Presently two different approximations exist in order to explain the assymmetrically broadened lineshapes observed in ultrafine iron oxides and iron oxy-hydroxides. One, due to Mørup et al. /1/ uses a simple pre-relaxation model for the total sublattice spin of the particle, together with a particle size distribution. By adjusting suitable distribution parameters and the anisotropy constant, indeed a reasonable representation of the experimental results can be obtained. The second approach, as we proposed in previous papers /2, 3/ considers the observed reduced magnetic fields mainly to be due to the surface cations being gradually decoupled from the interior of the particle. Unfortunately neither a detailed shape of this field reduction near the surface can as yet been given, nor a clear description of the changes of the Mössbauer fraction f near the surface. However here too a field function can be proposed and suitable parameters be adjusted to match the experimental results ; these parameters are the maximum inside field Hoi, a Gaussian dispersion σs of the surface field, a small dispersion σB on the interior field due to residual effects of particle size (which in this model is a second order effect), and the fraction p of surface cations relative to the total number of cations.