Magnetism and magnetic transport properties of the polycrystalline
graphene nanoribbon heterojunctions
D. Wang, Z.H. Zhang
*
, X.Q. Deng, Z.Q. Fan, G.P. Tang
School of Physics and Electronic Science, Changsha University of Science and Technology, Changsha 410114, China
article info
Article history:
Received 26 August 2015
Received in revised form
11 October 2015
Accepted 28 October 2015
Available online 3 November 2015
abstract
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 nano-
ribbons (PGNRs) with a zigzagearmchairezigzag structure are investigated systematically. It shows that
GBs can induce significant localize d electron states and magnetic ordering in the region consisting of GBs
and armchair segment, and t he 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.
© 2015 Elsev ier Ltd. All rights reserved.
1. Introduction
Graphene, one kind of two-dimensional (2D) layered crystal
material, have attracted an extensive research interest in recent
years due to its very promising features in electronics [1e3].
However, an ideal graphene sheet with infinite long-range order for
carbon atoms is lacking of an electronic band gap [1], which will
inevitably limit its realistic applications in future electronic devices.
To solve this issue, one typical method is to cut a graphene
sheet along certain crystallographic directions by the patterning
technology [4] to form various differently shaped graphene struc-
tures, including zigzag-edged and armchair-edged graphene
nanoribbons (ZGNRs and AGNRs) [5], graphene nanoflakes [6],
antidot structures [7], and so on. Numerous studies have shown
that electromagnetic properties of these graphene structures are
individually distinctive. Among such geometrical structures, ZGNRs
are the most prominent species due to featuring a unique electrical
quality and magnetic properties, and it is believed that their mag-
netic zigzag edges would be a basis for novel magnetic devices.
Therefore, magnetic devices based on perfect ZGNRs have been
intensively investigated to date [8e12].
However, in fact, the realistic graphene is usually a poly-
crystalline structure as most of materials due to intrinsic topolog-
ical defects originating generally from the growth process.
Typically, imperfections and kinetic factors of the substrate make a
rotation of the topmost layer on the graphite substrate [13], leading
to multiple domains appearing with different crystallographic
orientations and grain boundaries (GBs) inside graphene [14e16].
Graphite, a precursor to produce graphene by exfoliation, has GBs
with pentagoneheptagon line defects, so that they can change the
geometrical chirality to form zigzag-and armchair-edge coexisting
structures, which was proposed first by Terrones et al. [17] and
observed experimentally later by scanning tunneling micro-
scopy(STM) in highly ordered pyrolytic graphite (HOPG) [18,19].So
far, universal existence of GBs in graphene have also been
confirmed in the transmission electron microscopy (TEM) and op-
tical microscopy measurements [20,21]. Recently, Lahiri, et al. [22]
reported that structurally well-defined one-dimensional topologi-
cal defect could be controllably introduced in epitaxial graphene,
and found that such defects would yield a pronounced perturbation
into the electronic structure. Undoubtedly, the domain size and the
creation of localized electronic state upon a defect line will affect
* Corresponding author.
E-mail address: lgzzhang@sohu.com (Z.H. Zhang).
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Carbon
journal homepage: www.elsevier.com/locate/carbon
http://dx.doi.org/10.1016/j.carbon.2015.10.090
0008-6223/© 2015 Elsevier Ltd. All rights reserved.
Carbon 98 (2016) 204e212