Magnetism and Superconductivity
SNS should help scientists
understand how magnetic and superconducting materials
work, which could lead to improved electrical transmission,
magnets, and electronic devices. |
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High-speed
trains of the future that will be levitated by superconducting magnets will be
even faster than the TGV in France (shown here).
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Much of what is known about
the behavior of atoms in magnetic materials has been gleaned by neutron scattering.
Neutrons can reveal details about the magnetic properties of materials that cannot
be obtained by any other method. Such information has been vital to the creation
of high-density recording media such as audiotapes, videotapes, compact discs,
and computer disks.
Neutron scattering helps
scientists determine the positions and interactions of "magnetic" atoms in different
materials of importance. Because neutrons have a magnetic moment and behave as
tiny magnets, they are scattered by an interaction with the unpaired electrons
that cause magnetism in materials.
A major goal of researchers
has been to develop permanent magnets that are smaller and lighter but have more
magnetic strength per unit volume. Neutron-scattering experiments help determine
the atomic structure of high-performance magnetic materials. This information
guides industry in selecting the best materials and manufacturing processes for
magnets. Thanks to such research we can build small motors using permanent magnets
that allow us to automatically adjust our seats and open windows in cars. Compact,
lightweight magnets also increase the fuel efficiency of vehicles.
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Polarized
neutron diffraction image showing the density of magnetic electrons in a crystal
unit cell of strontium ruthenate. Neutrons unveil the structures of new magnetic
and superconducting materials. |
The SNS will provide neutrons
in a convenient energy range for studying excitations
in magnetic materials, providing more detail about
the strength of the magnetic interaction and magnetism
in metallic solids whose electrons are in bands.
The magnetic excitations in these materials often
occur at high energies and are particularly well
suited to spallation source studies. SNS will be
very useful for analyzing advanced low-dimensional
materials, including one-dimensional crystals with "magnetic atoms marching single file"
and two-dimensional structures layered as a stack of films, each a few atoms thick.
Other objects of study include materials showing the colossal magnetoresistance
effect (a large decrease in electrical resistivity that occurs when the magnetization
is aligned by an external magnetic field). A better understanding of these materials
could lead to smarter sensors and radiation-resistant computer data storage devices.
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Model of the quantum
domain state of spin and charge patterns
of a high-temperature superconductor,
as seen by neutron scattering. The colored
boxes are spins (reds up, blue down—the
size represents the magnitude of the
ordered moment). The corrugated green
represents charge modulations. |
Neutron scattering has
been valuable for studying the high-temperature superconducting materials discovered
since 1986. One unusual magnetic material of interest is yttrium-barium-copper
oxide (YBa2Cu3O7, or YBCO). If its crystalline
grains are aligned and it is chilled to liquid nitrogen temperatures, YBCO and
other similar superconductors can carry a large amount of current in a magnetic
field with no loss of energy. Neutron scattering is being used to study how magnetic
fields behave inside superconductors like YBCO. Neutron scattering allows these
fields to be seen directly, providing information that can be obtained in no other
way. This information is important in determining the current-carrying capability
of superconducting materials.
The higher-intensity SNS
should provide enough neutrons to allow scientists
to pin down the detailed role of magnetism in the
ability of material to superconduct. This information
could help scientists explain how high-temperature
superconductors work and how they are able to retain
their superconductivity at relatively high temperatures.
This understanding will lead to better superconducting
materials that can carry larger currents at higher
temperatures, making it possible to increase the
performance of high-power transmission lines and
high-field magnets. The SNS should help scientists
better understand how magnetic and superconducting
materials work and how to best assemble them—basic information that could be applied to designing faster electronic
devices.
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