Highly bismuth-substituted films of yttrium iron garnet were epitaxially grown during deposition for the first time by reactive ion beam sputter-deposition method. It was revealed that substrate temperature and oxygen partial pressure were the key parameters for the epitaxial growth during deposition. Epitaxial growth was observed in the films deposited from the same composition of target onto different substrates of single-crystal garnets with lattice constant ranging from 12.383 to 12.509 Å.

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  Ca-substituted polycrystalline garnets with low optical absorption coefficient, below 2 cm^-1, can be reproducibly prepared by reducing the cause of dispersion and absorption. The lowest optical absorption coefficient which has been measured so far is 0.5 cm^-1 at the wavelength of 1.55 μm. Reduction of porosity can be accomplished by simultaneous substitution of Y³⁺ ions by Ca²⁺ ions in combination with V⁵⁺ ions for charge compensation and by sintering near the temperature at which the anomalous grain growth originates. Also, heat treatment at the temperature in the normal grain growth region reduces optical absorption of CaV-substituted polycrystalline garnets. It was found that the dispersion effect on optical absorption caused by grains is small in comparison with the dispersion caused by pores.

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  Some grains grow anomalously in polycrystalline garnets at elevated temperatures and become larger in size. A method for growing single crystals only through a solid phase reaction by using anomalous grain growth is investigated. This anomalous grain growth technique is successfully applied and the range of growth conditions is established. It is demonstrated that this technique can provide large single crystals (15mm in diameter and 4mm thick) of calcium vanadium substituted YIG with good optical and magneto-optical quality with an optical absorption coefficient,0.4 1/cm and with Faraday rotation, 169 deg/cm at 1.55μm.

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  Single crystals of gadolinium yttrium iron garnet (GYIG) have been grown by the travelling-solvent floating-zone (TSFZ) method with Fe₂O₃ as the solvent. The zone materials consist of 80% Fe₂O₃ and 20% Gd₂O₃-Y₂O₃ mixture. The crystal of approximately 7 x 40 mm in size is obtained.

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  Growth and Magneto-optic characteristics and their dependence on growth conditions of Co-substituted LPE YIG films were reported. The magneto-optical properties depend strongly upon the valence states and content of cobalt ions. Faraday rotation variations versus wavelength have been investigated in the 0.5-1.5 μm range. At 1.5 μm, Co-substituted YIG films give higher rotations (>2000°/cm) than Bi substituted films.

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  A single mode integrated magnetooptical isolator requires a propagating media having the fol-lowing properties: low propagation loss, a thickness within the range of the core diameter of single mode optical fibers and a magnetization in the plane of the guide.
  In the near infrared region (λ = 1.1 μm - 1.6 μm), these requirements can be obtained through the use of gadolinium gallium substituted yttrium iron garnet (YIG) films grown by liquid phase epitaxy. At 1.15 μm, calculations show that a single mode optical isolator is the result of a double substituted structure such as Gd_O.45Y_2.55Ga_0.8Fe_4.2O₁₂/Gd_O.45Y_2.55Ga_O.9Fe_4.1O₁₂/Gd₃Ga₅O₁₂.To master the growth process of these layers, we have investigated the var1at1on of the optical loss of single and double YIG films versus growth rate. The results fit a parabolic curve. SIMS analysis were performed on these substrates and we discovered that (Pb-2Pt) exhibit an important role as decreasing with optical loss.

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  Reducing treatment effects on the optical absorption loss in the near-infrared region were studied for Ca-free and -doped Bi-substituted iron garnet films. (BiGd)₃(FeAlGa)₅O₁₂ films were grown by the conventional LPE technique and annealed in hydrogen (H₂) atmosphere at a step of 50°C between 150 and 400°C for 22 hours. The absorption loss at wavelength λ=0.8μm reached minimum values of 250 ∼ 300 dB/cm by annealing at 250°C for both Ca-free and -doped films. The decrease in the absorption loss at λ=0.8μm by this annealing is mainly ascribed to the reduction of Pb⁴⁺ to Pb²⁺ on the dodecahedral sites in garnets. The wavelength dependence of the difference of absorption loss between as-grown and 250°C-H₂-annealed films has a peak around λ=0.56μm and the difference abruptly decreases in the longer wavelength side. This peak is thought to be due to a charge transfer transition from the crystal field split level of Fe³⁺ to Pb⁴⁺.
  Absorption loss at λ=1.15μm decreased for both Ca-free and -doped films by annealing at 250°C. The values reached ∑2 dB/cm for Ca-doped films and ∼9 dB/cm for Ca-free films. It is thought that the absorption loss of ∼9 dB/cm for the Ca-free films is due to Fe²⁺ which exists at the as-grown state. The increase in the absorption loss by annealing above 250°C may be due to Fe²⁺ ions created by the reduction of Fe³⁺→Fe²⁺.

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  Change of optical absorption after etching was experimentally studied on Ca and Bi doped GdIG films. When argon sputter-etching was performed on as-grown films for a period of time, absorption decreased to the same level as when reduction treatment was performed in Fe(OH)₂ solution. Measurement of lattice constant showed that it increased up to a certain value in both cases of sputter-etching and reducing treatment. Further sputter-etching resulted in the increase of loss, while lattice constant remained unchanged. Change of absorption can be explained by changes in valency of ferric ions, whereas change of lattice constant is mainly attributed to reduction of Pb⁴⁺ to Pb²⁺.

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