Spherical Nanoporous Assemblies of Iso-Oriented Cobalt Ferrite Nanoparticles: Synthesis, Microstructure, and Magnetic Properties

Nanoporous spherical assemblies of iso-oriented cobalt ferrite nanoparticles with a high surface area were prepared via a normal micelles process. The spherical magnetic assemblies were coated with a silica layer through an inverse micelles route. The microstructure and morphology were studied by X-ray diffraction, transmission electron microscopy and N 2 -physisorption techniques. The primary CoFe 2 O 4 nanocrystalline particles (∼7 nm) assemble into spherical nanoporous aggregates with an average size of about 50−60 nm and the coating process leads to core−shell nanostructures with an amorphous 7−8 nm thick silica shell that covers the spherical assemblies homogeneously. The magnetic properties of both uncoated and silica-coated nanostructures were also investigated.