An increasing number of promising applications for future technology is arising from size constraints in nanoparticles (NPs) and from the chemical manipulation of their surfaces. In this work, we analyse the finite-size and surface effects on polyacrylic acid-coated Fe ₃ O ₄ NPs and oleic acid-coated γ -Fe ₂ O ₃ NPs by studying their magnetization curves at different temperatures. The measured thermal dependence of the saturation magnetization is no longer explained by the typical T ^3/2 Bloch law, yielding higher values than those expected for its exponent. When incorporated in polymeric matrixes to form magnetic transparent nanocomposites, the oleic acid-coated γ -Fe ₂ O ₃ NPs also deviate from Bloch’s law, but following the opposite trend observed in free coated NPs.

The elastic and optical properties of organically modified silicates prepared by ultrasonics aided polycondensation of tetraethoxysilane and polidimethylsiloxane are studied by means of high resolution Brillouin spectroscopy. Nuclear magnetic resonance data evidence the microseparation of the organic and inorganic phases for the systems with high content of polymer formation. The elastic and optical properties are clearly influenced by the change in microstructure. We propose a three component mechanical model that qualitatively explains the observed variation of the elastic constant $c_{11}$ versus molar fraction of dimethylsiloxane in these vitreous materials and develop a structural model that accounts for the observed dynamical behavior.