Influences Of Rare-earth Substitution On The Structure And Magnetic Properties Of M-type Ferrites

M-type permanent ferrite magnetic has wide application in the fields of permanent magnet, microwave, magnetic light, high density magnetic recording medium, etc. for its fascinating characteristics such as uniaxial magnetocrystalline anisotropy, high coercive force, remanence and magnetic energy product, high Curie temperature and good chemical stability. However, it is difficult to further improve magnetic property using tranditional preparatiom process. Recently, in order to obtain high performance M-type ferrtire for wide range application, great efforts are focused on the following strageties:On one hand, by adjusting microscopic structure, single domain and increased sintering density particles can be prepared to increase the coercivity and remanence. On the other hand, Rare earth substitutions in M-type ferrite can be done to enhance the saturation magnetization intensity and Hcj.In the first part, M-type barium ferrites with substitution of Fe3+by rare-earth Gd3+, according to the formula BaGdxFe12-xO19(x=0.3～1.2) and BaO·n[Fe2-0.3/nGdo.3/nO3](n=5.4～6.0), were prepared by the ceramic process. Influences of the substituted amount of Gd3+on the structure and magnetic properties of BaGdxFe12-xO19(x=0.3～1.2) and BaO·n[Fe2-0.3/Gd0.3/nO3](n=5.4～6.0) compounds have systematically been investigated by XRD and VSM. It is found that all the samples present primarily an M-type structure when the substituted amount x is not more than0.3. GdFeO3is detected as the substituted amount x is above0.3. The magnetic properties such as saturation magnetization (Ms) and remanence (Mr) decrease while coercivity (Hc) increase with the increase in Gd3+mole ratio.In the second part, Magnetoplumbite type calcium ferrites were prepared by the ceramic technology. Structure, morphology and magnetic properties of the samples have systematically been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and vibrating-sample magnetometer (VSM). The experimental results showed that, the magnetic properties of calcium ferrites with Ca2+-La3+-Co2+substitution can be significantly improved. The remanence, magnetic induction coercivity, intrinsic coercivity and maximum magnetic energy of calcium ferrites had a significant improvement compared with that of strontium ferrites with substituted by La3+-Co2+. In addition, the residual flux density of the magnet can still keep high even when the sintering magnet is thin and small.