Magnetic properties of M-type strontium ferrites with different heat treatment conditions

The effects of heat treatment conditions on the magnetic properties and microstructure of M-type strontium ferrite according to calcination temperature were analyzed. Strontium ferrite Sr0.06Ca0.52La0.52Fe11.68Co0.22O19 magnetic powder was prepared by a standard ceramic process. During experiments, the calcination temperature was varied from 1180 to 1260 °C, and sintering temperature was fixed. While the M-phase (SrFe12O19) existed with hematite (Fe2O3) in the powder calcined at below 1220 °C, the pure M-phase was observed in the powder calcined at over 1240 °C. With an increase in the calcination temperature, the magnetization of the calcined powder increases, meanwhile, the coercivity decreases. The magnetization is improved by decreasing the lattice constant c and activating the Fe3+–O–Fe3+ superexchange interaction, and the coercivity decreases by the large particle sizes due to the grain growth.