Synthesis of hexagonal Co³⁺-substituted Sr-ferrites via ball-milling assisted ceramic process and their magnetic properties

M-type hexagonal SrCo_xFe_12−xO₁₉ (x = 0, 0.1, 0.2, and 0.3) have been synthesized by the ball-milling assisted ceramic process. The influence of Co substitutions on the crystalline structure, lattice strain, morphology, and magnetic behaviors has been investigated. The results show that a high-crystallized hexagonal SrCo_xFe_12−xO₁₉ is obtained when the precursor is calcined at 950 °C in air for 3 h. Lattice parameters and grain size of SrCo_xFe_12−xO₁₉ increase with the increase in substitution content (x). Hysteresis behavior varies with substitution content (x) and calcination temperature. M-type hexagonal SrCo_xFe_12−xO₁₉ (x = 0, 0.1, and 0.2), calcined at 950 °C, with uniaxial anisotropy exhibits a broad M–H loop and rectangular shape. At higher calcination temperature (1050 and 1200 °C) or substitution content (x) is equal to 0.3, the character of the hysteresis loop of SrCo_xFe_12−xO₁₉ changes from hard into semi-hard. The trend of specific saturation magnetization of SrCo_xFe_12−xO₁₉, calcined at 950 °C, increases with the decrease in lattice strains. SrFe₁₂O₁₉, calcined at 950 °C, has the highest specific saturation magnetization value (91.30 emu/g) and magnetic moment (17.36 µ _B). With the increase of calcination temperature, magnetic domain type of ferrites changes from a single magnetic domain to a multi-domain type.