Magnetism and magnetic transport properties of the polycrystalline graphene nanoribbon heterojunctions

The polycrystalline structures for graphene are practically unavoidable by the currently existing growth routes, thus the scattering issue of electrons by grain boundary (GBs) becomes a theoretical and an experimental relevant one. Here, magnetic transport properties of the polycrystalline graphene nanoribbons (PGNRs) with a zigzag-armchair-zigzag structure are investigated systematically. It shows that GBs can induce significant localized electron states and magnetic ordering in the region consisting of GBs and armchair segment, and the interdomain electronic transmission across the GBs is transparent or blocked completely depending on the spin direction (a or b) of electrons as well as the microscopic details and relative orientation of GBs, which causes a special spin polarization for the magnetic transport. Especially, the perfect spin-filtering, spin-rectifying, and giant magnetoresistance effects can be realized simultaneously in such heterojunctions. These novel features can be rationalized by the spin splitting of molecular levels as well as the delocalization degree and parity limitation of molecular orbital wave functions in the scattering region serving as an extended molecule. Also shown is that PGNR-based heterojunctions possess a large range of magnetic behaviors with variation of its geometrical size. (C) 2015 Elsevier Ltd. All rights reserved.