Polarized-neutron reflectometry

Abstract

Polarized-neutron specular reflectometry (PNR) was developed in the 1980s as a means of measuring depth-resolved magnetization in flat films with characteristic thicknesses from 2 to 5000 Å. PNR has been widely used to study homogeneous and heterogeneous magnetic films, as well as superconductors. Starting from simple profiles, and gradually solving structures of greater complexity, PNR has been used to observe or clarify phenomena as diverse as the magnetism of very thin films, the penetration of fluxoids in superconductors, and the magnetic coupling across non-magnetic spacers. Although PNR is considered to be a probe of depth-dependent magnetic structure, laterally averaged in the plane of the film, the development of new scattering techniques promises to enable the characterization of lateral magnetic structures. Retaining the depth-sensitivity of specular reflectivity, off-specular reflectivity can resolve in-plane structures over nanometer to micron length scales. Presently limited by the neutron fluxes available, neutron reflectivity is expected to blossom in the next century, thanks to the increased brightness of the neutron beams, due not only to continuing improvements in neutron optics, but especially to the advent of second-generation spallation neutron sources.