The relation between magnetic properties and the amount of Al_2O_3 was observed in Al_2O_3-Fe_2O_3-MO system (M=Ba, Sr and Pb), varying the ratio of (Fe_2O_3+ Al_2O_3)/MO from 3.5 to 6.5. In order to obtain a constant and good activity, Fe_2O_3 specially prepared from Fe(CO)_5 Was used. Coercive force of these magnets increased through the addition of Al_2O_3 but saturation or remanent decreased with the amount of Al_2O_3, except at the composition of (Al_2O_3+Fe_2O_3)/BaO<4.5
