Development of Multi-Cation-Doped M-Type Hexaferrite Permanent Magnets

We report enhanced permanent magnet performance for multi-cation–substituted M-type Sr-hexaferrites (SrM) prepared using conventional ceramic processes. The final cation composition, Sr0.4Ca0.3La0.3Fe10.2Co0.1Mn0.1Si0.05Mg0.05O19, could be derived through stepwise and systematic cation composition designs, processing, and characterization. The hexaferrites sample sintered in the temperature range of 1200–1220 °C showed an enhanced coercivity (HC) of approximately 4.0 kOe and a residual magnetic flux density (Br) of 2.5–2.6 kG. When samples of the same composition were fabricated into anisotropic magnets through a magnetic-field molding process, performance parameters of Br = 4.42 kG, HC = 3.57 kOe, and BHmax = 4.70 M‧G‧Oe were achieved, a significant improvement over Br = 4.21 kG, HC = 3.18 kOe, and BHmax = 4.24 M‧G‧Oe for the non-substituted SrFe12O19 magnet processed under optimized conditions.