  We investigate the interlayer exchange coupling in Fe/MgO/Fe and Fe/MgO/Co
systems with magnetic Fe nanoclusters embedded in the MgO spacer. Samples are
grown by molecular beam epitaxy (MBE) and utilize wedged MgO films to
independently vary the film thickness and the position of the Fe nanoclusters.
Depending on the position of the Fe nanoclusters, the bilinear coupling (J1)
exhibits strong variations in magnitude and can even switch between
antiferromagnetic and ferromagnetic. This effect is explained by the magnetic
coupling between the ferromagnetic films and the magnetic nanoclusters.
Interestingly, the coupling of Fe nanoclusters to a Co film is 160% stronger
than their coupling to a Fe film (at MgO spacing of 0.56 nm). This is much
greater than the coupling difference of 20% observed in the analogous thin film
systems (i.e. Fe/MgO/Co vs. Fe/MgO/Fe), identifying an interesting nano-scaling
effect related to the coupling between films and nanoclusters.
