T.L. Francis

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.

Large magnetoresistance at room temperature in semiconducting polymer sandwich devices

A thin-film-sandwich device is fabricated consisting of poly(9,9-dioctylfluorenyl-2,7-diyl) sandwiched between two electrodes to study magnetoresistance (MR) effect in semiconducting polymer OLEDs. MR measurements at room temperature for different voltages show that MR traces are independent of the temperature and the angle between film plane and applied magnetic field. However a dependence on the film thickness is observed for an increase in turn-on voltage with increasing film thickness. Hence, MR effect is a bulk rather than an (electrode) interface effect.

Magnetic Field Sensors based on Magnetoresistance Effect in Organic Semiconductor Sandwich Devices

We describe magnetic field sensors based on a recently discovered magnetoresistance (MR) effect in nonmagnetic organic semiconductor sandwich devices. The MR effect reaches up to 10% in a magnetic field of 10 mT at room temperature. We perform an extensive experimental characterization of this effect. We found that the MR effect is only weakly temperature dependent and does not depend on sign and direction of the applied magnetic field. We also measured the device response to alternating magnetic fields up to 100 kHz. To the best of our knowledge, the discovered MR effect is not adequately described by any of the MR mechanisms known to date.

Large Magnetoresistance at Room Temperature in Organic Semiconductor Sandwich Devices

We describe a recently discovered magnetoresistance (MR) effect in semiconducting polymer and small molecule sandwich devices. The MR effect reaches up to 10% in a magnetic field of 10mT at room temperature. This MR effect is therefore amongst the largest of any bulk material. We characterize this effect and discuss its dependence on voltage, film thickness, temperature, electrode materials and (unintentional) impurity concentration in three different organic semiconductors. We found that the MR effect is only weakly temperature dependent and does not depend on sign and direction of the applied magnetic field. To the best of our knowledge, the discovered MR effect is not adequately described by any of the mechanisms known to date.