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

The saturation magnetization $M_s$, the uniaxial anisotropy $K_u$, the optical absorption $\alpha$, the Faraday rotation ${\theta }_F$, and the Faraday ellipticity ${\psi }_F$ of epitaxial garent films of composition ${\mathrm{Y}}_{3-x}{\mathrm{Bi}}_x{\mathrm{Fe}}_5{\mathrm{O}}_{12}$ and ${\mathrm{Y}}_{3-y}{\mathrm{Pb}}_y{\mathrm{Fe}}_5{\mathrm{O}}_{12}$ have been investigated for $x\le 1.7$ and $y\le 0.25$. The magnetostriction constants ${\lambda }_{100}$,${\lambda }_{111}$ and the cubic anisotropy $K_1$ were studied on flux-grown crystals for $x\le 1$. The temperature dependence of $M_s$, $K_1$, $K_u$, ${\lambda }_{100}$, ${\lambda }_{111}$, and ${\theta }_F$, ${\psi }_F$ at 633 nm has been measured in the range $4.2 \mathrm{K}\le T\le T_c$. The concentration dependence of these properties is linear. In particular, the contribution of the bismuth and lead to the Faraday rotation $\frac{\Delta {\theta }_F}{x}$ and $\frac{\Delta {\theta }_F}{y}$ at $\lambda =633\mathrm{}$ nm turned out to be -25 400 and -18 500 deg ${\mathrm{cm}}^{-1\mathrm{}}$ at $T=4.2\mathrm{}$ K and -20 600 and -18 400 deg ${\mathrm{cm}}^{-1\mathrm{}}$ at $T=295\mathrm{}$ K, respectively. The temperature dependence of ${\theta }_F$ and ${\psi }_F$ 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.