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.

No abstract

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.

No abstract