Fe/Fe-oxide core-shell systems obtained by inert-gas condensation and Au80Fe20 nanostructured alloys prepared by fast-quenching techniques followed by thermal treatment have been studied by polarised small-angle neutron scattering (SANS). The particle-size distribution was derived from the fit of the scattering curves. In the core-shell samples, the results support the model of a magnetic iron core surrounded by a surface layer (oxide shell) with a reduced magnetisation. The SANS measurements on the Au80Fe20 alloys do not show any appreciable magnetic signal, indicating that the iron precipitates have a superparamagnetic behaviour. Thermal treatment induces the formation of small precipitates of atomic size.