Improvement of the coercivity of strontium hexaferrite induced by substitution of Al3+ ions for Fe3+ ions

► In the present manuscript, a series of SrAlxFe12−xO19 (0 ⩽ x ⩽ 4) have been synthesized. ► It is found that the Al3+ substitutes for Fe3+ spinning upward in the SrAlxFe12−xO19. ► The largest coercivity obtained in the SrAl4Fe8O19 sintered at 1000 °C is 17570.7 Oe. ► The coercivity exceeds the Nb2Fe17B (15072 Oe). ► The mechanism of the improvement of the coercivity induced by Al doping is discussed.