The thermal decomposition and crystallization processes of two types of films with various thicknesses prepared by spin-coating aqueous and acetylacetonic solutions made by dissolving metal nitrate hydrates of appropriate ratios for the garnets, are described. It was found that the aqueous films decomposed with endothermic reactions over a broad temperature range from 80-500-degrees-C, while the acetylacetonic films decomposed at two strong exothermic reactions at temperatures of 130-degrees-C and 250-degrees-400-degrees-C. Both films decomposed to become amorphous oxides, which then began to crystallize at a temperature of about 600-degrees-C. It was also found that when the amorphous oxide films were thinner than 0.3 mum, the garnets were formed directly from the amorphous oxides. When the films were thicker than 0.3 mum, intermediate orthoferrites were formed which, upon further heating, transformed to the garnets. Differential thermal analysis, thermogravimetry, and X-ray diffraction data in the temperature range 20-750-degrees-C are given and discussed.