Polarized neutron reflectometry on lithographically patterned thin film structures

We report on the use of specular and off-specular polarized neutron reflectometry (PNR) for the study of magnetization reversal in patterned magnetic structures. We discuss the instrumental requirements and the measurement method and illustrate its potential by applying it to lithographically structured trilayer systems of the form (7.5 nm Au/20 nm Co/7.5 nm Au) prepared on oxidized Si wafers. In order to study the influence of the shape of the structures on the magnetic properties we prepared rectangular bars with a width of 1 μm and a length of 4 μm. The dots were arranged in a square lattice symmetry with a period of 10 μm. By using a two-dimensional position sensitive detector (PSD) we were able to record not only the specularly but also the off-specularly scattered intensity which has maxima at particular angles due to the in-plane periodicity of the discs. The second system that we studied is that of wires with a width of 2 μm and a period of 15 μm consisting of an exchange biased Co/CoO bilayer structure. By applying neutron spin analysis and monitoring the neutron reflectivity at a fixed angle of incidence as a function of an external magnetic field we were able to effectively study the magnetization reversal process in both systems.