Spin injection from ferromagnetic Co nanoclusters into organic semiconducting polymers

We report a spin-polarized hole injection into organic semiconductor poly[2-methoxy-5-(2(')-ethylhexyloxy)-1,4-phenylenevinylene (MEHPPV) layer from cobalt (Co) nanoscale clusters based on electroluminescence (EL) studies at liquid nitrogen temperature. The magnetic field effect on EL intensity indicates that the spin injection essentially increases the singlet-to-triplet exciton ratio in organic semiconductors. The Co size-dependent EL shows that the spin-injection efficiency decreases rapidly when the Co clusters percolate to a continuous film. The thickness-dependent EL enhancement of magnetic field suggests that the diffusion length of spin-polarized holes is about 60 nm in the MEHPPV.