Optical Properties of Single Crystals of Fe7Se8 and Co7Se8

The optical and magneto-optical properties of single crystals of Fe7Se8 and Co7Se8, grown by the Bridgman technique, have been studied. Spectra of the normal-incidence reflectivity, magneto-optical Kerr effect, and UPS were measured at room temperature. The diagonal and off-diagonal elements of the conductivity spectra obtained from these measurements showed that the difference in magnetic behavior of Fe7Se8 and Co7Se8 is caused by the difference in the 3d electron bandwidth just around the Fermi level. It was also found that the contribution of the spin polarization of conduction electrons to the magneto-optical effect is not significant, but that of a band-to-band transition is more effective. We propose a schematic band structure for Fe7Se8, and tentatively assign the transitions corresponding to the absorption spectra and the magneto-optical spectra.