Investigation of the Origin of the Anomalous Faraday Rotation ofBixCa3−xFe3.5+0.5xV1.5−0.5xO12by Means of the Magneto-optical Kerr Effect

The polar magneto-optic Kerr effect of ${\mathrm{Bi}}_{0.8}$ ${\mathrm{Ca}}_{2.2}$ ${\mathrm{Fe}}_{3.9}$ ${\mathrm{V}}_{1.1}$ ${\mathrm{O}}_{12}$ has been measured between 0.5 and 0.24 μm. A strong magneto-optical transition is found at 0.47 μm which is not observed in ${\mathrm{Y}}_3$ ${\mathrm{Fe}}_5$ ${\mathrm{O}}_{12}$. This transition is concluded to be the origin of the anomalous large Faraday rotation of ${\mathrm{Bi}}_x{\mathrm{Ca}}_{3-x}{\mathrm{Fe}}_{3.5+0.5x}{\mathrm{V}}_{1.5-0.5x}{\mathrm{O}}_{12}$ recently reported and is interpreted as a charge transfer of an electron from an oxygen $p$ orbital to an antibonding $e$ orbital of the tetrahedral iron complex. The large rotation is attributed to a mixing of O and Bi orbitals.