The recently discovered giant magnetic anisotropy of single magnetic Co atoms raises the hope of magnetic storage in small clusters. We present a joint experimental and theoretical study of the magnetic anisotropy and the spin dynamics of Fe and Co atoms, dimers, and trimers on Pt(111). Giant anisotropies of individual atoms and clusters as well as lifetimes of the excited states were determined with inelastic scanning tunneling spectroscopy. The short lifetimes due to hybridization-induced electron-electron scattering oppose the magnetic stability provided by the magnetic anisotropies.

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Using spin-polarized scanning tunneling microscopy, the local excitation of magnons in Fe and Co has been studied. A large cross section for magnon excitation was found for bulk Fe samples while for thin Co films on Cu(111) the cross section linearly scales with film thickness. Recording inelastic tunneling spectra with Fe coated W tips in a magnetic field, the magnonic nature of the excitation was proven. Magnon excitation could be detected without the use of a separating insulating layer opening up the possibility to directly study magnons in magnetic nanostructures via spin-polarized currents.

A combined experimental and theoretical study on the inelastic transfer of spin momentum between a spin-polarized tunneling current and a ferromagnetic electrode is presented. Using inelastic tunneling spectroscopy across a vacuum gap at 4 K we show that high-energy magnons are efficiently excited in inelasticscattering events and that the asymmetry of magnon excitation for tunneling into and out of the ferromagnet is proportional to the spin polarization of the tunneling current. We discuss the size of the resulting spin torque and explain the energy distribution of the excited magnons on basis of spin scattering mediated by the itinerant exchange interaction.

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The electronic structure of the single molecule magnet system {M[Fe(L(1))(2)](3)}4CHCl(3) [M=Fe,Cr;L(1)=CH(3)N(CH(2)CH(2)O)(2) (2-)] has been studied using x-ray photoelectron spectroscopy, x-ray-absorption spectroscopy, soft-x-ray emission spectroscopy, as well as theoretical density-functional-based methods. There is a good agreement between theoretical calculations and experimental data. The valence band mainly consists of three bands between 2 and 30 eV. Both theory and experiments show that the top of the valence band is dominated by the hybridization between Fe 3d and O 2p bands. From the shape of the Fe 2p spectra it is argued that Fe in the molecule is most likely in the 2+ charge state. Its neighboring atoms (O,N) exhibit a magnetic polarization yielding effective spin S=52 per iron atom, giving a high-spin state molecule with a total S=5 effective spin for the case of M=Fe.

Investigations of single magnetic atoms on a Pt surface revealed giant magnetic anisotropies. Recently, scanning tunneling microscopy was used to probe single Fe and Co atoms, dimers, and trimers on Pt͑111͒. The magnetic anisotropy and, additionally, the lifetimes of the magnetically excited states were measured by inelastic tunneling spectroscopy. The lifetimes are in the order of femtoseconds due to an effective electron-electron relaxation process caused by the strong hybridization of the impurity states and the substrate. The different lifetimes are explained by the quantum mechanical nature of Fe and Co on Pt͑111͒. The measurements of an Fe dimer show besides the collinear excitation, a noncollinear excitation with two possible decaying channels: spin-flip and non-spin-flip. Thus information on the magnetization dynamics can be extracted from inelastic spectra.

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