Superparamagnetism in small Fe clusters on Cu(111)

Fe clusters of 105±2 atoms/cluster were mass selectively deposited onto Cu(111) at cryogenic temperatures. XMCD was used to measure temperature and direction dependent magnetization curves. The clusters are superparamagnetic at the lowest temperature measured (10 K). Their magnetization curves are consistent with magnetic moments of ≈2.5μ_B per atom which are thus enhanced over the bulk values. Within experimental accuracy, the clusters do not present magnetocrystalline anisotropy in the temperature range of 10 K to 60 K.