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news release:
New magnetic polymers may advance
spintronics technologies
Argonne, IL, December 15: Researchers at
the U.S. Department of Energy's Argonne National Laboratory have pioneered a new
approach for making magnetic polymers that are held together with very strong
hydrogen bonds. These polymers contain an innovative bifluoride, HF2–,
building block that allows a magnetically ordered state to be obtained. The
development may help lead to new techniques for faster and more versatile
computer chips, among other applications.
The research is reported in the December 21 issue
of
Chemical Communications and is featured on the cover of the journal.
The research examines the role of hydrogen bonds
in designing the structure of molecular materials. “Nature uses hydrogen bonds
to do all kinds of things, including holding the DNA double helix together, and
is important in a wide range of biological processes,” said John Schlueter,
Argonne chemist and an author of the research paper. “When making molecular
materials, strong bonds are needed to fabricate the molecular building blocks.
Weaker bonds, including hydrogen bonds, act as the glue to hold the blocks
together.” It's this phenomenon that allowed the creation of the first fully
organic superconductor, discovered at Argonne a decade ago.
The magnetic polymer, which forms as beautiful
deep blue crystals, is produced when copper ions bind to pyrazine molecules,
creating a sheet-like structure. Like a Tinkertoy® building block, the
bifluoride ion acts as a bridge to hold the planes together. The product is a
three-dimensional coordination polymer, which forms through very mild synthetic
conditions.
The exceptionally simple structure is held
together by one of the strongest hydrogen bonds known, making this a very
thermally stable material. Each copper ion, which sits at the corner of a
molecular cube, contains one unpaired electron. These spins are disordered at
normal temperatures, a state known as paramagnetism; however, the spins begin to
align in opposite directions as the temperature drops, creating a magnetic state
called antiferromagnetism.
The researchers studied the magnetic properties
of the material by a technique that uses muons as mini-magnetometers. Muons are
subatomic particles that are heavier than electrons but have the same charge and
magnetic spin. The researchers hope that the magnetic studies will help them
understand to what extent bifluoride units and their hydrogen bonds influence
the spin arrangement on neighboring magnetic centers.
This work has demonstrated for the first time
that this innovative molecular building block can be rationally incorporated
into molecular frameworks under mild synthetic conditions and that magnetic
superexchange can indeed be mediated through hydrogen bonding. The ingenious
synthesis of the novel 3-D coordination polymers opens up a route to a range of
new solid state coordination compounds that will provide a way to study the how
the unique properties of hydrogen bonds can be used to modify the spin
arrangement of neighboring magnetic centers. One next step, Schlueter said, is
to change the spacing between the layers of the compound to see what impact that
has on the nature of the bond and how that affects the magnetic properties of
the material.
In the past, this group has pioneered a new
process for the synthesis of molecular superconductors, discovering the most
highly tunable family known and the first completely organic superconductor.
They have shown that hydrogen bonding is important for superconductivity in
these materials because it intimately links the conducting sheets to the anionic
layers. Schlueter is now interested in making hybrid materials by inserting
magnetic layers between the conducing sheets to form a simple spintronic device.
To accomplish this, it is critical to understand how the conducting and magnetic
layers communicate through hydrogen bonds.
Spintronics, also known as spin electronics, is
an emerging technology that looks to develop devices that exploit the quirky
world of quantum physics, or physics at the incredibly small atomic level,
particularly the up-or-down spin property of electrons. While conventional
electronics use the charge of the electron, spintronic devices would use both
the spin and charge, achieving vastly superior performance. Scientists across
the globe are racing to develop the spintronics field. It could revolutionize
the computing industry with chips that are more versatile and exponentially more
powerful than today's most cutting-edge technology.
Schlueter did the research in collaboration with
a former Argonne postdoctoral researcher, Jamie Manson, who is now at
Eastern Washington
University, and with colleagues at
Oxford University, the
High
Field Magnet Laboratory in Dresden, Germany, and
North Carolina State University.
This research was funded by DOE's Office of
Science, Office of
Basic
Energy Sciences' Division of
Materials
Sciences and Engineering.
The nation's first national laboratory, Argonne
National Laboratory conducts basic and applied scientific research across a wide
spectrum of disciplines, ranging from high-energy physics to climatology and
biotechnology. Argonne is managed by
UChicago Argonne,
LLC for the U.S. Department
of Energy 's Office of
Science.
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