Dipole-directed assembly of Fe3O4 nanoparticles into nanorings via oriented attachment

Abstract

We have developed a novel hydrothermal method to fabricate Fe₃O₄ ring-like nanostructures via oriented attachment of Fe₃O₄ nanoparticles through intermediate platelets with incorporation of inorganic salts. The obtained samples were characterized by X-ray diffraction (XRD) analysis, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selective-area electron diffraction (SAED), high-resolution TEM (HRTEM) and vibrating-sample magnetometer (VSM). A reasonable mechanism based on the self-assembly of magnetic Fe₃O₄ nanoparticles on graphene nanosheets using inorganic ions as crystal growth modifiers is proposed. The intrinsic dipole–dipole interactions between the individual magnetic Fe₃O₄ nanoparticles act as the driving force for nanoring formation. Saturation moment of the superparamagnetic Fe₃O₄ nanorings is much higher than that of the corresponding disassembled nanoparticles. The enhancement of saturation moment is due to the oriented ring-like assembly with synergistic magnetism. This study could provide an additional tool for fabricating other nanostructures via oriented attachment.