Morpho-Structural and Magnetic Properties of CoFe₂O₄/SiO₂ Nanocomposites: The Effect of the Molecular Coating

The use of magnetic nanoarchitecture in several applications is often limited by the lack of noninteracting particles, due to the frequent presence of clusters and aggregates of particles. Here, we report an investigation of the interparticle interactions by changing the molecular coating on ∼5 nm CoFe2O4 nanoparticles embedded in a silica structure. The magnetic investigation at a low temperature allows revealing the key role of organic ligands in tuning the morpho-structural properties of hybrid materials. Cobalt ferrite-coated nanoparticles were prepared by the polyol method using triethylene glycol as a co-reagent (CFOT) and by the exchange ligand process using dihydroxyhydrocinnamic acid (CFOH). Then, magnetic mesoporous silica nanocomposites have been prepared starting from CFOT (CFOTS) and CFOH (CFOHS). For the CFOTS sample, the interparticle distance did not change after coating, whereas the CFOHS sample showed an increase in the interparticle distance by 23%. This value has been obtained by investigating interparticle interactions by remanence techniques, which represent a good approach to determine the approximated values of interparticle distances in complex systems. The measurements showed that the silica coating produces a reduction of 47% in the dipolar interaction strength for the CFOHS sample, whereas no significant change was observed for the CFOTS sample. The differences in magnetic response upon varying the molecular coating of nanoparticles are due to the different interactions of the molecular ligands with silica, resulting in a change of interparticle distances and then magnetic interactions