A compounded rare-earth iron garnet single crystal exhibiting stable Faraday rotation against wavelength and temperature variation in the 1.55 μm band

The Bi, Tb and Yb partially substituted iron garnet bulk single crystals of Tb_3−x−yYb_yBi_xFe₅O₁₂ were grown by using Bi₂O₃/B₂O₃ as flux and accelerated crucible rotation technique for single-crystal growth. Faraday rotation (FR) spectra showed that the specific FR of the (Tb_0.91Yb_1.38Bi_0.71)Fe₅O₁₂ crystal under magnetic field at saturation was measured to be about −1617°/cm at λ=1.55 μm, Faraday rotation wavelength coefficient (FWC, 0.009%/nm) in the wavelength range of 1.50–1.62 μm and Faraday rotation temperature coefficient (FTC, 3.92×10⁻⁵/K) at λ=1.55 μm were even smaller than that of YIG. It is proven that through combining two types of Bi-substituted rare-earth iron garnets with opposite FWC and FTC signs, the compound rare-earth iron garnets with low FWC and FTC may be obtained due to the compensation effect. The saturation magnetization of (Tb_0.91Yb_1.38Bi_0.71) Fe₅O₁₂ crystal is 0.48×10⁶ A/M and is also much smaller than that of YIG. We have found empirically that there is a simple relationship between the FR θ_f(x) and Bi content x for Tb_3−x−yYb_yBi_xFe₅O₁₂, which is given by θ_f(x)=(−2759x+400)°/cm.