The effect of pinned uncompensated moments on the exchange bias in Ni81Fe19/Ni50Mn50/Ni81Fe19 trilayers

In this work, we prepared Ni81Fe19/Ni50Mn50 bilayers and Ni81Fe19/Ni50Mn50/Ni81Fe19 trilayers by magnetron sputtering. In order to determine whether the main contribution to the exchange bias is the ferromagnetic (FM)/ antiferromagnetic (AFM) interface effect or the AFM bulk effect, the relationships between the exchange bias field and the top layer thickness, AFM layer and bottom layer were studied. The measured data show that the values of the exchange bias field were much smaller for trilayers than bilayers. This reduction is mainly caused by the thickness of the top Ni81Fe19 layer; the value of the exchange bias field becomes small when the thickness of the top layer is large. It was also observed that the exchange bias field decreases with the thickness of the bottom Ni81Fe19 layer, which is consistent with the top layer thickness dependence. Such a behavior can be explained by the pinned uncompensated moments inside the bulk of the AFM layer. The results indicate that the Ni50Mn50 layer contains a lower amount of pinned uncompensated moments in the Ni81Fe19/Ni50Mn50/Ni81Fe19 trilayer than in the bilayer films, which leads to a reduction in the exchange bias field.