Polarized neutron reflection as a probe of magnetic films and multilayers

The application of polarized neutron reflection (PNR) to the study of the magnetic properties of thin films and multilayers is described. It is demonstrated that PNR provides a means of directly determining the magnetization-vector profile in multilayers of known layer thickness and layer density. Thus, the magnetization reversal process in these systems can be directly studied. A matrix method is presented which can be used to calculate the spin-dependent reflectivity from a multilayer with general in-plane orientation of the magnetic moment in each layer. In addition, we show that behavior of the spin asymmetry is dominated by multiple reflections and refraction just above the critical wave vector, but with increasing wave vector, such processes become progressively less important, and the response moves towards a ``diffraction limit'' in which a Fourier-transform approximation to the exact result can be used. The ideas in this paper are illustrated by a number of examples, including the exchange-biased structure Ag/Fe-Ni/Cu/Fe-Ni/Fe-Mn/Si.