EFFECTS OF ADDITIVES ON MAGNETIC-PROPERTIES OF SHEET SR-BA FERRITE MAGNETS

Sr0.75Ba0.25Fe12O19 hexagonal ferrite has attracted much attention due to its large (BH)(MAX) values and workability. We have prepared sheet magnets by the Dr. Blade method. To examine the effects of additives, such as SiO2, TiO2, Al2O3, and Cr2O3, on magnetic properties of sheet magnets, we used VSM magnetometer, x-ray diffraction, and Mossbauer s pectrometer. The crystal structure is found to be a magnetoplumbite of typical M-type hexagonal ferrite, but the alpha-Fe2O3 phase develops with increasing additives concentration. Using our refined computer pr ogram, we have analyzed the Mossbauer spectra in the temperature range from 13 to 800 K. The Mossbauer spectra indicate that the line intens ity for the 12k site is reduced with increasing SiO2 concentration, wh ich is different from the reports of Fe-substituted Ba ferrite. This s uggests that the developing alpha-Fe2O3 phase is related to 12k sites. The isomer shifts show the charge states of Fe ions is ferric. When t he additives concentrations increase, the Curie temperatures, T-c go d own. One sextet for alpha-Fe2O3 phase still persists above T-c, so it suggests that the high-T-c values do not result from alpha-Fe2O3. Whil e Al2O3 and Cr2O3 additives increase coercive force H-c, the other add itives reduce it.