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Because of its large uniaxial anisotropy,favorable performance/price ratio,higher Curie temperature and perfect chemical stability,hexagonal Barium-Strontium ferrite with the magnetoplumbite（M） structure（BaM/SrM） is one of the most important magnetic materials used for permanent magnets and magnetic recording media.It is hard to improve their magnetic properties by using conventional process.In recent years,however,it has been recognized that（1） Uniform particle size can be achieved to imprve the fabrication process by a molten salt method,in which a comnibation of different cosolvent was introdued into the process to reduce the sintering temperature;（2） Some intrinsic magnetic properties,such as magnetocrystalline anisotropy field etc,can be improved by substituting Sr/Ba and Fe location in SrM/BaM ferrite.In this thesis,we studied the the influence of different cosolvent and substitution on the microstructure and the magnetic performance of SrM ferrite.Samples were produced by ceramic procedure method.On the one hand,three goups of fluxs（10%of mass ratio of raw material） have been investigated:（1） 5%KCl+5 NaCl;（2） 5%KCl+5%NaCl+2%NaBO2;（3） 10%K2SO4.On the other hand,LaxSr1-xCoxFe2n-xO19 has been studied with n=5.7（based on previous experience） and x=0.2,0.25,and 0.3.1.Investigation of flux on the properties of SrM（1） The synthetizing process of SrM ferrite can be expedited by all of these three fluxs,and the efficiency of them are:NaCl+KCl+NaBO2＞NaCl+KCl＞K2SO4.（2） The investigation showed that the grains can grow along different crystal axis with the different sinting temperature and time.2.Investigation of LaCo substituted SrM（1） With x increasingσ16 decreases;and lowers than when not substituted.According to actual needs can choose a suitable x and Tc.Flux added later,when Tc＜1280℃,with the pre-firing temperature,maintaining the same,but when Tc=1280℃,σ16 decreased.（2） As described in the references,the coercivity of LaCo substituted LaxSr1-xCoxFe2n-xO19 ferrite reached maximum when x=0.25.For added molten salt,when the sintering temperature increases,the coercivity first increases and then decreases.（3） The grain size can gereduced by LaCo substituting. （4） When Tc=1200℃,by LaCo substituted so that no reaction Fe2O3 phase gradually weakened and disappeared,single phase LaxSr1-xCoxFe2n-xO19 ferrite powders were fabricatedIn conclusion,high performance permanent SrM ferrite powders were fabricated,on the one hand,by selecting proper cosolvent,sinting temperature and duration,and on the other hand,also by optimizing the composition of LaCo-substituted SrM ferrite.
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