  The evolution of the magnetic moment in iron clusters containing 20 to 400
atoms is investigated using first-principles numerical calculations based on
density-functional theory and real-space pseudopotentials. Three families of
clusters are studied, characterized by the arrangement of atoms: icosahedral,
body-centered cubic centered on an atom site, and body-centered cubic centered
on the bridge between two neighboring atoms. We find an overall decrease of
magnetic moment as the clusters grow in size towards the bulk limit. Clusters
with faceted surfaces are predicted to have magnetic moment lower than other
clusters with similar size. As a result, the magnetic moment is observed to
decrease as function of size in a non-monotonic manner, which explains
measurements performed at low temperatures.
