https://doi.org/10.1007/s100530170089
Synchrotron radiation studies of mass-selected Fe nanoclusters deposited in situ
1
Department of Physics and Astronomy, University of
Leicester, Leicester LE1 7RH, UK
2
ESRF, BP 220, F-38043 Grenoble Cedex, France
Corresponding author: a cb12@le.ac.uk
Received:
14
December
2000
Published online: 15 September 2001
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 
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 Å (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.
PACS: 75.50.Tt – Fine-particle systems; nanocrystalline materials
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2001
