Faraday Rotation in YIG and TbIG

Measurements of the Faraday rotation in $\mathrm{YIG}$ and $\mathrm{TbIG}$ have been made as a function of temperature in the range 100°–450°K at the helium‐neon laser wavelength of 1.15 μ. This wavelength lies on the edge of the $\mathrm{YIG}$ window at the short‐wavelength absorption limit. Measurements were made on single‐crystal blocks of $\mathrm{YIG}$ and $\mathrm{TbIG}$ up to 7 mm thick in applied fields of up to 10 kOe. In $\mathrm{YIG}$ the major contribution to the Faraday rotation at this wavelength is the dispersive part associated with absorption bands in the visible and near ir. This contribution reaches a maximum of 188°/cm at 280°K and can be fitted to the sublattice magnetization data of Anderson. For $\mathrm{TbIG}$ we find ${\alpha }_F\text{\hspace{0.17em}=\hspace{0.17em}448°/}\mathrm{cm}$ at 300°K and a very strong temperature dependence. In addition we observe a field‐dependent Faraday rotation of −3.8°/cm/kOe at 300°K. Extrapolation of the observed rotations to zero internal field removes he discontinuity in ${\mathrm{|\hspace{0.17em}\alpha }}_F\mathrm{\hspace{0.17em}|}$ which otherwise appears at the compensation temperature (245°K). The zero‐field Faraday rotation may be analyzed in terms of three contributions: a nondispersive part arising from the exchange resonance, a dispersive part arising from the Fe³⁺ sublattices, and a dispersive contribution from the Tb³⁺ sublattice. Additional information on the Tb³⁺ contribution was obtained from Verdet constant measurements on $\mathrm{TbGaG}$ and $\mathrm{TbAlG}$ .