Synchrotron radiation studies of mass-selected Fe nanoclusters deposited in situ |
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Authors: | C Binns SH Baker MJ Maher SC Thornton S Louch SS Dhesi NB Brookes |
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Institution: | (1) Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK, GB;(2) ESRF, BP 220, F-38043 Grenoble Cedex, France, FR |
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Abstract: | A portable UHV-compatible gas aggregation cluster source, capable of depositing clean mass-selected nanoclusters in situ, has been used at synchrotron radiation facilities to study the magnetic behaviour of exposed and Co-coated Fe clusters in
the size range 250 to 540 atoms. X-ray magnetic circular dichroism (XMCD) studies of isolated and exposed 250-atom clusters
show a 10% enhancement in the spin magnetic moment and a 75% enhancement in the orbital magnetic moment relative to bulk Fe.
The spin moment monotonically approaches the bulk value with increasing cluster size but the orbital moment does not measurably
decay till the cluster size is above ∼ 400 atoms. The total magnetic moments for the supported particles though higher than
the bulk value are less than those measured in free clusters. Coating the deposited particles with Co in situ increases the spin moment by a further 10% producing a total moment per atom close to the free cluster value. At low coverages
the deposited clusters are super-paramagnetic at temperatures above 10 K but a magnetic remanence at higher temperature emerges
as the cluster density increases and for cluster films with a thickness greater than 50 ?(i.e. 2-3 layers of clusters) the remanence becomes greater than that of an Fe film of the same thickness produced by a conventional
deposition source. Thick cluster-assembled film show a strong in-plane anisotropy.
Received 14 December 2000 |
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Keywords: | PACS 75 50 Tt Fine-particle systems nanocrystalline materials |
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