Doping of organic semiconductors (OSCs) has proven to be an efficient strategy to adjust their electronic properties for implementation in organic-based electronic devices. The recent success in the application of OSCs for spintronics applications raises the fundamental question if doping can be used as well to tailor the spin properties of OSCs, thus enhancing their performance in spintronics devices. In this contribution, we will first introduce a recently developed purpose-made technique based on spin resolved two-photon photoemission [1]. It allows obtaining direct and quantitative information about interfacial effects on spin-injection and on the spin transport properties of OSCs, as it has been demonstrated for the model system consisting of the interface between the ferromagnet cobalt and the OSC copper phthalocyanine (CuPc). In a further step, we have studied the influence of alkali metal doping on the spin properties of the cobalt/CuPc interface. We show that doping of CuPc with caesium or natrium atoms allows to achieve enhanced spin injection efficiency across the FM/OSC interface and to obtain quasi-elastic spin-flip lengths in the OSC of up to 50 nm at room temperature, a factor of five higher than the values obtained without doping [1]. These observations indicate the suitability of doping for an effective tuning of the spin properties of organic-based spintronics devices.

[1] M. Cinchetti et al., Nature Materials 8, 115-119 (2009)

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1. Spin polarization at a Co₂MnSi/MgO interface studied by spin resolved photoemission
2. Investigations of metallo-phthalocyanines grown on ferromagnetic Co((001) thin films.