Optical Properties and Electronic Structures of NiFe$_{2}$O$_{4}$ and CoFe$_{2}$O$_{4}$ Thin Films

We present the growth and investigation of inverse spinel ferrite NiFe$_{2}$O$_{4}$ and CoFe$_{2}$O$_{4}$ thin films. An electron beam deposition system was used to prepare ferrite thin films in the oxygen environment on sapphire and STO single crystal substrates. We measured a variable temperature (80 - 500 K) transmittance of these films to investigate their optical and electronic structures. The optical spectra of thin film samples show insulating characters with several electronic transitions, such as on-site metal $d$ to $d$ and charge transfer oxygen 2$p$ to metal 3$d$ transitions. Electronic transitions have been assigned based on the first principles calculations and comparison with chemically similar Ni and Co-containing compounds.