PREPARATION OF SPINEL-TYPE FERRITE THIN-FILMS BY THE DIP-COATING PROCESS AND THEIR MAGNETIC-PROPERTIES

Films of spinel-type ferrite, MFe2O4 (M = Ni, Co, Mg, Li0.5Fe0.5) have been prepared by a dip-coating method from the sol-gel process. Ferric nitrate, nickel nitrate, cobalt nitrate and lithium nitrate were used as raw materials, and glycerol and formamide were used as solvents. A film was prepared by dipping a silica glass plate. The spinel-type ferrite was obtained by heat-treatment at 700-900-degrees-C for 2 h in air. The film thickness was about 0.8-mu-m. The saturation magnetization, sigma(r), of the film and powder with composition 50NiO.50Fe2O3 was 196 emu CM-3 and 29.1 emu g-1, respectively, and the coercive force, H(c), was 140 and 95 Oe, respectively, after heat-treatment at 800-degrees-C for 2 h. In particular, the films were shown to have a much larger H(c) than the powder. The grain growth of spinel ferrite may be subject to restriction because it is in progress above an amorphous base-plate. The crystals are therefore aligned with the base-plate and have uniaxial anisotropy.