Interlayer dependent polarity of magnetoresistance in graphene spin valves

Abstract

We fabricated spin valves of NiFe/Al₂O₃/single layer graphene (SLG)/Co, NiFe/SLG/Co, and NiFe/Al₂O₃/Co. In the fabrication, lithography processes using e-beam resist or photoresist were avoided to obtain residue-free clean junctions in all devices. While all three types of magnetic junctions showed a distinctly clear spin valve effect from 10 to 300 K, the polarity of magnetoresistance (MR) revealed different signs. A negative MR value (−1.6% at 10 K) was observed in the spin valve effect for the junction with the Al₂O₃/SLG interlayer, however the other types of junctions showed conventional positive MR values. The positive or negative MR signs are explained by the Julliere model of spin-dependent tunneling.