Dr. Sabine Steil, I. Physikalische Institut, Universität Göttingen
One crucial factor determining the performance of spintronic devices, such as GMR or TMR heads, is the magnitude of the spin polarization of the conduction electrons generated in the magnetic electrodes. The value of this spin polarization can be manipulated using spin filter effects after or during the electron injection. Hybrid ferromagnetic metal/organic interfaces can exhibit efficient spin-filtering properties and therefore present a promising class of materials for the future development of new spintronic devices. The hybrid interface between the ferromagnetic metal cobalt and the metalorganic complex tris(8-hydroxyquinolinato)aluminium is considered as the prototypical interface of hybrid organic spintronic devices. To disentangle the microscopic origin of spin filtering, we optically generate a transient spin polarization in a well-defined hybrid interface state that we follow with a spin-resolved real-time pump?probe two-photon photoemission experiment. We find that the electrons are trapped at the interface in a spin-dependent manner for a surprisingly long time of the order of 0.5?1?ps. We conclude that ferromagnetic metal/organic interfaces act as spin filters because electrons are trapped in hybrid interface states by spin-dependent confining potentials.