Nucleation and growth of magnetic nanoclusters on graphene moiré

Arrays of magnetic nanoclusters can have important technological implications, such as magnetic recording media for the new generation high-density data storage applications. In a search for an appropriate non-magnetic template for cluster arrays, van-der-Waals surfaces are a promising alternative to the reconstructed noble-metal surfaces. Recently, a new two-dimensional form of boronnitride was discovered [1]: highly regular structure of hexagonal boron nitride with a 3 nm periodicity and a 2 nm hole size can be formed by self-assembly on Rh(111). Graphene was also shown to form Moiré superstructures, with a periodicity of about 3 nm as a result of lattice mismatch, on Ir(111) [2] and Rh(111) [3] surfaces. This regular graphene nanostructure can serve as a template for the preparation of monodisperse nanocluster arrays [2], e.g., magnetic nanoclusters (NCs) [3]. On the other hand magnetic materials in contact with graphene are of interest for spintronic applications such as spin filter e.g. [4]. In this work, we use a graphene moiré grown on Rh(111) or Ir(111) as a template. Submonolayers of ferromagnetic metals including Ni, Fe and Co are deposited on the graphene moiré template at room temperature and at low temperature around 150 K and are investigated by scanning tunneling microscopy (STM) and by x-ray magnetic circular dichroism (XMCD). Additionally, we study the process of intercalation of ferromagnetic materials underneath the graphene layer.