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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 ( \({\rm M_{s}}\) ), 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. [ABSTRACT FROM PUBLISHER]

Bismuth iron oxide (Bi1−xKxFeO3) thin films are prepared using sol-gel and the spin coating method. Films are deposited onto copper substrates and are annealed in the presence of vacuum with 500 Oe magnetic field at 300 °C. Potassium has an ionic radius of 1.64 Å and replaces Bi, which has an ionic radius of 1.17 Å. Based on the ionic radii difference of Bi3+ and K+, the dopant concentration is varied in the range \({ {{{x}} =}}~0.0\) –0.3. X-ray diffractometer analysis shows that at \({{x}} {=} {0.3}\) an impurity phase (K2O) appears, which was not present at low dopant concentrations. It is shown here that ferromagnetic behavior arises in doped BiFeO3 films due to suppression of helical spin structure. In addition, as K+ replaces Bi3+ the charge compensation mechanism gives rise to oxygen vacancies and to the formation of Fe4+ cations, thus inducing ferromagnetic behavior. Variation in dopant concentration strongly affects the dielectric properties. Increase in dielectric constant up to \(\sim 84\) was observed with increase in dopant concentration up to 0.15. Decrease in dielectric constant ( \(\sim 25\) ), beyond 0.15 doping concentration, might have been observed because of the appearance of impurity phase as is observed in structural and magnetic properties. [ABSTRACT FROM PUBLISHER]

The study of on iron oxide, especially magnetite Fe3O4, in the form of thin films and nanostructures, is interesting due to its wide applications in data storage, biomedical, and spintronic devices. Seven different sols are synthesized with varying concentration from 1.8 to 0.6 mM using the sol-gel technique. The concentration of 1.4 mM results in a pure phase whereas others show mixed magnetite and maghemite phases. In addition, changes in film preferred orientation from (400) to (220) planes are responsible for changing the ferromagnetic behavior of films to ferrimagnetic with increased saturation magnetization. Free growth of iron oxide nanostructures, including nanoneedles and nanobrushes, are observed in scanning electron microscope images. [ABSTRACT FROM PUBLISHER]