Hybridization-Induced Inversion Of Spin Polarization At Rubrene/Ferromagnetic Cobalt Interface

The formation of hybrid interface states plays a crucial role in spin injection from a ferromagnetic metal into organic semiconductors. Here, we investigate the energy-level alignment and spin-polarized hybrid interface states between cobalt and rubrene using photoemission spectroscopy. We reveal that the presence of charge injection from cobalt to the rubrene molecular layer is determined by XPS and UPS measurements. We also find a spin-polarized interface state between cobalt and rubrene at 0.5 eV below the Fermi level, which can be attributed to chemical interaction between rubrene and Co(001). This hybridization state can induce spin polarization inversion at the rubrene/Co(001) interface as measured by spin-polarized UPS. The spin polarization inversion at the rubrene/Co(001) interface can be interpreted by a Zener exchange-type mechanism. On the basis of these observations, we obtain a deeper understanding of the electronic structure of the rubrene/Co(001) spinterface and show the importance for the quantitative description of rubrene/Co(001)-based organic spintronic devices.