Neutron diffraction from magnetic spiral structures is governed by strong s
election rules for the polarization of the outgoing beam. When the sample i
s entirely of one chirality - for instance a right-handed spiral - the neut
rons diffracted by some Bragg reflections are fully polarized. While the sc
attering theory has been formulated long ago, attempts to controllably modi
fy the population of left-handed and right-handed spiral domains in natural
magnetic structures (which for instance occur in some rare-earth metals) h
ave been largely unsuccessful. In contrast, we have been able to imprint he
lical magnetic structures in La/Fe multilayers (each layer approximately 30
Angstrom thick) simply by rotating the growing sample in a weak external h
eld (3 Oe). A first estimate is given of the efficiency of these multilayer
s as polarizers of neutron beams. (C) 1999 Elsevier Science B.V. All rights
reserved.