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Science 16 May 2003:
Vol. 300. no. 5622, pp. 1130 - 1133
DOI: 10.1126/science.1082857
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Reports

Giant Magnetic Anisotropy of Single Cobalt Atoms and Nanoparticles

P. Gambardella,1,2* S. Rusponi,1,2 M. Veronese,3 S. S. Dhesi,4{dagger} C. Grazioli,3 A. Dallmeyer,5 I. Cabria,5 R. Zeller,5 P. H. Dederichs,5 K. Kern,1,2 C. Carbone,3,5 H. Brune1

The isotropic magnetic moment of a free atom is shown to develop giant magnetic anisotropy energy due to symmetry reduction at an atomically ordered surface. Single cobalt atoms deposited onto platinum (111) are found to have a magnetic anisotropy energy of 9 millielectron volts per atom arising from the combination of unquenched orbital moments (1.1 Bohr magnetons) and strong spin-orbit coupling induced by the platinum substrate. By assembling cobalt nanoparticles containing up to 40 atoms, the magnetic anisotropy energy is further shown to be dependent on single-atom coordination changes. These results confirm theoretical predictions and are of fundamental value to understanding how magnetic anisotropy develops in finite-sized magnetic particles.

1 Institut de Physique des Nanostructures, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland.
2 Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, D-70569 Stuttgart, Germany.
3 Istituto di Struttura della Materia, Consiglio Nazionale delle Ricerche, Area Science Park, I-34012 Trieste, Italy.
4 European Synchrotron Radiation Facility, BP 220, F-38043 Grenoble, France.
5 Institut für Festkörperforschung, Forschungszentrum Jülich, D-52425 Jülich, Germany.



{dagger} Present address: Diamond Light Source, Rutherford Appleton Laboratory, Didcot OX11 0QX, UK.

* To whom correspondence should be addressed. E-mail: pietro.gambardella{at}epfl.ch

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