No abstract

Random hyperfine fields are essential to mechanisms of low-field magnetoresistance in organic semiconductors. Recent experiments have shown that another type of random field -fringe fields due to a nearby ferromagnet -can also dramatically affect the magnetoresistance. A theoretical analysis of the effect of these fringe fields is challenging, as the fringe field magnitudes and their correlation lengths are orders of magnitude larger than that of the hyperfine couplings. We extend a recent theory of organic magnetoresistance to calculate the magnetoresistance with both hyperfine and fringe fields present. This theory describes several key features of the experimental fringe-field magnetoresistance, including the applied fields where the magnetoresistance reaches extrema, the applied field range of large magnetoresistance effects from the fringe fields, and the sign of the effect.

No abstract

One contribution of 11 to a discussion meeting issue 'Organic semiconductor spintronics: utilizing triplet excitons in organic electronics' .

Recent work has shown that weak applied magnetic fields of several tens of mT can lead to a change of several percent in the (photo)conductivity of organic semiconductor devices. However, it remains to be determined whether the applied magnetic field modifies the (photo)carrier density, their mobility or both. We use magneticfield-dependent time-of-flight spectroscopy to disentangle these two possibilities. We find evidence that the magnetic field leads to a decrease in the photocarrier time-of-flight. We also examine organic magnetoresistive devices in the frequency domain to complete the characterization of the time-dependent field-effect response.