Preparation of spinel-type ferrite thin films by the dip-coating process and their magnetic properties

Abstract

Films of spinel-type ferrite, MFe₂O₄ (M=Ni, Co, Mg, Li_0.5Fe_0.5) 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°C for 2 h in air. The film thickness was about 0.8 μm. The saturation magnetization, σ_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°C for 2 h. In particular, the films were shown to have a much largerH _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.