Magnetic Properties of Isotropic Ba-Zn-Al-La System W-type Hexagonal Ferrite Magnets

Experiments were carried out to investigate the effects of A1203 and La203 substitution on magnetic properties of isotropic BaO⋅2ZnO⋅8Fe2O3 magnets. The compositions were chosen according to the formula {(BaO)0.091(ZnO)0.182(Fe2O3)0.727}100-X-Y(A12O3)X(La2O3)Y where X was varied between 0 and 5, and Y between 0 and 4. The raw materials used in this experiment were α-Fe203, BaCO3, ZnO, A12O3 and La2O3 powders. Mixed powders of the raw materials prepared by the wet-mixing method were semisintered at 1200-1400°C in air for 1 h. The resulting products were finely ground by a vibration-mill crusher, compacted into cylindrical specimens, and then sintered at 1225-1350°C in air for 0.5 h. The magnetic properties of {(BaO)0.091(ZnO)0.182(Fe2O3)0.727}100-X-Y(Al2O3)X(La2O3)Y magnets were apparently improved by the substitution of A1203 and La203 for BaO⋅2ZnO⋅8Fe2O3 compound. Some properties of a typical specimen are as follows. The preparation condition: composition {(Ba0)0.091(ZnO)0.182(Fe203)0.727}94(A1203)4(La2O3)2, semisintering condition 1300°C×1 h in air, sintering condition 1300°C×0.5h in air. Magnetic and physical properties: Jm=0.373 T, Jr=0.250 T, Hcj=104.8kA/m, HCB-90.4 kA/m, (BH)max=8.42 kJ/m3, Tc=346°C, D=4.68 Mg/m3, a=5.883×10-10 m, c=32.84×l0-10 m, c/a=5.582.