Magnetoresistance in an all-organic-based spin valve

We demonstrate spin injection and detection in an all-organic-based magnetic tunnel junction using two layers of organic-based magnet V[TCNE]$_x$ (x$\sim$2, TCNE: tetracyanoethylene) as the magnetic contacts and organic semiconductor rubrene (C$_{42}$H$_{28}$) as the spacer. For the V[TCNE]$_x$ film growth, we exploited two different growth techniques, chemical vapor deposition and molecular layer deposition, which result in different coercivities of V[TCNE]$_x$ films. The spin valve devices show negative magnetoresistance (MR), the sign of which does not change with temperature and bias. To explain the unusual negative MR, we propose a simple phenomenological bias-enhanced selective tunneling (BEST) model based on the different spin polarizations of the molecular energy levels of V[TCNE]$_x$. Our results show the significance of bias induced energy level shift in organic spintronic devices due to relatively narrow spin polarized bandwidths. This work was supported in part by AFOSR Grant No. FA9550-06-1-0175, DOE Grant Nos DE-FG02-01ER45931, DE-FG02-86ER45271, NSF Grant No. DMR-0805220, the Center for Emergent Materials (an NSF-MRSEC; Award Number DMR-0820414) at The Ohio State University and the Institute for Materials Research at The Ohio State University.