High-Quality Fe and γ-Fe₂O₃ Magnetic Thin Films from an Epoxide-Catalyzed Sol−Gel Process

High-quality amorphous Fe 3+ oxide/hydroxide thin films were fabricated through an epoxide-catalyzed sol−gel process in which hexaaquo Fe 3+ 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 Fe 3+ oxide/hydroxide films that formed were extremely uniform and homogeneous with a film thickness of ∼0.1 μm. 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 °C cleanly converts the Fe 3+ oxide/hydroxide gel to hematite (α-Fe 2 O 3 ), while reduction of either the Fe 3+ 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 (γ-Fe 2 O 3 ) 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.