Magnetic and magneto-optic properties of lead- and bismuth-substituted yttrium iron garnet films

Abstract

The saturation magnetization ${M}_{s}$, the uniaxial anisotropy ${K}_{u}$, the optical absorption $\ensuremath{\alpha}$, the Faraday rotation ${\ensuremath{\theta}}_{F}$, and the Faraday ellipticity ${\ensuremath{\psi}}_{F}$ of epitaxial garent films of composition ${\mathrm{Y}}_{3\ensuremath{-}x}{\mathrm{Bi}}_{x}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$ and ${\mathrm{Y}}_{3\ensuremath{-}y}{\mathrm{Pb}}_{y}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$ have been investigated for $x\ensuremath{\le}1.7$ and $y\ensuremath{\le}0.25$. The magnetostriction constants ${\ensuremath{\lambda}}_{100}$,${\ensuremath{\lambda}}_{111}$ and the cubic anisotropy ${K}_{1}$ were studied on flux-grown crystals for $x\ensuremath{\le}1$. The temperature dependence of ${M}_{s}$, ${K}_{1}$, ${K}_{u}$, ${\ensuremath{\lambda}}_{100}$, ${\ensuremath{\lambda}}_{111}$, and ${\ensuremath{\theta}}_{F}$, ${\ensuremath{\psi}}_{F}$ at 633 nm has been measured in the range $4.2 \mathrm{K}\ensuremath{\le}T\ensuremath{\le}{T}_{c}$. The concentration dependence of these properties is linear. In particular, the contribution of the bismuth and lead to the Faraday rotation $\frac{\ensuremath{\Delta}{\ensuremath{\theta}}_{F}}{x}$ and $\frac{\ensuremath{\Delta}{\ensuremath{\theta}}_{F}}{y}$ at $\ensuremath{\lambda}=633$ nm turned out to be -25 400 and -18 500 deg ${\mathrm{cm}}^{\ensuremath{-}1}$ at $T=4.2$ K and -20 600 and -18 400 deg ${\mathrm{cm}}^{\ensuremath{-}1}$ at $T=295$ K, respectively. The temperature dependence of ${\ensuremath{\theta}}_{F}$ and ${\ensuremath{\psi}}_{F}$ can be described in terms of the sublattice magnetizations inferred from the fit of the molecular-field theory to the measured saturation magnetization. The extracted magneto-optical coefficients reveal a nonlinear concentration dependence. The magnitude of the growth-induced anisotropy is essentially controlled by the supercooling of the melt for both the lead- and bismuth-substituted films. The temperature dependence of ${K}_{u}^{g}$ is discussed in terms of the single-ion theory.