The magnetoresistance (MR) of Co/multilayer graphene/Co spin valve structures has been studied. A positive MR of up to 0.39% at 2 K with switching at magnetic fields that are consistent with the magnetization orientations inferred from anisotropic MR data obtained for the Co contacts has been observed. The positive MR decreases with increasing excitation current and eventually changes sign. The positive MR decreases with increasing temperature, but the negative MR has no temperature dependence.
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The authors were grateful to Daniel C. Frisbie for useful advice. This work was supported by the National Science Foundation through the University of Minnesota Materials Research Science and Engineering Center under Grant No. NSF/DMR-0212032.