High magnetic fields

High magnetic fields

Magnetic fields that are large enough to significantly alter the properties of objects that are placed in them. Valuable research is conducted at high magnetic fields. See Magnetism

High-field magnets

Research and development efforts in magnets and magnet materials have led to gradual increases in the fields available for scientific research to fields near 20 tesla from superconducting magnets, 33 T in copper-core (resistive) magnets, and 45 T for hybrid magnets. Superconducting magnets have the advantage that they use no electrical power once the field is established and the temperature is maintained at liquid-helium temperatures of 4.2 K (-452°F) or below. The disadvantage is that there is a critical magnetic field, Hc2, determined by the type of conductor, that limits the attainable field to about 22 T in superconducting materials currently available. Resistive magnets, which consume enormous amounts of power and are very expensive to build and operate, are confined to a few central facilities worldwide. See Superconductivity

Advanced pulsed magnets that are not self-destructing provide fields beyond 70 T for about 0.1 s. Pulsed magnets using explosive magnetic flux compression have achieved fields above 500 T for periods of 10 microseconds. See Magnet

Materials research

Research at very high magnetic fields spans a wide spectrum of experimental techniques for studies of materials. These techniques include nuclear magnetic resonance (NMR) in biological molecules utilizing the highest-field superconducting magnets, while the resistive magnet research is primarily in the investigation of semiconducting, magnetic, superconducting, and low-dimensional conducting materials.

Much of the progress in semiconductor physics and technology has come from high-field studies. For example, standard techniques for mapping the allowed electronic states (the Fermi surface) of semiconductors and metals are to measure the resistance (in the Shubnikov-de Haas effect) or magnetic susceptibility (in the de Haas-van Alphen effect) as a function of magnetic field and to observe the oscillatory behavior arising from the Landau levels of the electron orbits. Measurements at low fields are limited to low impurity concentrations since the orbits are large and impurity scattering wipes out the oscillations. At high fields of 20–200 T, the orbits are smaller, and higher impurity concentrations (higher carrier concentrations) have been studied. Another area in which very high magnetic fields have an important role is in high-temperature superconductors, which have great potential for high-field applications, from magnetic resonance imaging, to magnetically levitated trains, to basic science. See De Haas-van Alphen effect, Fermi surface, Semiconductor

Studies at high magnetic fields have played an important role in advancing understanding of magnetic materials. For example, in many organic conductors the conduction electrons (or holes) are confined to one or two dimensions, leading to very rich magnetic phase diagrams. High-field phases above 20 T include spin-density waves, a modulation of the electron magnetic moments that can propagate through the crystal, modifying the conduction and magnetic properties. Another area of interest is the magnetic levitation of diamagnetic materials (the most common materials). See Magnetic materials, Phase transitions, Spin-density wave

References in periodicals archive ?
Kazuhiro Fujita (Brookhaven National Lab.), used high magnetic fields to suppress the homogeneous superconductivity in the cuprate superconductor Bi2Sr2Ca2CuO2.
Von Klitzing's research currently focuses on the properties of low-dimensional electronic systems, typically at low temperatures and in high magnetic fields.
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It is now also possible for scientists to use high magnetic fields to exploit the magnetism of a material for controlling chemical and physical processes, which is attractive for magnetic separation and magnetic drug delivery systems (MDDS), for example.
The Omega Seamaster Aqua Terra has been tested and built to withstand even high magnetic fields.
The magnetic field loop sensor was made in Institute of High Magnetic Fields of Vilnius Gediminas Technical University (VGTU, Lithuania) and calibrated using "Lakeshore 455" gaussmeter.
You have to go to very high magnetic fields, so the engineering is very challenging, but you can get fusion in a device that's not tens of metres across, but just a few."
Nowadays cryocoolers are extensively used to cool MRI systems and magnetometers (SQUIDs) where they are continuously exposed to very high magnetic fields ~5 T or even more.
The 58 papers consider such topics as fabricating carbon-nanotube-reinforced boron carbide composite by hot-pressing following extrusion molding, the effect of pH on the microstructure and purity of copper-coated tungsten composite powders prepared by electroless plating, the in situ observation of diamagnetic fluid flow in high magnetic fields, modifying the surface of silicon carbide powder with silica coating by rotary chemical vapor deposition, and synthesizing and characterizing dense mesoporous alumina.
These materials may have an obvious role in creating temporary high magnetic fields. For example, super paramagnetic nanoparticles may have many potential uses in frofluid, color imaging, magnetic cooling (quenching), detoxification of biological fluids, controlled delivery of anti-cancer medications, MRI and magnetic cell isolation.
Utilizing high magnetic fields can enhance the spectral sensitivity of Magnetic Resonance Spectroscopy (MRS).