  Magnetic small-angle neutron scattering (SANS) is ideally suited to provide
direct, reciprocal-space information of long-wavelength magnetic modulations,
such as helicoids, solitons, merons, or skyrmions. SANS of such structures in
thin films or micro-structured bulk materials is strongly limited by the tiny
scattering volume vis a vis the prohibitively large background scattering by
the substrate and support structures. Considering near-surface scattering
closely above the critical angle of reflection, where unwanted signal
contributions due to substrate or support structures becomes very small, we
establish equivalent scattering patterns of the helical, conical, skyrmion
lattice, and fluctuation-disordered phases in a polished bulk sample of MnSi
between conventional transmission and near-surface SANS geometries. This
motivates the prediction of a complete repository of scattering patterns
expected for thin films in the near-surface SANS geometry for each orientation
of the magnetic order with respect to the scattering plane.
