Magnetic excitations of small magnetic clusters and single atoms

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Inelastic scanning tunneling spectroscopy (ISTS) has proven to be an excellent tool for the investigation of magnetic excitations in nanostructures allowing both to determine the excitation spectrum [1, 2, 3] and the life times of the excited states [4, 5]. Microscopically, the interplay of spin-orbit interaction and the crystal field causes a local magnetocrystalline anisotropy energy (MAE), i.e. an energy that depends on the direction of the net magnetic moment. This lifts the degeneracy of the magnetic multiplet of the atom or cluster and can be probed in a spin excitation experiment. In clusters, also non-collinear spin states can be excited, in which the moments of individual atoms are turned with respect to each other with the additional cost of the exchange energy. The life time of the excited state is mainly determined by an electronic relaxation process, in which the energy of the excited state is given to a conduction electron of the substrate [4, 5, 6]. Further the MAE induces mixing within the magnetic multiplet in accord to the Stenvens operators enabling tunneling of the magnetization. For magnetic transition elements, large anisotropies of the order of 10 meV per atom could be observed [7, 2, 8]. Due to the effective coupling of the atomic 3d states to the substrate, be it metallic [2, 6] or a thin insulating layer [5], the life times of the excited and ground states are between 10−14 and 10−7s, and no stable magnetic states could be achieved. In this proposal, we will work on 4f metallic atoms in which the magnetic moment is strongly located in the 4f orbitals such that the hybridization to the surrounding states is significantly reduced. This way, stable spins can be achieved for longer time scales that allow to investigate their quantum nature and to perform simple quantum computational operations.