Magnetic off-specular neutron scattering from Fe/Cr multilayers

The magnetic structure of a [Cr(9 angstroms)/⁵⁷Fe (68 angstroms)]×12 multilayer on sapphire substrate has been studied with polarized neutron reflectometry. The intensity distribution was measured over a broad range of incident and outgoing angles with spin analysis. The specular and off-specular intensities of the first and second-order Bragg-peaks (determined by the bi-layer thickness) and those at the half-order positions (due to an antiferromagnetic coupling) were measured. Off-specular scattering arranged into sheets running across the antiferromagnetic half-order positions is spread over an appreciable range perpendicular to the specular line. It consists of almost totally spin-flip scattering. Nearly no experimental evidence of the peak at the position of antiferromagnetic superstructure is found in the spin-flip specular channel. The intensity of the diffuse scattering scales with the intensity of the Bragg peaks, which is a function of the external magnetic field. These findings result in a picture of antiferromagnetic domains, rather than in the model of homogeneous magnetized neighbouring layers with a magnetization coupling angle.