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Magnetismus Poster: Do., 13:00–15:30 D-P240
Magnetic properties of small, mass selected metal clusters
Michael Martins 1 , Leif Glaser 1 , Matthias Reif 1 , Sebastian Hankemeier 1 ,
Wilfried Wurth 1
1 Insitut für Experimentalphysik, Universität Hamburg, Luruper Chaussee 149, D-
22761 Hamburg
Size selected transition metal cluster allow to study the transition of the magnetic
properties as a function of cluster size. Regarding possible applications these clusters
have to be supported on a substrate or embedded in a matrix, where cluster-support
interaction will influence their physical properties. To investigate the magnetic properties
of such deposited clusters, x-ray magnetic circular dichroism (XMCD) is an ideal
tool, due to its element selectivity and the capability to measure spin- and orbital
moments independently. For iron cluster deposited on a remanently magnetized thin
nickel film a strong size dependence of the spin- and orbital moments have been found
[1,2].
The magnetic properties of the deposited clusters might be strongly influenced by
the surface material. Thus, we have studied the magnetic properties of deposited,
mass selected Crn and Run clusters on thin iron and nickel films. Crn clusters are of
special interest, due to the anti-ferromagnetic coupling of chromium in the bulk. For
Run-clusters in the gas phase a super-paramagnetic coupling is found, whereas this 4d
element is non-magnetic in the bulk.
Due to the anti-ferromagnetic coupling of Cr a complicated coupling scheme of the
magnetic moments can be expected, e.g. already in a trimer for the third atom the spin
will be frustated [3]. Thus we have started studies on chromium clusters in the size
range from n=1 to n=13 deposited on ultrathin ferromagnetic nickel and iron films.
Whereas for Cr cluster on Ni films no XMCD signal is found, Cr clusters on Fe films
show a strong decrease of the magnetic moment by a factor of 4 with increasing cluster
size. This effect can be interpreted in terms of a non-collinear coupling of the magnetic
moments within the cluster and relative to the surface [4].
For Run clusters we have performed experiments on deposited atoms and dimers on Ni
and Fe surfaces. XMCD-experiments on the 4d elements are much harder to perform,
due to the small cross section of the M2,3 edges as compared to the corresponding L2,3
edges of the 3d metals. Whereas for Ru atoms on Ni(100) a ferromagnetic coupling is
found, the Ru dimer on Ni(100) is non-magnetic. For Ru1,2 on a Fe surface the inverse
behavior is found.
[1] J.T. Lau, A. Föhlisch, R. Nietubyc, M. Reif, W. Wurth, Phys.Rev.Lett.89 (2002)
057202
[2] J.T. Lau, A. Föhlisch, M. Martins, R. Nietubyc, M. Reif, W. Wurth, New J. Phys.
4 (2002) 98.1
[3] T. Jamneala, V. Madhavan, M.F. Crommie, Phys. Rev. Lett. 87 (2001) 256804
[4] M. Reif, L. Glaser, M. Martins, W. Wurth, S. Lounis, S. Blügel, in preparation