| Because of its high uniaxial magnetocrystalline anisotropy,medium saturation magnetization,great coercivity,good chemical stability,large mechanical hardness as well as favorable performance/price ratio,M-type hexagonal Strontium ferrite has been well established as a permanent magnetic material,but also intensively investigated as high-density perpendicular of magnetic recording media.There are some work which is mainly focused on the Strontium ferrite powder in this paper.1.The LaCo substituted Strontium ferrite powder with smooth surface,hexagonal plate shape were obtain by means of the methods of chemical co-precipitation and synthesis from melts.The average particle size is 200 nm and the typical value of the magnetic properties is ?16=52.0?59.0emu/g,Hc=3360?4990Oe.2.The influence of the different molten salt to the magnetic properties of the Strontium ferrite powder during the prifiring process were investigated which indicated that:The magnetic powder with small size,regular,hexagonal plate shape can be obtain at low temperature or the magnetic powder with high saturation magnetization,great coercivity and regularly hexagonal plate shape will be obtain at medium or high temperature when the molten salt is different.3.Al-substituted Sr-ferrite powder were prepared by oxalate precursor method,the magnetic powder with high coercivity was obtain,the study indicated that:when the raw materials is metal chloride,it is hard to control the precipitation conditions,the components of the precipitation material tend to deviate from the original formula,so the oxalate precipitation method with metal chloride may not be suitable for preparation of M-type Sr-ferrite.4.The iron content,heat preservation time on the effect of SrM properties were systematically researched,which showed that we can get the high coercivity,small particle size,narrow particle size distribution and the columnar particle by increasing the content of iron and extending the heat preservation time at the low temperature.By increasing of the iron content,the ferrite particles have the growth trend along the C axis.Extending the heat preservation time will make the original smaller particles to grow larger and the original larger particles not to grow,finally the particles with uniform size and narrow particles size distribution will be obtain,but the formation of the M phase should be reach the minimum limit temperature,below this temperature,however extend the heat preservation time,the M phase compounds could not be obtain.5.Al substituted Sr-ferrite in the form of SrAIxFc2n-xO19were prepared by the ceramic technology.when n=5.5,the amount of substitution X is in the range of 0?2,the magnetocrystalline anisotropy field and the coercivity increase gradually while the lattice parameter a,c and the ?16 decreased gradually with the increasing of X,when X=1.5,the iron content n is in the range of 5.4?5.8,the Hc=8650±150 Oe,the ?16=40±1 emu/g,while the size and the morphology of the sample remained unchanged,so the increasing of the coercivity when Al substituted Sr-ferrite was mainly caused by the magnctocrystalline anisotropy rather than the grain refining.When the iron content n=5.5,the substitution X=1.5,and the prefiring condition is 1115?×3h,a coercivity as high as 9.9 kOe was measured while the ?16 is 31.0 emu/g. |
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