The ferrosmectic phases are singular swollen lamellar phases whose peculiarity is to contain colloidal magnetic particles in their layers. A study of these newly invented systems by small angle neutron scattering is presented here. After a prior determination of the appropriate constant conditions performed on the bulk magnetic suspension, we analyse the smectic features of the phases when varying the swelling ratio and the particle concentration. One of their most striking trends is the evolution of the Bragg and small angle scatterings, which are very different from conventional lamellar phases. We conclude from these results that the usual Helfrich repulsion related to the membrane fluctuations might be modified here by another stabilizing effect due to the presence of the particles.