Superconductors

Superconductors are materials that, at very low temperatures, conduct electricity with no resistance.

This means that, unlike the more familiar conductors such as copper or steel, a superconductor can carry a current indefinitely without losing any energy in the form of heat, light, or sound.

Another important property is that no magnetic field can exist within a superconductor. This property has been exploited in the creation of maglev (for magnetic levitation) high-speed trains. This property is also used, paradoxically, in the creation of very strong magnets used in research and in medical applications such as magnetic resonance imaging (MRI).

Source: GrenFacts, based on Superconductor week Glossary  

Magnetism

GreenFacts Summary on Static Fields:

• 3. What are the sources of static magnetic fields?

Static Fields