Mullite based iron magnetic nanocomposite powders were synthesized by reduction of sol-gel prepared mullite-iron oxide solid solution in hydrogen flow. Structural characterization studied by TEM revealed that two types of α-iron nanoparticles existed in mullite matrix. The α-iron nanoparticles with the size around hundreds of nanometers appeared as inter-type grains, while those around 10 nm were embedded in the grains of mullite. The magnetic properties of nanocomposites suggest that the intergranular and intragranular α-iron nanoparticles had the ferromagnetic and superparamagnetic behavior at room temperature, respectively. The oxidation behavior of nanocomposite powders showed that there existed two different oxidation stages of α-Fe nanoparticles.
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