Magneto-optical properties of gallium-substituted yttrium iron garnets

Abstract

The optical absorption $\ensuremath{\alpha}$, the Faraday rotation ${\ensuremath{\theta}}_{F}$, and the Faraday ellipticity ${\ensuremath{\psi}}_{F}$ of epitaxial and flux-grown garnets of composition ${{\mathrm{Y}}_{3}}[{\mathrm{Fe}}_{2\ensuremath{-}x}{\mathrm{Ga}}_{x}]({\mathrm{Fe}}_{3\ensuremath{-}y}{\mathrm{Ga}}_{y}){\mathrm{O}}_{12}$ with $0\ensuremath{\le}x+y\ensuremath{\le}2.95$ have been investigated. The wavelength dependence of $\ensuremath{\alpha}$ and ${\ensuremath{\theta}}_{F}$ was studied in the range $500l\ensuremath{\lambda}l1100$ nm at $T=295$ 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 ${\ensuremath{\theta}}_{F}$ and $|{\ensuremath{\psi}}_{F}|$ exhibits a maximum depending on temperature. Both quantities approximately approach zero at $x+y\ensuremath{\approx}3$. The temperature dependence of ${\ensuremath{\theta}}_{F}$ and ${\ensuremath{\psi}}_{F}$ was measured in the range $4.2\mathrm{K}\ensuremath{\le}T\ensuremath{\le}{T}_{C}$ at $\ensuremath{\lambda}=633$ 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.