Magnetoresistance in magnetic tunnel junctions with an organic barrier and an MgO spin filter

Exchange-biased magnetic tunnel junctions with a CoFeB/MgO pinned layer, a Co free layer and an aluminum tris-(8-hydroxyquinoline) spacer layer of thickness ranging from 0–8 nm have been prepared by photolithography. The devices show a room-temperature, zero-bias magnetoresistance of $12.5\pm 0.3\%$ , which is unchanged after the crossover from tunneling to hopping transport at a barrier thickness of about 4 nm. The spin-diffusion length in the hopping regime is much greater than 10 nm. The magnetoresistance in the tunneling regime changes sign at a positive bias of 250 mV, and it is maximum at −100 mV.