Magnetic profiles and coupling in Fe/Cr(110) superlattices

In epitaxial Fe/Cr superlattices the coupling between the Fe layers oscillates between antiferromagnetic (AFM) and ferromagnetic as a function of the Cr layer thickness tCr. The period of the oscillation is the same for superlattices grown with (211) and (100) orientations. We measured the coupling of Fe/Cr(110) superlattices consisting of three identical Fe layers. The magnetization curves were characterized by two to four levels, M/Ms=±1 or ± $\frac\Box1\Box\Box3\Box$ . Polarized neutron reflectometry identified the direction of the magnetization of each Fe layer and showed that the levels M/Ms=± $\frac\Box1\Box\Box3\Box$ were not always due to AFM alignment of the central layer, but rather it was found that, in spite of the structural similarity, the bottom Fe layer had a different coupling strength from the top Fe layer. The magnetic coupling must be sensitive to small structural differences at the interface. Furthermore, the measurements indicate an unexpected periodicity for Fe/Cr(110) superlattices.