Structure And Magnetic Property Of Rare Earth Doped M-type Barium Ferrite

M type hexagonal barium ferrite plays an important role in permanent magnet material owning to high coercive force, high saturation magnetization, good magnetocrystalline anisotropy, stable chemical properties and corrosion resistance, excellent price and other characteristic. Therefore, M type barium ferrite has become an important functional material. As a basic functional material, permanent magnet material has penetrated into various fields of production and life, such as automobiles, motorcycles, televisions, stereos, computers, communications, medical equipment and other aspects. The automobile and motorcycle industry is the largest and the most active market in the application of high grade permanent magnet materials.How to prepare barium ferrite with excellent performance is a hot issue.The barium ferrite that was doped by rare earth ions has excellent performance and it is essential to choose the right rare earth ions. There are a lot of research work about AB12O19 ion replaced has been done, such as using Ca2+, Sr2+, Na+, K+ or rare earth ions substitut Ba2+ ions in A-site, using AI³⁺, Cr³⁺, Ga³⁺ or rare earth ions substitut Fe³⁺ ions in B-site. Because of the special electronic structure, the poor symmetry of the crystal structure,and the magnetic electron in the inner shell, the rare earth elements’electrostatic field interaction and the spin orbit interaction is enhanced, resulting in the high atomic magnetic moments, magnetocrystalline the anisotropy and magnetostriction coefficient, and the complex magnetic ordering structure, the low Curie temperature. Rare earth elements doped in many materials can make the physical properties,chemical properties and mechanical properties of materials improved.The materials doped by rare earth ion,Ba2+, is more superior than that doped by alkali metal. In this paper, nano barium ferrite powders were obtained by the sol-gel auto-combustion method, Gd³⁺ ions, La³⁺ ions and Nd³⁺ ions was selected to dope modification research. Structures and magnetic properties of all samples were characterized by X-ray diffraction （XRD）, Fouriertransform infrared spectroscope （FT-IR）, and scanning electron microscopy （SEM）, vibrating sample magnetometer （VSM）.The main research works are as follows:LBaFe₁₂O₁₉ ferrite powders were obtained by the sol-gel auto-combustion method.The experimental results showed that, the Appropriate sintering temperature is 1000℃, sintering time is 3h, the proper molar ratio of citric acid and metal cations is 1:1.2, pH value of the solution is about 7.2. Gd³⁺ ions substituted Ba2+. The results of XRD showed that the samples are magneto-plumbite type ferrite, lattice parameter decreases gradually with Gd³⁺ions concentration increasing, the crystal axis ratio c/a ranges from 3.9374 to 3.9772.The FT-IR analysis showed that in the vicinity of 587cm-1,545cm-1 and 437cm-1, three obvious characteristics of M ferrite appeare, indicating the samples are single phase magnetoplumbite structure. The VSM analysis showed that the specific saturation magnetization the remanence magnetization of samples decreased with Gd³⁺ions concentration increasing,but the coercivity increased with Gd³⁺ ions concentration increasing. The SEM analysis showed that particle sizes were uniform and good dispersion, the particle size increased from 166nm to 180nm with Gd³⁺ ions concentration increasing, and all the samples belong to the nanoparticles.3. La³⁺ ions substituted Ba2+. The results of XRD showed that the samples are magneto-plumbite type ferrite, average crystallite size decreases from 832A to 573A gradually with La³⁺ ions concentration increasing.the crystal axis ratio c/a ranges from 3.9377 to 3.9431. The results of FT-IR analysis showed that in the vicinity of 587cm-1,545cm-1 and 437cm-1, three obvious characteristics of M ferrite appeare, indicating the samples are single phase magnetoplumbite structure. The VSM analysis showed that the specific saturation magnetization and the remanence magnetization of samples decreased with La³⁺ ions concentration increasing,but the coercivity increased with La³⁺ ions concentration increasing. The SEM analysis showed that particle sizes were uniform and good dispersion, the particle size decreased from 166nm to 136nm with La³⁺ ions concentration increasing, and all the samples belong to the nanoparticles.4. Nd³⁺ ions substituted Ba2+. The results of XRD showed that the samples are magneto-plumbite type ferrite, lattice parameter decreases gradually with Nd³⁺ ions concentration increasing, the crystal axis ratio c/a ranges from 3.9374 to 3.9772. The results of FT-IR analysis showed that in the vicinity of 587cm-1,545cm-1 and 437cm-1, three obvious characteristics of M ferrite appeare, indicating the samples are single phase magnetoplumbite structure. The VSM analysis showed that the specific saturation magnetization and the remanence magnetization of samples decreased with Nd³⁺ ions concentration increasing, but the coercivity increased with Nd³⁺ ions concentration increasing. The SEM analysis showed that particle sizes were uniform and good dispersion, the particle size decreased with Nd³⁺ ions concentration increasing, and all the samples belong to the nanoparticles.