Preparation And Magnetic Properties Of CaLaCo-M-type Strontium Ferrite

As one of the most cost-effective and widely-used permanent magnetic materials,M-type hexagonal ferrite?SrM?plays a very important role in the fields of microwave,magnetic-optical and high-density recording due to its cheap raw materials,fine chemical stability and relatively high magnetic properties.In recent years,magnetic materials with higher magnetic properties are required with the advancement of new-energy market,intelligentized office facilities and household appliances.Presently,the ion-substitution and looking for the new preparation method are the two effective ways to improve the magnetic properties of SrM ferrite.In this thesis,CaLaCo-M type permanent ferrites were prepared by the conventional ceramic process,and their phase formation,morphology and magnetic properties were systematically studied.The ways to improve the magnetic properties of CaLaCo-M type ferrites were obtained from the aspects of key preparation technologies,ion-substitution and additives.Firstly,for the single-phase SrM ferrites with a nominal composition of(Sr_0.05La_0.45Ca_0.5)(Fe_0.975Co_0.025)_xO₁₉?x=11.0-8.0?,it was found that the specimen obtained was single-phase when the ratio of atoms??Sr+La+Ca?/?Fe+Co?,S/F?is 1:9.4 and the temperature condition during sintering is 1300oC×3h,and the magnetic properties also achieved the optimum.The phase formation and magnetic properties were affected by changing the sintering temperature and holding time.In addition,under a relatively lower sintering temperature,the single-phase CaLaCo-M type ferrites can be formed only when the holding time is larger than a certain value.Secondly,the substitution of Al or Co ions for Fe ions in(Sr_0.05Ca_0.5La_0.45)(Fe_0.975Co_0.025)_9.4O₁₉9 specimens obtained with S/F=1:9.4 was systematically studied.It was found that the Al-substituted single-phase CaLaCo-M type ferrite can be obtained when the temperature condition is 1300oC×3h during sintering.Nonmagnetic Al ions occupied the sub-lattice sites of Fe in SrM ferrites,and the increasing content of Al ions resulted in the reduction of M_s and the enhancement of H_c.Only when Co ion-substituted is 0.3,CaLaCo-M type ferrites can be formed and the magnetic properties of specimen is optimal.Finally,the substitution of La ion for Sr ion and the additives of SiO₂ in(Sr_0.5-z.5-z La_zCa_0.5)(Fe_0.95Co_0.025Al_0.025)_9.4O₁₉9 specimens obtained with S/F=1:9.4 was studied.It was found that the single-phase SrM ferrites can be obtained when z was between 0.35 and 0.50and the temperature condition was 1200oC×3h.The magnetic properties of La-substituted specimens were affected by changing the arrangement of magnetic atoms.It was also found that the additive of SiO₂ can enhance the intrinsic coercivity(H_cj)of specimens greatly.When the amount of Si in the specimen was 1 wt%,the H_cjj of specimen with a nominal composition of(Sr_0.05La_0.45Ca_0.5)(Fe_0.95Co_0.025Al_0.025)_9.4.4 O₁₉9 can achieve H_cj=337KA/m,which is equivalent of that of the FB9 magnets from TDK company in Japan.