Preparation And Studies Of Magnetic Properties Of High-performance M-type Ferrite Powder

Because of its favorable performance/price ratio, great coercivty, high saturation magnetization, high uniaxial magnetocrystalline anisotropy, high mechanical wear resistance and perfect chemical stability, M-type hexagonal Strontium ferrite is one of the most important magnetic materials used for permanent magnets and it is an important functional materials.In this dissertation, La-Zn and La-Co substituted M-type Strontium ferrite particles were prepared by ceramic processing and molten salt method. The raw material ratio was decided by the formula of LaxSr1-xZnxFe2n-xO19 and LaxSr1-xCoyFe2n-yO19. The magnetic properties, crystal structure and morphology were characterized by vibrating sample magnetometer (VSM), X-ray diffraction (XRD), field emission scanning electron microscopy (SEM), respectively. The influence of calcining temperature and the volume of substitution on magnetic peoperties and crystal structure were discussed. Moreover, the factors which have influence on magnetic properties of Sr-ferrite particles were analysed. The mian conclusions are as follows:1.For La-Zn substituted Strontium ferrite particles, when the amount of substitution x is in the range of 0～0.35, the saturation magnetizationσ16 increases while the coervicity HcJ decreses monotonously. When the amount of substitution x= 0.35 and calcining conditions is 1200℃·1 h, the saturation magnetizationσ16 has the maximum value of 67.75 emu·g-1.2.For La-Co substituted Strontium ferrite particles, when the amount of substitution x is in the range of 0～0.3, the coercivity Hcj increses monotonously while saturation magnetizationσ16 almostly maintains. When the amount of substitution x=0.3 and calcining conditions is 1180℃·1 h, the coercivity HcJ has the maximum value of 5270 Oe.3.In order to prevent the effect of loss of Sr2+ ions on the magnetic properties, appropriate Fe2O3/SrCO3 molar ratio should be selected according to different thchnics.4.The particles size and the morphology of ferrite powder can be controlled by changing the combination of salts. Submicron sized ferrite particles with excellent magnetic properties can be prepared by using NaCl and K2SO4 salts. The aspect ratio of the ferrite particles are very small and the shape is like cube. So, this ferrite particles are suitable for fabricating sintered magnets with high coercivity. By using the combination of salts:KCl, BaCl2 and NaBO2·4H2O or KCl and NaCl, it is easier to fabricate the ferrite powder with hexagonal plate-like shape. This ferrite powder is suitable for preparing flexible bonded magnets.5.With the increasing of the molten salt percent, the saturation magnetizationσ16 of the ferrite powder almost maintained while the coercivity HcJ reduced.6.Although the dry milling technics is more economical and security than the wet ethanol milling technics, the coercivity HcJ significantly reduced.7.The saturation magnetizationσ16 of ferrite powder can be enhanced by washing the powder with dilute nitric acid while the coercivity Hcj decreases slightly.