Preparation And Properties Of Sol-gel Barium Ferrite Thin Films

M-type hexagonal barium ferrite (BaM) are widely applied in magnetic recording and microwave communication, due to its excellent chemical and mechanical stability, low loss, high magnetocrystalline anisotropy and gyromagnetic property. In this paper, Three different sols consisted of Fe(OH)3, citric acid and EDTA respectively were prepared and Sol-gel technology was used to fabricate BaM thin films. Effects of the ratio of Ba2+ to Fe3+, the type and amount of chelating agent, heat treatment condition on the morphology, the texture, and magnetic properties of BaM thin films were investigated. Our results show that the type of the sols has a significant influence on the morphology and performance of the BaM thin films. Thin films with c-axis texture can be obtained by the three sol systems.BaM thin films can be prepared by the Fe(OH)3 system with the ratio of Ba2+ to Fe3+ equal to 3,5,10.5,11 or 13.5 and the best texture can be acquired when the ratio is 10.5. BaM thin films with textured c-axis can be fabricated when the thin films were treated at 1000℃for 3 hours. The c-axis of the crystallites of the BaM thin films is normal to the sapphire (00l) substrates and the [110] direction of the film is parallel to the [100] direction of the substrate. The morphology of the film shows mixture of platelet-shaped and stick-shaped crystallites. The films present the magnetocrystalline anisotropy and easy magnetization direction is out-of-plane rather than in-plane. The saturation magnetization out-of-plane increases, while coercivity at first increases and then decreases with increase of annealing temperature. when the thin films were treated at 1000℃from 1 hour to 4 hours, the saturation magnetization can be improved from 282.2 Gs to 328.5 Gs ,however, the coercivity increase from 1459.85 Oe to 4019.6 Oe at first and then decrease to 2900 Oe, reach 1567.3 Oe at last. With the increase of the thickness, the preferential growth with c-axis perpendicular to the film plane was suppressed. The remanence ratio was less 0.4 and the coercivity was close to 4 kOe when the thickness of the thin films reached 1.05μm.The BaM thin films produced by adding citric acid preferred to nucleate with c-axis in plane. The morphology displayed that stick-shaped crystallites covered almost the whole surface of the thin films. The coercivity raised with the increase of the amount of citric acid. The preferential c-axis orientation growth needs higher annealing temperature, and well-textured thin films can be obtained at 1100℃for 3 hours.The prefer sol-system for the BaM thin film is EDTA system, The BaM thin films manufactured by EDTA system had clear facetted crystallites. The morphology of the crystallites indicated that crystallites were highly smooth. High-quality BaM thin films can be obtained when the atomic ratio of iron to barium is between 8 and 10.5. The thin films have regular hexagonal platelet-shaped crystallites and very strong perpendicular magnetic anisotropy after annealing for 2 hours at 1100℃. In the perpendicular direction, the remanence ratio and coercivity reach up to 0.75, 3.4 kOe respectively. The remanence ratio in-plane is about 0.12 and coercivity force is about 1.1 kOe.