Understanding Asymmetric Magnetoconductance in OLEDs: the Effects of Gradient Magnetic Fields

Whilst symmetric forms of magnetoconductance (or magnetoresistance) in organic semiconductor devices have been widely observed and modelled over the past two decades, examples of asymmetric magnetoconductance do appear in the literature but have been largely overlooked and their origin has not been explained. Here, we demonstrate that the symmetry of the magnetoconductance can be broken in the presence of a nonlinear gradient magnetic field, especially within the ultra-weak magnetic field range (approximately -300 mu T to +300 mu T). Using a simple numerical model, we demonstrate that this asymmetry in magnetoconductance is sensitive to both the magnitude and direction of the nonlinear gradient magnetic field, and the modelled results are well matched with what has been experimentally observed. This work both explains the origin of the observed asymmetric magnetoconductance and cautions researchers about the potential effect of the nonlinear gradient magnetic fields on the magnetoconductance measurements.