Microstructure of (Fe0.2Co0.8)(0.8)(Fe2.38Co0.62O4): A magnetic oxidation-resistant composite formed by coprecipitation

The metal-ferrite composite (Fe0.2Co0.8)(0.8)(Fe2.38Co0.62O4) has been studied by X-ray diffractometry measurements and high-resolution transmission electron microscopy. Spinel ferrite occurs in highly crystalline domains 100-150 nm in size, and the iron-cobalt alloy occurs in smaller and less-crystalline domains (10-20 nm). Both phases are heterogeneous in composition. The metal is embedded in the spinel phase, located near the edges, and overlaid by a poorly crystallized layer or misshapen regions containing small spinel crystals and amorphous phases. By annealing under vacuum up to 800 degrees C, the misshapen regions disappear and the size of the metallic regions increases. The concentration of iron in the metallic regions decreases and their structure changes to face-centered cubic, while the spinel becomes enriched in iron.