Growth-induced birefringence of Bi-substituted iron garnet films.

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Abstract
Epitaxially grown bismuth-substituted iron garnet films with a composition of Y3-xBixFe5-yMyO12 (M=Ga, Al) have been investigated for Bi-induced changes of the growth-induced birefringence ΔnfG and related properties such as the saturation magnetization Ms, the growth-induced KuG, the Faraday rotation θF and the refractive index nf. The optical properties have been measured by the guided-wave optics technique using a He-Ne 1.15 μm laser. The film birefringence has been determined from the phase mismatch between TE and TM modes obtained from the mode conversion efficiency. KuG, θF and nf depend on the contents of both Bi3+ and nonmagnetic Ga3+ or Al3+, while ΔnfG depends greatly on the content of Bi3+. The Bi concentration dependence of ΔnfG is consistent with the form ΔnfG(x) = ΔnfG(0)(x−x0)(3−x0−x) described for the case of KuG. The results suggest that the ΔnfG can be ascribed to the changes of the electronic structure and local symmetry of the neighbouring oxygen and iron ions induced by the preferential ordering of the Bi3+ ions on dodecahedral sites.