Powerful Superconductor in a Class All Its Own
Superconductivity has perplexed,
astounded and inspired scientists ever since it was discovered in 1911. Now, in
the latest of a century of surprises, researchers at the National High Magnetic
Field Laboratory at Florida State University have discovered unusual properties
in a novel superconducting material that point to an entirely new kind of
Frank Hunte, a postdoctoral associate at the lab's Applied Superconductivity
Center (ASC), working with David Larbalestier, Alex Gurevich and Jan Jaroszynski,
and colleagues in David Mandrus' group at Oak Ridge National Laboratory in
Tennessee, discovered surprising magnetic properties in the new superconductors
that suggest they may have very powerful applications -- from improved MRI
machines and research magnets to a new generation of superconducting electric
motors, generators and power transmission lines. The research also adds to the
long list of mysteries surrounding superconductivity, providing evidence that
the new materials, which scientists are calling "doped rare earth iron
oxyarsenides," develop superconductivity in quite a new way, as detailed in the
latest issue of the prestigious journal Nature.
Though research on this substance is very much in its early stages, scientists
are talking excitedly of "promise" and "potential."
The National High Magnetic Field Laboratory's 45-tesla Hybrid
magnet, which produces the highest field of any continuous field magnet in the
world, was used to measure how high a magnetic field the new superconducting
material could tolerate.
"What one would like is a greater
selection of superconductors, operating at higher temperatures, being cheaper,
possibly being more capable of being made into round wires," said Larbalestier,
director of the ASC. "Iron and arsenic, both inherently cheap materials, are key
constituents of this totally new class of superconductors. We're just
fascinated. It's superconductivity in places you never thought of."
Superconductivity can be thought of as "frictionless" electricity. In
conventional electricity, heat is generated by friction as electrons (electric
charge carriers) collide with atoms and impurities in the wire. This heating
effect is good for appliances such as toasters or irons, but not so good for
most other applications that use electricity. In superconductors, however,
electrons glide unimpeded between atoms without friction. If scientists and
engineers ever harness this phenomenon at or near room temperature in a
practical way, untold billions of dollars could be saved on energy costs.
That's a big if. Superconductivity, though promising, is still impractical in
routine engineering use because it requires a very cold environment attainable
only with the help of expensive cryogens such as liquid helium or liquid
nitrogen. Past discoveries have helped scientists inch their way up the
thermometer, from superconductors requiring minus 452 degrees Fahrenheit (or 4.2
Kelvin) to newer materials that superconduct at around minus 200 degrees F (138
K) — still frigid, but substantially warmer and more practical.
Early this year, Japanese scientists who had been developing iron-based
superconducting compounds for several years finally tweaked the recipe just
right with a pinch of arsenic. The result: a superconductor, also featuring
oxygen and the rare earth element lanthanum, performing at a promising minus 413
degrees F (26 K). The presence of iron in the material was another scientific
stunner: Because it's ferromagnetic, iron stays magnetized after exposure to a
magnetic field, and any current generates such a field. As a rule, magnetism's
effect on superconductivity is not to enhance it, but to kill it.
Teams of scientists quickly got busy synthesizing and studying various iron
oxyarsenides. Larbalestier, eager to get in on the research, secured a sample
from colleagues at Oak Ridge. His objective: Put it in the magnet lab's 45-tesla
Hybrid magnet to see how high a magnetic field the new material could tolerate.
(Tesla is a unit of magnetic field strength; the Earth's magnetic field is one
twenty thousandth of a tesla.)
Hunte and his colleagues thought the world-record Hybrid magnet would be more
than sufficient to test the field tolerance limits of the new material. They
thought wrong: The iron oxyarsenide kept superconducting all the way up to 45
tesla, far past the point at which other superconductors become normal
A high tolerance for magnetic field is one of three key properties researchers
hope for in superconductors. Also desirable are the abilities to operate at
relatively high temperatures and in the presence of high electrical currents.
Superconductors are used to make MRI and research magnets, and now they are
being tested in a new generation of superconducting electric motors, generators,
transformers and power transmission lines. Today, the most powerful
superconducting magnet generates a field of about 26 tesla. If a superconductor
could be found that tolerates a higher current and field, it may make possible
more powerful magnets, opening up vast new research areas to scientists and
Hunte's experiment yielded other tantalizing findings. Although scientists
discovered half a century ago that superconducting electrons enter the "Cooper
pair" state, pairing with opposite spin and momentum, magnetism was always
thought to break such pairs. Now the archetypal magnetic atom, iron, is a key
part of this new class of high temperature superconductors. Scientists have yet
another puzzle to probe.
"So far," said Hunte, "based on both theoretical calculations and what we're
seeing from the experiments, it seems likely that this is a completely different
mechanism for superconductivity."
Hunte is quick to say the group's research barely scratches the surface.
"The field is completely open. No one knows where this is going to go," Hunte
said. "If it's found that these materials can support high current densities,
then they could be tremendously useful."
The National High Magnetic Field Laboratory develops and operates
state-of-the-art, high-magnetic-field facilities that faculty and visiting
scientists and engineers use for research. The laboratory, which is operated by
a consortium composed of Florida State University, the University of Florida and
Los Alamos National Laboratory, is sponsored by the National Science Foundation
and the state of Florida. To learn more, visit
Florida State University
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