By using one ultrathin NiO layer to replace the Pt capping layer in the Co/Pt multilayer with perpendicular anisotropy, we present direct evidence for the existence of antiferromagnetic interlayer coupling between the Co layers through the Pt layers thicker than 24 Å. The NiO capping layers play two key roles in the observation of antiferromagnetic interlayer coupling. One is the manipulation of the coercivity of the Co layer in contact with the NiO layer, the other is the enhancement of the electron reflectivities at the Co/Pt interfaces via the specular scattering effect at the Co-NiO interface. The thermal variation in the magnetization of the Co layer also plays an important role in the observed antiferromagnetic coupling due to its strong effect on the phase of electron reflectivity at the Co/Pt interfaces. The magnetization-dependent phase can lead to the ferromagnetic-antiferromagnetic transition of the interlayer coupling at high temperature. All these factors are combined together to realize the direct observation of antiferromagnetic interlayer coupling in the Co/Pt multilayer with perpendicular anisotropy.

In this work, we have demonstrated the existence of oscillatory antiferromagnetic interlayer coupling in the Co/ Pt multilayer with perpendicular anisotropy by using the sample configuration of ͓Pt͑6 Å͒ / Co͑4 Å͔͒ / Pt͑t Pt Å͒ / ͓Co͑4 Å͒ / Pt͑6 Å͒ / Co͑4 Å͔͒ / NiO͑20 Å͒. As a function of t Pt , there exists a transition of the interlayer coupling from ferromagnetic to antiferromagnetic. At t Pt Ͻ 25 Å, the interlayer coupling between Co layers is always ferromagnetic, while at t Pt Ͼ 25 Å, the antiferromagnetic interlayer coupling appears and its strength varies as a function of t Pt in such a way as to lend support to a theoretical model for a ͑111͒ Pt spacer.

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