Samples containing Fe nanoparticles dispersed in SiO2 were prepared by high energy ball milling. We have studied the variation with the milling time of both the saturation magnetization and the coercive force of these samples. The rapid increase of coercivity with the decrease of temperature observed in the low temperature range suggested the presence of superparamagnetic particles in the samples. Nevertheless, our experimental data were in poor agreement with the well‐known T1/2 law describing the coercive force of superparamagnetic particles. Coercivities as high as 540 and 850 Oe were obtained for samples with x=0.3 at room temperature and at 1.7 K, respectively. From the analysis of the temperature dependence of the saturation magnetization the spin wave stiffness constant was obtained. This quantity evidenced the enhancement of the thermal demagnetization associated with the reduction in size.