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 α, the Faraday rotation θ_F, and the Faraday ellipticity ψ_F of epitaxial garent films of composition Y_3-xBi_xFe₅O₁₂ and Y_3-yPb_yFe₅O₁₂ 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 M_s, K₁, K_u, λ₁₀₀, λ₁₁₁, and θ_F, ψ_F at 633 nm has been measured in the range 4.2 K≤T≤T_c. The concentration dependence of these properties is linear. In particular, the contribution of the bismuth and lead to the Faraday rotation Δθ_F/x and Δθ_F/y 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 θ_F and ψ_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.