Large magnetoresistance at room temperature in organic semiconductor devices

We describe a large magnetoresistance (MR) effect in organic light-emitting diodes that reaches up to 10% at fields of 10 mT at room temperature. This MR effect occurs both in /spl pi/-conjugated polymers and small molecules. Our devices do not contain any magnetic materials. We found that the MR effect is only weakly temperature dependent and does not depend on sign and direction of the applied magnetic field. This is a novel type of MR-yet to be explained theoretically-that does not have, to the best of our knowledge, an analog in inorganic semiconductor devices.