Synergistic Enhancement of Coercivity and Dielectric Performance in Al-Sm Co-Doped SrFe₁₂O₁₉ for High-Frequency Applications

Magnetic nanomaterials with tunable dielectric and magnetic properties are essential for high-frequency applications. M-type strontium hexaferrites are widely used; however, their moderate magnetization, high dielectric loss, and limited tunability restrict broader usage. Prior studies employed single-ion doping to enhance individual properties, but often lacked simultaneous optimization of electrical and magnetic behavior. In this work, we introduce a novel Al-Sm co-doping strategy designed to simultaneously overcome these limitations by synergistically modifying dielectric and magnetic responses. The nominal composition SrAl_xSm_xFe_12-2xO₁₉ (x = 0.0-0.8) was synthesized using the sol-gel method and characterized by XRD, SEM, EDX, and FTIR. The electric and magnetic properties were systematically evaluated. Our results show that Al³⁺ effectively reduces dielectric loss and conductivity, while Sm³⁺ enhances magnetic anisotropy and coercivity. An optimal composition at x = 0.2 exhibits high coercivity (6805 Oe) and low dielectric loss, while the sample at x = 0.8 achieves a maximum dielectric constant (∼58) with minimal loss. These findings highlight, for the first time, that Al-Sm co-doping provides a dual improvement in dielectric and magnetic performance, surpassing previously reported single-doping approaches. The optimized compositions demonstrate strong potential for next-generation high-frequency and EMI absorption devices, underscoring the technological relevance of the proposed co-doping strategy.