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

The saturation magnetization Mₛ, the uniaxial anisotropy Kᵤ, the optical absorption α, the Faraday rotation θF, and the Faraday ellipticity ψF of epitaxial garent films of composition Y_3-xBiₓFe₅O₁₂ and Y_3-yPbyFe₅O₁₂ have been investigated for x≤1.7 and y≤0.25. The magnetostriction constants λ₁₀₀,λ₁₁₁ and the cubic anisotropy K₁ were studied on flux-grown crystals for x≤1. The temperature dependence of Mₛ, K₁, Kᵤ, λ₁₀₀, λ₁₁₁, and θF, ψF at 633 nm has been measured in the range 4.2 K≤T≤Tc. The concentration dependence of these properties is linear. In particular, the contribution of the bismuth and lead to the Faraday rotation ΔθFx and ΔθFy at λ=633 nm turned out to be -25 400 and -18 500 deg cm^-1 at $T=4.2$ K and -20 600 and -18 400 deg cm^-1 at $T=295$ K, respectively. The temperature dependence of θF and ψF 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 Kᵤᵍ is discussed in terms of the single-ion theory.