  We report on hysteretic organic magnetoresistance (OMAR) in polymeric diodes.
We found that magnitude and lineshape of OMAR depends strongly on the scan
speed of the magnetic field and on the time delay between two successive
measurements. The time-dependent OMAR phenomenon is universal for diodes made
with various polymers. However, the width and magnitude of OMAR varied with the
polymeric material. The suggestive reason for this hysteretic behavior are
trapped carriers, which in presence of a magnetic field changes the
ferromagnetic ground-state of the polymer leading to long spin relaxation time.
These experimental observations are significant for clarification of the OMAR
phenomenon.
