Magnetic properties and microstructures of Fe/sub 3/O/sub 4/- gamma Fe/sub 2/O/sub 3/ intermediate state

Abstract

Magnetic properties and microstructures of Fe/sub 3/O/sub 4/- gamma Fe/sub 2/O/sub 3/ intermediary films were studied to clarify the origin of the coercivity increase which occurs in the oxidation process of Fe/sub 3/O/sub 4/ to gamma Fe/sub 2/O/sub 3/. Fe/sub 3/O/sub 4/ films were prepared on quartz substrates by electron beam evaporation and were gradually oxidized in air at 240 degrees C for 5 to 85 min. The maximum H/sub c/ of 1070 Oe was obtained at 50 min. The microstructure of the Fe/sub 3/O/sub 4/- gamma Fe/sub 2/O/sub 3/ intermediary films was directly investigated by high-resolution transmission electron microscopy (TEM). Specimens for the TEM observations were prepared by the 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 with the increase in H/sub c/ at the intermediate state.< >