Synthesis of phase pure iron oxide polymorphs thin films and their enhanced magnetic properties

摘要

The α-Fe_2O_3 thin film was prepared on liquid-vapor interface at room temperature by a facile and cost effective method, which was converted to Fe_3O_4 and γ-Fe_2O_3 films by reduction and oxidation process. The morphological and structural characterizations reveal the average crystallites size in α-Fe_2O_3, Fe_3O_4 and γ-Fe_2O_3 films 12.8, 9.2 and 19 nm with rms roughness 4.35, 4.60 and 8.21 nm, respectively. From magnetic measurements, the α-Fe_2O_3 thin film shows a room temperature super-paramagnetic behavior with saturation magnetization 18 emu/cm~3, while Fe_3O_4 and γ-Fe_2O_3 thin films exhibit fer-rimagnetic behavior with saturation magnetization values 414.5 and 148 emu/cm~3, respectively. A significantly higher value of saturation magnetization is observed in α-Fe_2O_3 film, which is trusted due to the uncompensated surface spins in the film. The converted Fe_3O_4 film also shows enhanced saturation magnetization due to the reduction in antiphase boundaries, whereas the magnetization in γ-Fe_2O_3 film decreases comparatively. The magnetic property of the γ-Fe_2O_3 is explained on the basis of the Fe~(3+) ions vacancy at the octahedral position in its structure.