By ferrite plating which utilizes Fe2+ --> Fe3+ oxidation, polycrystalline films of ferromagnetic spinels (MFe2O4, M = Fe, Co, Ni, Zn, Al, Cr, Ti, etc.) can be synthesized directly from an aqueous solution at 24-100 degrees C. This low temperature process allows us to fabricate new ferrite film devices on substrates of such non-heat-resistant materials as plastics, GaAs integrated circuits, and biomaterials. Applying Ar laser beams during plating greatly enhances the deposition rate of the films (up to approximate to 2 mu m/min), and enables selected-area growth, or patterning, of ferrite film without using a mask. Power ultrasound waves applied to the aqueous solution improves the crystallinity of the ferrite films. Ferrite plating bears a close analogy to the bacterial Fe3O4 (magnetosome) synthesis. Applications of ferrite-plated magnetic oxide films to various kinds of biomedic and magnetic devices are described.