Enhancing Magnetic Properties of M-Type Hexaferrite through Multi-element Substitution: An Aluminum-Nickel-SiO₂-CaO Approach

The improvement of magnetic parameters through dopant introduction has opened up new possibilities for tailored applications of M-type hexaferrite materials. This study investigates the effects of Al³⁺ and Ni²⁺ doping on M-type Sr-hexaferrite prepared via sol-gel technique with calcination at 1200 °C for 4 hrs. The x-ray diffraction analysis confirms the presence of high-purity hexaferrite without any secondary phases. The results highlight the significant impact of Al³⁺ doping on coercivity, leading to an increase from 4500 Oe to 10490 Oe in SrFe₁₂O₁₉ to SrAl₂Fe₁₀O₁₉. The concentration of 1% wt. of SiO₂ and CaO increases the remanence from 65.16  to 67.05 emu/g. The incorporation of Ni²⁺ via doping leads to a notable enhancement in magnetic permeability from 1.75 in SrFe₁₂O₁₉ to 2.75 in SrNi_0.5 Fe_11.5O₁₉, coupled with minimal losses. Two techniques are used to analyze the magnetic permeability of samples: one with vector network analyzer (VNA), and the other with vibrating sample magnetometer (VSM). The values of magnetic permeability with the addition of various substituted elements exhibited the same upward and downward pattern for both approaches. These findings provide valuable insights for optimizing the magnetic performance of M-type hexaferrites.