  The understanding of magnetoresistance (MR) in organic spin valves (OSVs)
based on molecular semiconductors is still incomplete after its demonstration
more than a decade ago. While carrier concentration may play an essential role
in spin transport in these devices, direct experimental evidence of its
importance is lacking. We probed the role of charge carrier concentration by
studying the interplay between MR and multilevel resistive switching in OSVs.
The present work demonstrates that all salient features of these devices,
particularly the intimate correlation between MR and resistance, can be
accounted for by the impurity band model, based on oxygen migration. Finally,
we highlight the critical importance of carrier concentration in determining
spin transport and MR in OSVs and the role of interface-mediated oxygen
migration in controlling the OSVs response.
