Generation of large spin currents in graphene using adiabatic quantum pumping

We study adiabatic quantum pumping of Dirac fermions in a monolayer graphene in the large pumping amplitude regime in order to study how to generate a large spin polarized current. Spin current is generated by applying two periodic oscillating gate voltages to a monolayer graphene with exchange splitting induced by ferromagnetic proximity. We find that pumped charge and spin currents are sensitive functions of the Fermi energy and pure spin current and spin current with different degrees of polarization and large magnitudes are obtained in our scheme. We also study the effects of parameters of the system, such as the barrier separation and the exchange splitting, on the pumped currents. The spin current generated by this method can be as high as 80-100 nA. This shows the method can be used in the study of spin physics in graphene and the realization of graphene spintronic devices.