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Graphene Holds Promise for Spintronics...

Von: Ken Kubos (kubos@execpc.com) [Profil]
Datum: 13.02.2008 23:03
Message-ID: <13r6q8riuajov38@corp.supernews.com>
Newsgroup: uk.rec.ufoalt.ufo.reports

Graphene Holds Promise for Spintronics

Electron spins have been predicted to align along the so-called zigzag edges
of graphene (top). In reality, this perfect order is strongly affected by
thermal excitations, thus imposing strict limitations on graphene-based
spintronic devices. Researchers are studying the theoretical general types
of spin disorder (middle and bottom) in order establish these limitations.
Image credit: Oleg V. Yazyev, EPFL.

Graphene is a nanomaterial which combines a very simple atomic structure
with intriguingly complex and largely unexplored physics. Since its first
isolation about four years ago, researchers suggest a large number of
applications for this material in anticipation of future technological
innovations. Specifically, graphene is considered as a potential candidate
for replacing silicon in future electronic devices.
Theoretical physicists from the Swiss Federal Institute of Technology in
Lausanne (EPFL) and Radboud University of Nijmegen (The Netherlands)
performed a virtual crash-test of graphene as a material for future
spintronic devices. In particular, a possible components of future
computers. The material successfully passed the test, albeit with some
reservations. The results have been published in the February 1, 2008, issue
of Physical Review Letters.

Current technology uses the charge of electrons to operate information in
electronic devices. As an alternative, one can use intrinsic spin of
electrons for this purpose. Electronic devices making use of electron spin
has acquired the term, spintronic devices. Several types of such devices
have already found their way into the market-place in high-capacity hard
drives. Recently it was introduced in a non-volatile magnetic random access
memory (MRAM). Further, replacement of charge-based devices by the
spintronic components promises faster computers and less energy consumption.

While spintronics requires magnetic materials, graphene itself is
non-magnetic. However, when a single graphene layer is cut properly, ( e.g.
using lithographic techniques widely used in the current semiconductor
technology), electron spins are theoretically predicted to align at the
edges of graphene. This amazing property of graphene has attracted
considerable attention by theoretical researchers giving rise to new designs
of spintronic devices.

However, there is a gap between the theoretical models and the actual
prototypes of such devices. The problem lies in the fact that such edge
spins form a truly one-dimensional system. It is known that one-dimensional
systems are very sensitive to thermal disorder which destroys the perfect
arrangement of spins. Strictly speaking, a one-dimensional magnet cannot
maintain the perfect alignment of magnetism at a temperature above absolute
zero. This entropy-driven behavior is in sharp contrast to bulk materials
(such as iron), which is able to keep the perfect order of electron spins
below certain temperatures, (Curie temperature). This factor allows using
bulk materials as permanent magnets. An important component of modern
technology. On graphene edges, the order on spins can exist only within a
certain range which limits the dimensions of spintronic devices.

Researchers from Switzerland and Netherlands performed,
"computer-time-demanding first principles calculations," in order establish
the range of magnetic order at graphene edges. At room temperature, the
range or spin correlation length, was found to be around 1 nanometer which
limits device dimensions to several nanometers. This result may first look
rather disappointing. This is about one order of magnitude below the length
scales of the present-day semiconductor manufacturing processes.
Nevertheless, graphene performed better than any other material when it came
to one-dimension and room temperature factors. In other words, graphene is
the best performer on the nanoscale.

"We are very optimistic about these results," says Oleg Yazyev, Postdoctoral
Researcher at the Swiss Federal Institute of Technology. "One can now devise
different ways of increasing the spin correlation length on graphene edges."
Dr.Yazyev further stated, " For instance, we are now looking for an
appropriate chemical modification of graphene edges in order to further
extend the length-scale limits. This is only beginning of an interesting
direction of research".

Citation: 'Magnetic Correlations at Graphene Edges: Basis for Novel
Spintronics Devices', Physical Review Letters 100, 047209 (2008)
[web-link: http://link.aps.org/abstract/PRL/v100/e047209 ]

Source: EPFL



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