Controlled synthesis of Co3O4 nanocubes under external magnetic fields and their magnetic properties

Abstract

Regular tricobalt tetraoxide (Co₃O₄) nanocubes with tunable sizes have been synthesized by a simple magnetic field assisted hydrothermal reaction. In contrast to other traditional methods, no surfactant is added to the reaction system, the morphology of the product is controlled by the application of an external magnetic field and the size distribution of the product is tuned by simply modifying the ratio of distilled water to ethanol in the solvent. The growth process of Co₃O₄ nanocubes is investigated and discussed in detail. It is found that the differences in polarity and dielectric constant between distilled water and ethanol and thus the difference of cobalt coordination ions concentration in the different solvents are the major factors that determine the final size distribution of Co₃O₄ nanocubes. Magnetic properties of Co₃O₄ nanocubes synthesized under (MF) and not under (ZF) an external magnetic field are then investigated. It is believed that during their growth, the alignment of spins in the Co₃O₄ particles and thus the magnetic and crystal lattices of Co₃O₄ are influenced by the external magnetic field. Spins in MF arrange in a less-ordered manner and cannot be totally compensated by each other, therefore makes them have a stronger tendency to align into an ordered figuration, which leads to a relatively larger magnetization and higher Néel temperature (T_N) of MF comparing to sample ZF.