Magnetic coupling across the antiferromagnetic–antiferromagnetic interface

We investigate the magnetic coupling across the antiferromagnetic–antiferromagnetic (AFM–AFM) interface for the prototypical CoO-NiO bilayer system where the bulk Néel temperature (T_N) of NiO is higher than that of CoO. Using the temperature-dependent exchange-scattered electron intensities from the surface AFM lattice, the surface T_N of CoO was estimated as a function of the CoO/NiO film thicknesses. Our results show that the surface T_N of CoO layers is enhanced significantly from its bulk T_N value and approaching the T_N of the NiO layers, as the thickness of the CoO layers is reduced to the monolayer limit. Thus, thinner CoO layers are found to have higher T_N than thicker layers on NiO, contrasting with the expected finite-size behavior. In addition to the short-range magnetic exchange coupling at the CoO-NiO interface, we observe the existence of a longer-range magnetic coupling across the interface, mediated by the magnetic correlations. Thus, the magnetic proximity effect is attributed to a combination of a short-range and a weaker long-range magnetic coupling, explaining the long AFM order propagation length in AFM–AFM superlattices and bilayers. Further, our results indicate a new approach to tune the AFM Néel temperature by varying the individual layer thickness of the bilayer system through the magnetic proximity effect. (paper)