Large magnetoresistance at room-temperature in small molecular weight organic semiconductor sandwich devices

Abstract

We present an extensive study of a large, room temperature negative magnetoresistance (MR) effect in tris-(8-hydroxyquinoline) aluminum sandwich devices in weak magnetic fields. The effect is similar to that previously discovered in polymer devices. We characterize this effect and discuss its dependence on field direction, voltage, temperature, film thickness, and electrode materials. The MR effect reaches almost 10% at fields of approximately 10 mT at room temperature. The effect shows only a weak temperature dependence and is independent of the sign and direction of the magnetic field. Measuring the devices' current-voltage characteristics, we find that the current depends on the voltage through a power-law. We find that the magnetic field changes the prefactor of the power-law, whereas the exponent remains unaffected. We also studied the effect of the magnetic field on the electroluminescence (MEL) of the devices and analyze the relationship between MR and MEL. We find that the largest part of MEL is simply a consequence of a change in device current caused by the MR effect.