STRUCTURE AND MAGNETIC-PROPERTIES OF MAGNESIUM FERRITE FINE POWDERS

Fine powders of magnesium ferrite, MgFe2O4, were produced through the sol-gel supercritical drying method, with two portions then being calc ined at 773 K and 1073 K. The powder structural and magnetic propertie s were determined from transmission electron microscope micrographs, x -ray diffraction, Mossbauer effect spectroscopy and magnetometry measu rements. The powder structure matched the MgFe2O4 spinel phase, with s mall amounts of alpha-Fe2O3 being observed in heated samples. As-produ ced powders were superparamagnetic at room temperature, with single ma gnetic domain particle behavior being observed at low temperatures, an d for the 1073 K heated sample. The particle size distribution for the as-produced powder was evaluated separately from the micrographs, by fitting the magnetization data to a weighted Langevin function and by fitting Mossbauer spectra taken at temperatures from 25 K to 298 K. Ve ry similar particle size distributions were found from all three metho ds. The average particle diameter was 11 nm for the as-produced powder , and increased for heated samples. The saturation magnetization and m agnetocrystalline anisotropy energy density values were both consisten t with bulk values, in contrast to the large differences between parti cle and bulk values described for other fine particle systems.