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 degrees C, and sintering temperature was fixed. While the M-phase (SrFe12O19) existed with hematite (Fe2O3) in the powder calcined at below 1220 degrees C, the pure M-phase was observed in the powder calcined at over 1240 degrees 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.