Microstructure and magnetic characterization of the Sm-CoMn co-substituted SrCaM hexagonal ferrites

A series of Sm-CoMn substituted hexagonal ferrites with chemical composition of Sr0.85-xCa0.15SmxFe12-y(Co0.5Mn0.5)yO19 (0.00 ≤ x ≤ 0.60, (0.00 ≤ y ≤ 0.50) were synthesized by the solid-state reaction method. Microstructure and magnetic properties of the hexaferrites have been investigated by the X-ray diffraction, field emission scanning electron microscopy and a permanent magnetic measuring system. A single magnetoplumbite phase is exhibited in the hexaferrites with the substitutiom of Sm (0.00 ≤ x ≤ 0.12) and CoMn (0.00 ≤ y ≤ 0.10) contents. For the hexaferrites containing Sm (x ≥ 0.24) and CoMn (y ≥ 0.20), impurity phases are observed in the structure. The FESEM micrographs exhibit that the hexaferrites with different Sm-CoMn contents have formed hexagonal structures and the grain size of the hexaferrites remains unchanged with increasing Sm-CoMn content. The remanence (Br), Hk/Hcj ratios, and maximum energy product [(BH)max] decrease with increasing Sm-CoMn content (0.00 ≤ x ≤ 0.60, (0.00 ≤ y ≤ 0.50). Instrinsic coercivity (Hcj) and magnetic induction coercivity (Hcb) increase with increasing Sm-CoMn content (0.00 ≤ x ≤ 0.12, 0.00 ≤ y ≤ 0.10), and then decrease with increasing Sm-CoMn content (0.12 ≤ x ≤ 0.36, 0.10 ≤ y ≤ 0.30), while for the hexaferrites with Sm (x ≥ 0.36) and CoMn (y ≥ 0.30), with increasing Sm-CoMn content, Hcj increases and Hcb decreases.