The behavior of a neutron polarization vector for neutrons passing through magnetic media characterized by a magnetic fluctuation tensor is described by Bloch-type equation. Coherent and incoherent spin flow motions on the surface of an unit three-dimension sphere are reflected by the equation. The applicability of the equation is based on two factors: (a) the SU(2) group analysis of the neutron spin behaviour in a magnetic field; and (b) consecutive averaging of spin trajectories in the SU(2) group manifold over all neutrons passing through a thin sample layer. Halpern-Holstein's and Maleyev-Ruban's depolarizations are discussed.