High Coercivity Maghemite Films by Spray-Pyrolysis

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Abstract
Maghemite films with coercivity of 1200-1300 Oe, saturation magnetization of around 5000 G, and squareness ratio of 0.63-0.66 have been routinely prepared by spray-pyrolysis onto heated substrates of alumina, MgO(100) and Corning 7059 glass from aqueous nitrate solutions containing Fe, Co, and Mn. Composition and reduction-oxidation treatments were found to dominate coercivity. Glancing angle X-ray diffraction showed a single phase maghemite structure. Transmission electron microscope (TEM) studies on detached film material showed that ultrafine equiaxed particles of 40 to 90 nm contribute to high coercivity. Post-annealing was found to enhance coercivity substantially. These films are potential candidates for magnetic recording media.