Effect of Fe3+/Fe2+ Ratio on Superparamagnetic Behavior of Spin Coated Iron Oxide Thin Films

Iron oxide thin films exhibit structural and magnetic properties that are different from their bulk counterpart. Iron oxide (especially magnetite and maghemite) is one of the most commonly used magnetic materials due to high saturation magnetization M_s, and high magnetic susceptibility that makes it a potential candidate for spintronic applications. Iron oxide thin films, with variation in the ratio of Fe³⁺ to Fe²⁺ cations, are prepared using sol-gel and spin coating method. The ratio of Fe³⁺/Fe²⁺ is varied as 1, 1.25, 1.5, 1.75, and 2. For comparative purposes, iron oxide thin films are also prepared using Fe³⁺ and Fe²⁺ cation, separately. Use of Fe³⁺ cations results in the formation of hematite phase of iron oxide along with maghemite while Fe²⁺ cations are responsible for the formation of maghemite phase. Varying Fe³⁺/Fe²⁺ ratio as 1, 1.25, 1.5, and 1.75 gives maghemite phase, whereas Fe³⁺/Fe²⁺ ratio of 2 results in the formation of magnetite phase. Thin films prepared with Fe²⁺ cations show ferrimagnetic behavior while a transition to superparamagnetic behavior is observed with variation in Fe³⁺/Fe²⁺ ratio as 1, 1.25, 1.50, 1.75, and 2.