The dynamical properties of $\gamma$-${\mathrm{Fe}}_2$ ${\mathrm{O}}_3$ particles, dispersed in a polymer, were investigated by ac susceptibility ($2\times {10}^{-2\mathrm{}} \mathrm{Hz}<~\nu <~{10}^4\mathrm{Hz}$) and Mössbauer spectroscopy measurements. The variation of the average blocking temperature as a function of the measuring time is satisfactorily described by a model which accounts for interparticle interactions by a statistical calculation of the dipolar energy for a disordered assembly of particles with a volume distribution and easy axes in random position.

Measurements have been performed of the nuclear-magnetic-resonance longitudinal and transverse relaxation and the self-diffusion coefficient of deionized water confined in the porous space of a silica glass. The average pore diameter of the glass is 3.5 nm, and the experiments were conducted with different degrees of fluid filling. All three physical quantities were found to be linearly dependent on filling provided this was in excess of the amount of water corresponding to one monolayer, in agreement with theoretical predictions based on geometrical considerations. However, a deviation is observed below one monolayer, which is interpreted as a modification of the liquid-solid interface interaction, which causes the water molecules to become less mobile.