Electronic Transport Through A Grapheme-based Ferromagnetic/Grapheme Nanoribbon/Ferromagnetic Junction

In this paper，we investigated the electronic transport property through a grapheme-basedferromagnetic/grapheme nanoribbon(GNR)/ferromagnetic junction by using the Green’sfunction technique and Landauer-Büttiker formalism. We calculated the conductance,magnetoresistance and spin polarization in the following scattering region: perfect andcontractive zigzag grapheme nanoribbon(ZGNR), perfect and contractive armchair graphemenanoribbon(AGNR), respectively.It is found that the spin-dependent conductance emerges zero conductance plateau whenN（the witdh of the perfect zigzag graphene nanoribbon）is even, and the conductance has awider zero conductance plateau in the antiparallel configurations. The100%magnetoresistance (MR) plateau and the100%(-100%) spin polarization plateau emergesaround zero Fermi energy. If the scattering region has a contraction, the conductance issuppressed, however, the value of the MR and the spin polarization is enhanced when theFermi energy outside the region of （-0.2t,0.2t）, meanwhile, an inversion appears aroundzero Fermi energy.The conductance in the antiparallel configurations shows zero conductance plateau andthe conductance in the parallel configurations is always large than1.5e2/hwhen N is odd.The zero conductance plateau in the antiparallel configurations remains to be unchangedwhen the scattering region has a contraction, but the conductance oscillation disappeared inthe parallel configurations. Meanwhile, the conductance of the system is enhanced ordecreased in some Fermi energy region. The100%magnetoresistance plateau emerges aroundzero Fermi energy and its width remains to be unchanged with the contracting of thescattering region and the value of the spin polarization has not changed significantly.Comparing to the case of the perfect armchair-edge grapheme nanoribbon which width isequal to3m (m is an integer), the conductance gets smaller and the zero conductance plateaubecomes wider when the scattering region has a contraction. In addition, the100%MRplateau and the100%(-100%) spin polarization plateau becomes wider.The conductance is equal to zero except some Fermi energy region comparing for the case of the perfect armchair-edge grapheme nanoribbon which width is equal to3m+2, andthe value of the MR is enhanced from60%to100%, the value of the spin polarizationbecomes-100%.