Co3O4, CoFe2O4, CoMnFeO4) are compared to the infrared lattice vibrational spectra determined by Kramers Kronig analysis and oscillator fit calculations. The ionic character of cobalt (II) spinels is discussed in connection with the TO-LO splitting and found to follow the trend: aluminate and ferrite > chromite > cobaltite. The study of the band ionicity in the series of spinels MFe(2)O(4) and MCr(2)O(4) (M=Co, Ni, Cu and Zn) shows that the TO-LO splitting may be correlated with the classical parameters deduced from the ligand-field and X-ray spectroscopies.