  We predict very large changes in the room-temperature electroluminescence of
thermally-activated delayed fluorescence organic light emitting diodes near
patterned ferromagnetic films. These effects exceed the changes in a uniform
magnetic field by as much as a factor of two. We describe optimal ferromagnetic
film patterns for enhancing the electroluminescence. A full theory of the
spin-mixing processes in exciplex recombination, and how they are affected by
hyperfine fields, spin-orbit effects, and ferromagnetic fringe field effects is
introduced, and is used to describe the effect of magnetic domain structures on
the luminescence in various regimes. This provides a method of enhancing light
emission rates from exciplexes and also a means of efficiently coupling
information encoded in magnetic domains to organic light emitting diode
emission.
