Fe/Cr multilayers: Effect of annealing on the spin structure and magnetoresistance

The spin structure of antiferromagnetic Fe/Cr multilayers has been investigated by polarized neutron reflectivity. Measurements were taken on freshly sputtered films as well as films annealed at different temperatures. For annealing temperatures up to 350°C adjacent Fe layers were found to remain antiferromagnetic, but the coupling strength gradually decreases. In multilayers annealed at higher temperature both antiferro- and ferromagnetic phases are present. In all cases the magnetoresistance is proportional to the amount of antiferromagnetism. The presence of off-specular, diffuse scattering around the antiferromagnetic Bragg peak indicates that the magnetic domains are laterally limited; however, their size is not correlated directly to the magnetoresistance.