Unravelling the role of the interface for spin injection into organic semiconductors

Organic materials are attractive for building spintronics devices owing to their expected long spin lifetimes. Moreover, the ability to control their properties by changing their composition and molecular structure makes them easier to tailor to given tasks than inorganic materials. However, most studies of candidate organic spintronics materials focus on their bulk spin transport characteristics. Here we investigate the equally important process of spin injection and how it is influenced by interface coupling in the prototype organic semiconductor, Alq(3). We fabricate nanometre-scale (La, Sr) MnO(3)/Alq(3)/Co magnetic tunnel junctions that exhibit a magnetoresistive response of up to 300%. Furthermore, we develop a spin transport model that describes the role of interfacial spin-dependent metal/molecule hybridization on the effective polarization allowing enhancement and even sign reversal of injected spins. We expect such insights to lead towards the molecular-level engineering of metal/organic interfaces to tailor spin injection and bring new electrical functionalities to spintronics devices.