Magnetic Iron Oxide/Mullite Nanocomposite Stable up to 1400°C

Magnetic nanocomposites consisting of spherical iron oxide particles of around 13 nm dispersed in a mullite matrix have been obtained by pyrolysis at 600°C of an aerosol generated from a solution of TEOS and iron and aluminum nitrate in methanol and a posterior heat treatment at 1200°–1400°C. Iron contents higher than the solubility limit of Fe in mullite (12 wt% Fe2O3) have been used to prepare the precursor samples. It should be emphasized that the new magnetic nanocomposite presents a saturation magnetization of 3.3 emu/g and a coercivity of 546 Oe at room temperature, and preserves its magnetic character up to 1400°C. This behavior reveals that mullite is an excellent matrix to keep the magnetic particles apart, avoiding sintering during the heat treatment and therefore making phase transformations difficult.