Static and dynamic magnetic behaviour of iron nanoclusters on magneticsubstrates

Abstract

The static and dynamic magnetic behaviour of Fe nanoclusters with controlledsizes in the range 140–270 atoms (1.5–1.8 nm) deposited in situ froma gas aggregation source on magnetic vitrovac amorphous ribbons hasbeen studied using synchrotron radiation. The static magnetization ofthe cluster films in the exchange field of the substrates was measured asa function of coverage using magnetic linear dichroism in the angulardistribution (MLDAD) of the Fe 3p core level photoemission. The switchingdynamics were studied on the nanosecond timescale by time-resolvedspin-polarized photoemission. For a given particle size, the magnetization of theFe cluster film increases with coverage and saturates at a coverage ofabout 0.4 cluster monolayers. Modelling the growth of the magnetizationgives an effective exchange field at the interface of ∼20 T. Densecluster films with several cluster layers have an MLDAD signal at saturation that is∼5%higher than a molecular beam epitaxy (MBE)-grown film, indicating anenhanced spin moment even when clusters are in contact. Coating an exposedsub-monolayer cluster layer with Co increases the Fe MLDAD signal by 35%,indicating a substantially increased magnetic moment within the Fe clusters. Atlow coverages, below the percolation threshold, the switching dynamics of thesample remains the same as in the clean substrate. At around the percolationthreshold, however, a significant acceleration of the magnetic reversal is observedwith a fast component due to a reversal propagating through the cluster film.We show that, on average, each cluster switches in about 10 ns.