Antiferromagnetic order in a Dy/Er superlattice.

We present results on magnetic ordering in a Dy(60 \AA{})/Er(60 \AA{}) superlattice made up of two magnetic rare earths exhibiting in-plane and perpendicular anisotropies. Neutron diffraction reveals that the helical magnetic coherence of dysprosium propagates through paramagnetic erbium layers, without inducing spin ordering in erbium. Below the ordering temperature of dysprosium individual ferromagnetic dysprosium layers show antiparallel stacking through magnetic erbium. This antiferromagnetic phase of dysprosium is irreversibly destroyed by a 5.5-kOe external magnetic field and replaced by a ferromagnetic order between dysprosium layers. Magnetization measurements indicate that this irreversibility could arise from an energy barrier between parallel and antiparallel stacking of ferromagnetic dysprosium layers.