A modified model for superparamagnetic relaxation is presented. This model combines the conventional superparamagnetism with the recently described effect of collective excitations of the magnetization around an easy direction. The marked effects of particle size are also discussed. The model explains the reduced value of the observed hyperfine fields and the asymmetric line shapes of Mössbauer spectra of small particles of magnetically ordered compounds. Chemisorption of different molecules on Fe3O4 particles shows that the anisotropy energy is sensitive to surface effects