High-quality Fe and γ-Fe2O3 magnetic thin films from an epoxide-catalyzed sol-gel process

High-quality amorphous Fe3+ oxide/hydroxide thin films were fabricated through an epoxide-catalyzed sol-gel process in which hexaaquo Fe3+ salts were condensed in an alcoholic medium with propylene oxide. After addition of the propylene oxide, but prior to gelation, the solution was spin-coated onto quartz disks. The Fe3+ oxide/hydroxide films that formed were extremely uniform and homogeneous with a film thickness of similar to 0.1 mu m. Processing of these films under either oxidizing or reducing conditions allows them to be converted into magnetic iron or iron oxide phases. Calcination under an inert atmosphere at 600 degrees C cleanly converts the Fe3+ oxide/hydroxide gel to hematite (alpha-Fe2O3), while reduction of either the Fe3+ gel films directly or the hematite films in a dilute H-2 flow produces metallic iron. The iron films produced from either of these methods are characterized by a distribution of submicrometer particles on the surface. The metallic iron particles can ultimately be converted to well-formed maghemite (gamma-Fe2O3) particles through slow reoxidation. Magnetic susceptibility measurements taken parallel and perpendicular to the surface indicate that both the iron and the maghemite are anisotropic, showing evidence of long-range interactions parallel to the surface.