AVS 49th International Symposium
    Magnetic Interfaces and Nanostructures Thursday Sessions
       Session MI+SS-ThM

Invited Paper MI+SS-ThM7
Magnetism of Adatoms and Clusters

Thursday, November 7, 2002, 10:20 am, Room C-205

Session: Magnetic Spectroscopies
Presenter: P. Gambardella, Ecole Polytechnique Fédérale de Lausanne, Switzerland
Correspondent: Click to Email
In the last ten years, x-ray magnetic circular dichroism (XMCD) has found widespread application as an element-specific magnetometry tool in the study of magnetic thin films. Here we show that x-ray absorption spectroscopy (XAS) and XMCD can be successfully employed to probe diluted transition-metal systems with surface impurity concentration as low as 3 x 10@super 12@ atoms cm@super -2@, thus leading to the direct characterization of the electronic and magnetic configuration of impurity systems as well as supported nanostructures. Combined XAS-XMCD provide simultaneous information about the the d-valence state and related spin and orbital moment of transition-metal atoms that is not accessible by traditional techniques such as, e.g., magnetic susceptibility, resistivity, and electron paramagnetic resonance measurements. A first fundamental issue is how the magnetic moment of surface adatoms depends on the interaction with the host conduction electrons. We show that Fe, Co, and Ni, owing to d-electron localization, display large spin and orbital moments on low electron density simple-metal substrates which are progressively quenched as the surface electron densitiy increases.@footnote 1@ A second fundamental issue is how the interaction with the substrate and adjacent adatoms influnces the magnetic anisotropy of the system. We report giant magnetic anisotropy values up to 3.3 meV/atom for Co clusters and atomic wires on Pt surfaces. A clear correlation is established between the atomic coordination, the magnitude of the orbital moment and the anisotropy energy, with implications for magnetic ordering phenomena.@footnote 2@ @FootnoteText@ @footnote 1@ P. Gambardella et al., Phys. Rev. Lett. 88, 047202 (2002).@footnote 2@ P. Gambardella et al., Nature 416, 301 (2002).