The Faraday Effect of Bismuth Substituted Rare-Earth Iron Garnet

Anomalous Faraday rotations of the following three series of polycrystalline garnets weremeasured; 1) Gd_3-xBi_xFe₅O₁₂, 2) Gd₂Bi₁Fe_5-yGa_yO₁₂ and Gd₂Bi₁Fe_5-yIn_yO₁₂, and 3) Y_2.25Bi_0.75Fe_5-yGa_yO₁₂ and Y_2.25Bi_0.75Fe_5-ySc_yO₁₂. In series 1 and 2, the rotations were measured in the visible region at room tentperature. The rotation of series 1 increased linearly with x up to x=1.4, and the magneto-optical figure of merit reached 23 deg (at 0.56 µm) in Gd₂Bi₁Fe₅O₁₂. It was found in series 2 that the further substitution of Ga for Fe up to y=1.0 slightly decreased the figure of merit. In series 3, the rotations were measured in the near infrared region at a low temperature (8K) and the results were analyzed by using a one-ton model.It was found that two transitions near 3.1 eV and 2.8 eV, which are related to octahedral irons and tetrahedral irons respectively, were responsible for the anomalous rotation. These transitions were tentatively assigned to oxygen-iron charge-transfer transitions.