Experimental evidence of dipolar interaction in bilayer nanocomposite magnets

We use magnetic thin film hard/non/soft-magnetic trilayer systems to probe the nature of the hard-soft phase interaction and the role played by dipolar fields in one-dimensional (d) magnetic systems. We have systematically investigated six wedge samples where the thickness of a Cu spacer layer (t _Cu) was gradually changed to create a varying interfacial effect on the interaction between a CoPt hard layer and a Fe soft layer. Magneto-optical Kerr effect was used to obtain the magnetization loops at 28 points on each sample, and the nucleation field (H _N ) as a function of t _Cu was employed to characterize the layer interaction as a function of t _Cu. H _N (t _Cu) show a RKKY oscillatory behavior in addition to a non-negligible dipolar contribution, which had an exponential dependence. The dipolar term, which cannot be always neglected, is affected by the interface roughness and also by the CoPt crystallinity. Therefore, we cannot always consider exchange coupling to be the dominant interaction in one-d hard-soft magnetic bilayer systems, particularly, during magnetic reversal.