Ca-Co co-doped strontium ferrite ceramic with tunable magnetic properties for enhanced microwave absorbing application

M-type strontium ferrite (SrFe₁₂O₁₉), due to its excellent thermal stability, corrosion resistance, resistivity, curie temperature, and magnetic anisotropy, should be an ideal candidate for designing microwave absorbers, and the only obstacle is its unsatisfied magnetic properties. Herein, we proposed a co-doping strategy to tune the magnetic properties of SrFe₁₂O₁₉, namely Ca-Co co-substituted SrFe₁₂O₁₉ (Ca_xSr_1-xFe_12-xCo_xO₁₉; x ≤ 0.4), which is fabricated via a solid phase sintering process. By changing the co-doping ratio (x = 0.1, 0.2, 0.3, and 0.4), the magnetic properties were well regulated, including saturation magnetization (41.70∼57.92 emu⋅g ^{− 1}), coercivity (156.507∼291.747 Oe), and magneto-anisotropy constant (1.476∼2.409×10⁶ erg/cm³). As initially expected, the Ca_xSr_1-xFe_12-xCo_xO₁₉ (x = 0.) ceramic show good microwave absorbing performance, for example, an optimal reflection loss of −21.3 dB and an effective absorbing bandwidth of 4.8 GHz at a sample thickness of 2 mm was achieved. Such results demonstrate the validity of the co-doping strategy in designing microwave absorbers with high performance based on M-type ferrite.