Exchange-bias-like coupling in a ferrimagnetic Fe/Tb multilayer

Field cooling of a transition metal-rare earth (TM-RE) Fe/Tb-multilayer system is shown to form a double hysteresis loop with exchange-bias-like shifts along and opposite to the field cooling axis below the ordering temperature of the RE. The measurement of the polarized neutron reflectivity at various applied fields confirms an antiferromagnetic alignment between the individual layers of Fe and Tb associated with a significant value of the magnetic moment for the Tb layers, even at room temperature. We attribute the shifts of the hysteresis loops to the formation of 2π-domain walls by the interface moments that are pinned by the magnetically hard Tb layers forming bidomainlike states in this layered artificial ferrimagnetic system. We conclude that the exchange bias in Fe/Tb-multilayers, the RE layers being on either sides of the TM layers, is caused by the formation of 2π-domain walls in the Fe layers thus excluding an explanation in terms of π-domain walls, which are believed to be responsible for the exchange bias in other RE-TM bilayer systems.