Magnetism of small Fe clusters on Au(111) studied by x-ray magnetic circular dichroism

Epitaxial growth of Fe on a reconstructed Au(111) surface leads to the formation of self-organized fcc Fe dots and stripes with increasing coverage. Using the sensitivity of x-ray magnetic circular dichroism (XMCD) and sum rule analysis, the changes in the magnetic properties in the low thickness range from ~0.1% of a monolayer (ML) to 4 ML, covering the unidimensional (1D) coalescence around ~0.3 ML and the two-dimensional percolation limit around ~1 ML have been determined. The evolution of the spin moment (mₛₚᵢₙ) as a function of the thickness is correlated to the morphological transition. In particular, mₛₚᵢₙ increases sharply at the 1D coalescence, what is attributed to a transition from a low-spin to a high-spin magnetic phase. We also observe a flipping of the easy axis of magnetization at the 1D coalescence from in-plane to out-of-plane. This unusual behavior is ascribed to the strong in-plane relaxation of the Fe films due to the particular pseudomorphic growth of Fe on the reconstructed Au(111) surface.