Temperature dependent sign change of the organic magnetoresistance effect

A sign change of the org. magnetoresistance effect is obsd. as a function of temp. There is a large difference in the IV behavior when the sign of the magnetoresistance (MR) is pos. compared to when the sign of the MR is neg., pointing to the possibility that the sign change of the MR is due to a change in the charge transport mechanism. The pos. and neg. MRs show different characteristic field widths B0 in the MR vs. magnetic field curves. Also, the traces with pos. MR show a clear temp. dependence of B0 while no systematic dependence on temp. is seen in the traces with neg. MR. This behavior can be qual. explained by the recently proposed bipolaron model. (c) 2008 American Institute of Physics. [on SciFinder (R)