Magnetism in Fe nanoclusters - from isolated particles to nanostructured materials

We have studied the evolution of the magnetic behaviour of Fe nanoclusters from isolated particles adsorbed on a surface and exposed in UHV to dense interacting assemblies. The clusters were produced by a UHV-compatible gas aggregation source and were studied in situ by synchrotron radiation techniques based on dichroism and ex situ after transfer into a UHV-capable vibrating sample magnetometer. Isolated and exposed 250-atom Fe clusters deposited on HOPG substrates exhibit enhanced orbital and spin magnetic moments that decay towards the bulk value with increasing size or with increasing particle density on the surface. The individual particles appear to be magnetically isotropic but a strong in-plane anisotropy develops as the coverage is increased to a complete cluster monolayer. At low temperature, thick cluster films have an asperomagnetic configuration that develops into a two-dimensional correlated super spin glass with increasing temperature.