Optical Measurements on Magnetite Single Crystals

Optical transmission and reflectance were measured on natural magnetite single crystals in the spectral range $0.15<~h\nu <~0.75$ eV. These measurements below and above the semiconductor-to-metal transition temperature $T_{\mathrm{v}}$ have shown that, unlike for the vanadium oxides, there is no collapse of the optical gap at the transition. The present results and the existing data on the transport properties of magnetite indicate that different bands contribute to the electric conduction above and below $T_{\mathrm{v}}$.