Interlayer exchange coupling in ordered Fe nanocluster arrays grown on Al2 O3 / Ni3Al(111)

We have combined magneto-optical Kerr effect, scanning tunneling microscopy, and x-ray magnetic circular dichroism to study the magnetic properties and the morphology of Fe nanoparticles grown on 2 ML thick Al2O3/Ni3Al(111)-(67×67)R12.2â with and without Pd seeding. The Ni3Al(111) substrate is ferromagnetic and shows two transition temperatures. The first, TC1=81±3 K, is attributed to a 20-30 nm thick slightly Ni enriched region; the second, TC2=240±12 K, is attributed to a much thinner and more strongly Ni enriched near interface region that contains Ni clusters embedded in the alloy matrix. The magnetic properties of the Fe cluster superlattice are strongly influenced by the superexchange coupling between Fe clusters and the underlying Ni clusters in that near interface region. Since the Ni clusters are at different distances from the oxide/metal interface, this coupling oscillates between ferro- and antiferromagnetic such that the overall magnetic moment is not increased by the Fe clusters. Pd seeding does not influence the magnetic properties of the system. The intrinsic Fe cluster properties, such as Curie temperature and easy magnetization axis, are accessed for T>TC2. We find out-of-plane easy magnetization axes and TC≠300 K for cluster sizes above 440 atoms.