MAGNETIC-PROPERTIES AND MICROSTRUCTURES OF FE3O4-GAMMA-FE2O3 INTERMEDIATE STATE

Magnetic properties and microstructures of Fe3O4-γFe2O3 intermediary films were studied to clarify the origin of the coercivity increase which occurs in the oxidation process of Fe3O4-γFe2O3. Fe3O4 films were prepared on quartz substrates by electron beam evaporation and were gradually oxidized in air at 240°C for 5 to 85 min. The maximum IIc of 1070 Oe was obtained at 50 min. The microstructure of the Fe3O4-γFe2O3 intermediary films was directly investigated by high resolution transmission electron microscopy(TEM). Specimens for the TEM observations were prepared by ion thinning technique. The results indicate shrinkages in the films during the oxidation from 10 to 50 min. The results also show many dislocations, stacking faults and lattice defects, suggesting that the stresses in the films correlate to the increase in IIc at the intermediate state. © 1990 IEEE