Towards polarizing beam splitters for cold neutrons using   superparamagnetic diffraction gratings
  For holographic gratings recorded in superparamagnetic nanoparticle-polymer composites the diffraction efficiency should -- next to grating spacing, nanoparticle concentration and grating thickness -- depend on the strength of an external magnetic field and the incident neutron spin state. As a consequence, diffraction gratings should be tunable to act as mirrors for one spin state, while being essentially transparent for the other. Thus, polarizing beam splitters for cold neutrons become feasible. 
J. Klepp, I. Drevensek-Olenik, S. Gyergyek, C. Pruner, R. A. Rupp, M.   Fally
physics.ins-det