On the Mechanism Causing Large Room-Temperature Magnetoresistance in OLEDs

We report on the experimental study of a recently discovered, large room-temperature magnetoresistance effect in sandwich devices comprised of nonmagnetic electrodes and various organic semiconductor thin films. The effect reaches up to 10{\%} in a magnetic field of 10 mT at room temperature and saturates at fields larger than several tens of milliTeslas. In materials with strong spin-orbit coupling the characteristic magnetic field scale shifts to fields that are 10-100 times larger, consistent with the spin-orbit coupling strength. Our experiments therefore show that the organic magnetorestive effect is caused by spin-dynamics, possibly induced by the hyperfine interaction. We discuss two recently proposed models to explain the organic magnetorestive effect, which are based on spin-dependent exciton formation and spin-dependent hopping, respectively.