The effect of a copper interfacial layer on spin injection from ferromagnet to graphene

Abstract

Aiming at enhancing the spin-injection efficiency from ferromagnet to graphene, graphene-based spin valve devices with ferromagnet–Cu–graphene contacts have been fabricated and studied. The ferromagnet–Cu–graphene contact has attracted our attention because of the spin-preserving characteristic of ferromagnet–Cu interface and possible presence of moderate potential barrier at the Cu–graphene interface. The latter may help to alleviate the conductance mismatch issue in spin injection from ferromagnet to graphene. Devices with or without Cu interfacial layers have been fabricated by both evaporation and sputtering on mechanically exfoliated graphene sheets. A potential barrier of 33 meV was derived for the Cu–graphene interface in evaporation-deposited devices from the temperature-dependence of contact resistance. On the other hand, pure ferromagnet–graphene contact exhibits a much lower contact resistance due to its chemisorption interface with graphene. Nonlocal magnetoresistance measurements showed a moderate enhancement of spin injection efficiency with the aid of the Cu interfacial layer.