Impacts of heat treatment on the microstructure and magnetic properties of LaPr-Co substituted M-type CaSr hexaferrite

The M-type hexaferrite Ca0.4Sr0.3(La0.8Pr0.2)0.3Fe11.76Co0.24O19 was synthesized by the solid-state reaction method. The effects ofcalcination temperature and sintering temperature on the microstructural and magnetic properties have been carefullyinvestigated. The X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and a permanent magneticmeasuring system were used to investigate the microstructure and magnetic properties of the samples. Single-phase hexaferritepatterns are observed for the hexaferrite magnetic powders at different temperatures from 1210 to 1270 oC for 2 hrs. The FESEMimages of the magnets show that the hexagonal structures have been formed in the magnets, and the grains in themagnets are distributed evenly. With the increase of calcination temperature, the remanence (Br) and maximum energyproduct [(BH)max] increase from 1210 oC to 1270 oC, while the magnetic induction coercivity (Hcb) and intrinsic coercivity (Hcj)increase from 1210 oC to 1250 oC, and then decrease when the calcination temperature ≥ 1250 oC. With the increase ofsintering temperature, the remanence (Br) and maximum energy product [(BH)max] increase from 1180 to 1200 oC, while themagnetic induction coercivity (Hcb) and intrinsic coercivity (Hcj) increase from 1180 to 1195 oC, and then decrease when thecalcination temperature ≥ 1195 oC.