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

TL;DR

This paper reports a significant room-temperature negative magnetoresistance effect in small molecular weight organic semiconductor devices, with nearly 10% change at low magnetic fields, and explores its dependence on various parameters and its relation to electroluminescence.

Contribution

It is the first detailed characterization of large magnetoresistance in small molecule organic devices at room temperature, including its dependence on multiple factors and its connection to electroluminescence.

Findings

MR reaches nearly 10% at 10 mT at room temperature

MR effect is weakly temperature-dependent and field-direction independent

Magnetic field affects the power-law prefactor of current-voltage characteristics

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.