Elucidation of spin state of conduction electrons in graphene

Elucidation of spin state of
conduction electrons in graphene

When a low velocity spin-polarized
metastable He beam is irradiated on
the specimen surface, the He atoms
rebound above the surface without
penetrating to the interior. As a
result, it is possible to selectively
detect surface information. During
the collision, the 1s-hole (black
broken line arrow) is filled by a
surface electron and the He atom
returns to its ground state by
releasing the 2s electron. Since the
surface electron filing the 1s-hole
should have the same spin to the
hole, the ejected electron carries the
spin information of surface electrons.
By aligning the spin direction of 1s-
hole a metastable He becomes a spin
detector. In the present study the
spin state of topmost layer of
graphene/Ni(111), namely graphene,
has been selectively detected with
this method.
Using a spin-polarized metastable
helium beam, a group headed by Dr.
Shiro Entani, who is a limited-term
researcher at the Advanced Science
Research Center, Japan Atomic
Energy Agency (President: Shojiro
Matsuura) and Dr. Yasushi Yamauchi,
a Group Leader in the Nano
Characterization Unit, National
Institute for Materials Science
(President: Sukekatsu Ushioda)
succeeded in detecting the electronic
spin state of only the graphene
contacted to a magnetic metal in
devices.
Graphene is considered a promising
substrate material for next-
generation spintronics, as it
possesses many properties that are
suitable for transmission of electronic
spin information. In order to utilize
graphene in spin devices, techniques
for controlling its spin state are
indispensable, and among these, the
development of a spin injection
technique using a magnetic electrode
is a key issue. In developing these
techniques, first, it is necessary to
know the spin state of the graphene
which is contacted to the magnetic
metal electrode . It was difficult,
however, for conventional techniques
to selectively obtain the spin
information of the graphene because
the weak signal from the graphene,
which comprises a single atomic
layer , is buried in the strong signal
from the magnetic substrate.
In this study, the JAEA-NIMS research
group succeeded for the first time in
observing the electronic spin state of
only the graphene by measuring a
junction of graphene and magnetic
metal (nickel) with a spin-polarized
metastable helium (He) beam. The
results revealed that, in conduction
electrons of graphene contacted to
nickel, spin polarization occurs with
the same orientation as the spin of
the nickel.
This research achievement is
expected to greatly advance research
on the spin properties of various 2-
dimensional materials including
graphene which are a focus of
attention as new spintronics
materials, as well as device
applications such as development of
spin injection techniques, etc.
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