  In antiferromagnetic nanoparticles magnetization the linear component,
$\chi_{AF}$H superposed to the saturation one usually complicates the fit of
experimental data. We present a method based on scaling laws to determine the
variation of $\chi_{AF}$ with temperature and to find the temperature
dependence of the average magnetic moment $<\mu>$, without any assumption on
both the magnetization dependence on field or the moment distribution function,
whose relevance can also be estimated. We have applied this method to ferritin
and found that $<\mu>$ decreases with increasing temperature and that a
distribution function cannot be ignored. The fit with Langevin magnetization
law and lognormal moment distribution functions yielded parameters close to
those estimated with the scaling method. We also show that in general if the
distribution is ignored, and a single particle moment $\mu_p$ is used, $\mu_p$
presents an artificial systematic increase with temperature. This calls the
attention to the necessity of evaluating the effect of a size distribution
before concluding about the physical nature of the parameters variation.
