Preparation of polycrystalline bismuth and aluminum substituted yttrium-iron garnet films by repetitive gel coating on glass substrates

Perpendicularly magnetized films of polycrystalline bismuth-and aluminum-substituted yttrium iron garnet were prepared by spin coating a gel on glass substrates. The coated gel was preannealed at temperatures ranging from 300°C to 700°C for 10 minutes and was successively annealed at 700°C for 4 hours in air to form garnet crystals. Thicker garnet films were obtained by repetitive spin coating and the heat treatments stated above. However, magnetic as well as magneto-optical properties of the films were different according to whether preannealing after each coating was done below or above 400°C. This is caused by the formation of carbon-enriched layers on the free surface of each coated gel layer. These interlayers are considered to occur by hydrocarbon decomposition of the solvent and are found to vanish through evacuation of hydrocarbon from the films by preannealing above 400°C.