The impact of Co/La ratios on microstructure and magnetic properties of the Sr0.75−xCa0.25LaxFe12−yCoyO19 hexaferrites

• Sr0.75−xCa0.25LaxFe12−yCoyO19 hexagonal ferrites were synthesized according to a ceramic process.
• There is a single magnetoplumbite phase in the samples with y/x from 0.3 to 0.6, and when y/x is above 0.7, the CoFe2O4 phase is observed.
• Br, Hcb and (BH)max of the magnets first increase with y/x from 0.3 to 0.6, and then, decrease when y/x continues to increase.
• Hcj of the magnets first increases with y/x from 0.3 to 0.9, and then, decreases when y/x is above 0.9.
• The rectangularity of the demagnetizing curves for the magnets decreases with the increase of y/x.

Hexagonal ferrite Sr0.75−xCa0.25LaxFe12−yCoyO19 magnetic powder and magnets were synthesized according to a ceramic process. The phase compositions of the magnetic powder samples were determined by X-ray diffraction. There is a single magnetoplumbite phase in the samples with y/x from 0.3 to 0.6, and when y/x>0.6, the CoFe2O4 phase is observed. The micrographs of the sintered magnets were observed by a field emission scanning electron microscopy. The magnets have formed the hexagonal structures and the particles are distributed inhomogeneously. The impact of Co/La ratios on magnetic properties of the magnets was studied systematically. The remanence, magnetic induction coercivity and maximum energy product of the magnets first increase with y/x from 0.3 to 0.6, and then decrease when y/x>0.6. However, the intrinsic coercivity of the magnets first increases with y/x from 0.3 to 0.9, and decreases when y/x>0.9. The rectangularity of the demagnetizing curves for the magnets decreases with increasing y/x.