Magnetic coupling in Fe/Nb multilayers: A neutron reflectivity study

Fe/Nb multilayers with different Nb layer thicknesses were investigated by neutron reflectometry. In accordance with previous work, we find that magnetic coupling of the Fe layers oscillates between ferro- and antiferromagnetic as a function of the Nb spacer layer thickness for $t_{\rm Nb} < 24~\rm\AA$. However, for larger Nb thicknesses only antiferromagnetic ordering, probably caused by dipolar coupling, is observed. Magnetic domains have lateral extensions of 0.7 to $\rm 10~\mu m$ as derived from off-specular reflectivity; the domain sizes oscillate correlated with the strength of the coupling