  Nature creates electrons with two values of the spin projection quantum
number. In certain applications, it is important to filter electrons with one
spin projection from the rest. Such filtering is not trivial, since
spin-dependent interactions are often weak, and cannot lead to any substantial
effect. Here we propose an efficient spin filter based upon scattering from a
two-dimensional crystal, which is made of aligned point magnets. The
polarization of the outgoing electron flux is controlled by the crystal, and
reaches maximum at specific values of the parameters. In our scheme,
polarization increase is accompanied by higher reflectivity of the crystal.
High transmission is feasible in scattering from a quantum cavity made of two
crystals. Our findings can be used for studies of low-energy spin-dependent
scattering from two-dimensional ordered structures made of magnetic atoms or
aligned chiral molecules.
