Facile sonochemical synthesis of high-moment magnetite (Fe ₃O₄) nanocube

Monodisperse magnetite nanocubes with uniform particle size of about 80 nm have been synthesized in aqueous medium by single reaction sonochemical method using inexpensive and non-toxic metal salt (FeSO₄·7H ₂O) as reactant. The crystallinity of the magnetite nanocube is enhanced by annealing treatment up to 600 C with uniform shape and size distribution, after that a distortion in shape and a broad size distribution are obtained at 700 C annealing temperature. The magnetic characterization of the nanoparticles reveals saturation magnetization of 91 emu/g at 5 K for as-synthesized sample and 94.8 emu/g for the sample which annealed at the temperature of 600 C in a vacuum chamber. However, the saturation magnetization has been observed to decrease with further increase in annealing temperature and this has been attributed to the presence of a thin magnetic dead layer at the surface caused by shape anisotropy distortion and broken exchange bonds, and spin canting on the surface of the particles in addition to the formation of a small amount of maghemite phase.