A Research On Ion Substitution And Magnetic Properties Of New-type Strontium Ferrite

As an important kind of magnetic material,Strontium ferrite(SrFe₁₂O₁₉)is widely used as permanent magnet material,magneto optical material,microwave materials,high density magnetic recording materials due to its advantages of high cost-effective,high coercive force,high Curie temperature,good chemical stability and wear-resisting corrosion resistance.The main problem of strontium ferrite material is its unsatisfactory residual magnetism,maximum magnetic energy product and coercivity,which cannot meet the needs of the electronic components increasingly miniaturization and functionalization,thus limiting its large-scale applications.At present,the magnetic properties of strontium ferrite can be optimized by ion substitution,additives,surface coating,etc.Because of its simple operation process,obvious modification effect,non-pollution and other advantages,the ion substitution have become one of the main modification methods of strontium ferrite among them.In this dissertation,aluminum?Al?substituted and lanthanum cobalt aluminum?La-Co-Al?co-substituted strontium ferrite is prepared by sol gel method then tested and characterized by X-ray diffractometer?XRD?,scanning electron microscope?SEM?and vibrating sample magnetometer?VSM?.The influence of Al substitution and La-Co-Al co-substitution on the crystal structure,surface morphology and magnetic energy of strontium ferrite were investigated.The main results are as follows:1.In the Al substituted strontium ferrite SrFe_12-xAl_xO_19,Al³⁺integrated into the lattice well,and the substitution decreased the lattice constant a and c as well as the grain size at certain Al ion contents.The intrinsic coercivity of strontium ferrite was increased by 20.08%but the saturation magnetization and residual magnetic induction intensity decreased by only 9.3%and 7.27%respectively when the Al ion contents x is equal to0.5.2.There was no obvious impurities detected in the La-Co-Al co-substituted strontium ferrite Sr_1-0.75xLa_0.75xFe_11.5-xCo_xAl_0.5O₁₉.Compared with the Al substitution sample SrFe_11.5Al_0.5O₁₉,the substitution of La?Co reduced the lattice constant c of strontium ferrite,while the lattice constant a first decreased and then increased,and the grain size is decreasing in the whole x range.When the x is equal to 0.4 the saturation magnetization of strontium ferrite was increased by 14.23%while the coercive force droped by 6.95%.3.La-Co-Al ion substitution can effectively enhance the various magnetic property of strontium ferrite.When the amount of La,Co,Al substitution is 0.3,0.4,0.5respectively,the saturation magnetization intensity,the intrinsic coercive force,remanence,maximummagneticenergyproductofstrontiumferrite Sr_0.7La_0.3Fe_11.1Co_0.4Al_0.5O₁₉ increased by 3.62%,11.73%,10.80%and 3.62%respectively compared with the pure phase sample SrFe₁₂O₁₉.