Field-dependent magnetic domain structure in antiferromagnetically coupled multilayers by polarized neutron scattering

We study the magnetic structure of antiferromagnetically (AF) coupled Co/Cu multilayers (MLs) with 10 or 40 bilayers under the influence of an external field by polarized neutron scattering in specular and off-specular geometry. We observe in the spin-flip channels off-specular intensities around the 1/2-order Bragg position. Based on simulations of the measured data within the distorted-wave Born approximation we find vertically correlated domains, and their domain size evolves for a sufficiently large number of bilayers along the ML stack. Small domains most likely at the top and large domains presumably at the bottom coexist within a single ML. The small domains gradually get aligned with the applied field direction around 0.5 kOe, whereas the bigger domains remain AF coupled up to 3.0 kOe, which is well above the apparent saturation field measured by conventional magnetometry methods. Moreover, we observe a double-peak structure at the 1/2-order position for the MLs with ten as well as 40 bilayers.