Fe3O4 nanoparticles and nanocomposites for applications in biomedicine and the ICTs: Nanoparticle aggregation, interaction and effective magnetic anisotropy

Magnetite nanocomposites containing Fe₃O₄ nanoparticles (NPs) retain high interest and long-lasting appeal as multifunctional materials for sensors and actuators with applications to biomedicine as well as to the area of Information and Communication Technologies (ICTs). Most of the current chemical routes to synthesize ferrimagnetic Fe-oxide NPs provide a quite reproducible output and a well-defined chemical composition and structure. The relatively easy synthesis procedure explains the widespread use of both bare and suitably coated Fe₃O₄ NPs for a variety of applications, especially in the biomedical field. In this work, magnetite nanoparticles with a size of 5-6 nm were synthesized by thermal decomposition of Fe(acac)₃ and subsequently coated with a silica shell exploiting a water-in-oil synthetic procedure. The average radius and size distribution function of as-produced powders, comprised of either bare (Fe₃O₄) or silica-coated (Fe₃O₄@silica) nanoparticles, have been obtained by TEM image analysis. The Fe₃O₄ nanoparticles have a spheroidal shape characterized by a narrow Gaussian bell distribution centered at 5.65 nm ± 0.13 nm; the Fe₃O₄@silica nanoparticles evidenced a log-normal particle size distribution with a mean diameter of 25.61 nm ±8.43 nm, each silica particle typically enclosing more than one magnetic nanoparticle.