  The magnetic ground state of antiferromagnetically coupled Gd/Fe multilayers
and the evolution of in-plane domain walls is modelled with micromagnetics. The
twisted state is characterised by a rapid decrease of the interface angle with
increasing magnetic field. We found that for certain ratios M(Fe):M(Gd), the
twisted state is already present at low fields. However, the magnetic ground
state is not only determined by the ratio M(Fe):M(Gd) but also by the
thicknesses of the layers, that is the total moments of the layer. The
dependence of the magnetic ground state is explained by the amount of overlap
of the domain walls at the interface. Thicker layers suppress the Fe aligned
and the Gd aligned state in favour of the twisted state. Whereas ultrathin
layers exclude the twisted state, since wider domain walls can not form in
these ultrathin layers.
