Magnetism and Superconductivity
High-speed trains of the future that will be levitated by superconducting magnets will be even faster than the TGV in France.
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- compact discs and computer disks.
Neutron scattering is helping scientists understand how magnetic and superconducting materials work, which could lead to improved electrical transmission, magnets, and electronic devices.
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 can 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.
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.
SNS and HFIR 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. ORNL facilities are 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.
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 also been extremely 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 capabilities available at ORNL 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.
Neutron scattering offers the promise of a much better understanding of how magnetic and superconducting materials work and how to best assemble them—basic information that could be applied to designing faster electronic devices as well as other materials that use superconductors.
