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 tran smission electron microscopy. Spinel ferrite occurs in highly crystall ine domains 100-150 nm in size, and the iron-cobalt alloy occurs in sm aller and less-crystalline domains (10-20 nm). Both phases are heterog eneous in composition. The metal is embedded in the spinel phase, loca ted near the edges, and overlaid by a poorly crystallized layer or mis shapen regions containing small spinel crystals and amorphous phases. By annealing under vacuum up to 800 degrees C, the misshapen regions d isappear and the size of the metallic regions increases. The concentra tion of iron in the metallic regions decreases and their structure cha nges to face-centered cubic, while the spinel becomes enriched in iron .