Graphene nanoring as a tunable source of polarized electrons
  We propose a novel spin filter based on a graphene nanoring fabricated above a ferromagnetic strip. The exchange interaction between the magnetic moments of the ions in the ferromagnet and the electron spin splits the electronic states, and gives rise to spin polarization of the conductance and the total electric current. We demonstrate that both the current and its polarization can be controlled by a side-gate voltage. This opens the possibility to use the proposed device as a tunable source of polarized electrons. 
Javier Mun\'arriz, Francisco Dom\'inguez-Adame, Pedro A. Orellana and   Andrey V. Malyshev
cond-mat.mes-hall