| The development of spintronics needs to find the possibility of efficient spin manipulation and promising materials for spin transportation. Graphene as a promising material for future spintronics devices has attracted extensive attention recently. Most fascinating properties of graphene such as Klein tunneling, half-integer quantum-Hall effect, and finite minimum of conductivity, arise from the chirality of charge carriers and the gapless linear spectrum near the Dirac points.The electronic properties of graphene can be tuned not only by external electric fields and magnetic barriers, but also by mechanical strains. The mechanical strains shift the Dirac cones away from the points K and K'in opposite directions. The lattice deformation with a long wavelength acts on the Dirac fermions as a pseudomagnetic field. Thus a local strain can generate a transport gap in the transmission spectrum. On the other hand, the orbital inequivalence of the Dirac points K and K'provides a twofold valley degree of freedom, which might be utilized to design valley electronic devices with spintronic analogies. It has been demonstrated experimentally spin injection and detection in graphene sheets and observed a spin coherence length above 1 micron at room temperature.We investigate spin-dependent electronic transport through normal/strained/normal/ferro-magnetic/normal graphene junctions. The substrate strain leads to opposite shifts of the K and K'valleys and thus modulates the orbital motion of Dirac electrons. Since this effect is sensitive to the incident energy, a train-tunable spin current can be achieved when allowed incident energy dependent on spin. The transmission of such a junction is both valley-resolved and spin-resolved. However, the conductance is only spin-polarized. The spin polarization can be tuned by the strain strength as well as electrostatic potentials. This device provides an alternative routine to manipulating electron spins in graphene without magnetic fields.
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