Optimization of Ca–Al–Mn–Si Substitution Level for Enhanced Magnetic Properties of M-Type Sr-Hexaferrites for Permanent Magnet Application

Enhanced hard magnetic properties were achieved in M-type hexaferrite by optimizing the substitution levels of Mn, Al, and Si for Fe, and Ca for Sr within SrFe12O19. The addition of Al–Si–Mn effectively controlled crystallite growth, resulting in an increased coercivity (HC), while causing a decrease in the remanent magnetization (4πMr). A higher Ca content exhibited a trend of increasing the sintered density but decreasing the 4πMr and HC. The optimized composition, considering both the 4πMr and HC, was determined to be Sr0.8Ca0.2Fe10.2Mn0.1Al0.2Si0.1O19−d, with a sintered density of 4.84 g/cm3, 4πMr = 2.22 kG, and HC = 5.10 kOe. This result demonstrates the achievement of isotropic magnets with controlled crystal growth and densification without additional sintering additives. This development is promising, as this enhancement could be achieved without the use of cobalt, an expensive but essential ingredient in high-performance permanent magnets.