  The problem of neutron scattering by the single magnetic atom is
theoretically considered in the second order perturbation theory. It is
demonstrated that elastic scattering of unpolarized neutron by magnetic atom is
skewed, i.e. contains the term with the symmetry of mixed product of the atom
magnetic moment and wave vectors of incident and scattered neutrons. The
problem of dynamical diffraction of unpolarized neutrons by the perfect
ferromagnetic crystal is investigated. The case is considered when the Bragg
condition is satisfied for two reciprocal lattice vectors. In this case neutron
skew scattering manifests itself as the dependence of the diffracted beam
intensity on the sign of the crystal magnetization. The calculations have been
done for the diffraction of unpolarized neutrons by Dy crystal. In case of the
diffraction by Dy the change of the intensity under the magnetization reversal
achieves 50%.
