One-pot facile synthesis of cobalt oxide nanocubes and their magnetic properties

Co3O4 nanocubes with perfect shape were synthesized by a simple hydrothermal route in which Co3O4 was directly prepared in the one-pot process with aging temperature set at 160 °C without a subsequent calcination. In this study, as the whole process is sintering free, this can successfully avoid the agglomeration of nanoparticles and protect the integrity of perfect crystal form to the maximum extent. Cubic Co3O4 nanoparticles were characterized by field emission scanning electron microscopy, high-resolution transmission electron microscopy, and X-ray diffraction. Important factors influencing the nanoparticles’ formation were discussed, which include temperature, molar ratio of Co(Ac)2 to NaOH, reactant concentration, and the use of surfactant. Optical property was investigated by Raman spectroscopy and UV–Vis spectroscopy. Magnetic property measurement indicated that the sample exhibited a low Néel temperature (33 K) and bulk antiferromagnetic coupling due to geometric confinement of antiferromagnetic order within the nanoparticles. Below TN, the noteworthy exchange bias interaction between ferromagnetically coupled surface spins and underlying antiferromagnet-like coupled surface spins has also been observed.