Magneto-optical properties of gallium-substituted yttrium iron garnets

The optical absorption $\alpha$, the Faraday rotation ${\theta }_F$, and the Faraday ellipticity ${\psi }_F$ of epitaxial and flux-grown garnets of composition $\left\{{\mathrm{Y}}_3\right\}\left[{\mathrm{Fe}}_{2-x}{\mathrm{Ga}}_x\right]\left({\mathrm{Fe}}_{3-y}{\mathrm{Ga}}_y\right){\mathrm{O}}_{12}$ with $0\le x+y\le 2.95$ have been investigated. The wavelength dependence of $\alpha$ and ${\theta }_F$ was studied in the range $500<\mathrm{}\lambda <1100\mathrm{}$ nm at $T=295\mathrm{}$ K, revealing a strong reduction with increasing gallium content except for wavelengths between 600 and 700 nm. In this range the variation on $x+y$ for both ${\theta }_F$ and $\left|{\psi }_F\right|$ exhibits a maximum depending on temperature. Both quantities approximately approach zero at $x+y\approx 3$. The temperature dependence of ${\theta }_F$ and ${\psi }_F$ was measured in the range $4.2\mathrm{K}\le T\le T_C$ at $\lambda =633\mathrm{}$ nm. It can be described in terms of the sublattice magnetizations which were inferred from the fit of the molecular field theory to the measured saturation magnetization. The magneto-optical coefficients have been determined as a function of the gallium content.