  A small magnetic field (~30 mT) can effectively modulate the
electroluminescence, conductance and/or photocurrent of organic semiconductor
based devices, up to 10% at room temperature. This organic magnetic field
effect (OMFE) is one of the most unusual phenomena of both organic electronics
and, more basically, magnetism, since all device components are nonmagnetic.
However, in spite of latest surge of research interest, its underlying
mechanism is still hotly debated. Here we experimentally identify that the
magnetic field induced increase of intersystem crossing rate (between either
excitons or polaron pairs), and decrease of triplet exciton-polaron quenching
rate are responsible for the observed OMFEs. The diversity of observed OMFE
results, such as sign change and operating condition dependence, originates
from the difference of devices physics.
