Experimental determination of the magnetic phase diagram of Gd/Fe multilayers

By combining magnetization, Kerr effect measurements, and polarized neutron reflectometry we have determined the magnetic state of [Fe 35 Å/Gd 50 Å]×15 multilayers at different points of the $H-T$ phase diagram. We confirm the predictions of Camley and co-workers for an idealized magnetic superlattice with antiferromagnetic interfacial coupling. The magnetic moments of the Fe and Gd layers are opposite with those of Gd becoming larger below a compensating temperature. The magnetic moments are aligned parallel to the applied magnetic field below a certain value, and then they take a twisted arrangement as the field is increased. The transition may start from the surface or the interior, depending on whether the magnetization of the surface layer is oriented in or opposite to the field direction.