Relationship between nanoparticle growth and magnetic properties of magnetic nanocomposites

A description of the growth processes of maghemite (γ-Fe2O3) nanoparticles in a silica matrix (SiO2) synthesized under a classic sol–gel method is proposed in order to explain the observed magnetic behavior at different stages of the sample heat treatment. Analytical electron microscopy studies reveal the appearance of large iron oxide aggregates superimposed on a nanoparticle distribution. In addition to iron concentration, internal stresses generated inside the gel pore network contribute to nanoparticle aggregation and apparition of defects. Consequently, two mechanisms of attachment between particles may then come into stage depending on the silica network local arrangements: an imperfect oriented attachment and a non-oriented stress-assisted attachment.