magnetism
magnetism Properties of matter and of electric currents associated with a field of force (magnetic field) and with a north-south polarity (magnetic poles). All substances possess these properties because orbiting electrons in their atoms produce a magnetic field; similarly, an external magnetic field affects the electron orbits. All substances possess weak magnetic (diamagnetic) properties and tend to align themselves with the field, but in some cases this diamagnetism is masked by the stronger forms of magnetism: paramagnetism and ferromagnetism. Paramagnetism is caused by electron spin, and occurs in substances having unpaired electrons in their atoms or molecules. The most important form of magnetism, ferromagnetism, is shown by substances such as iron and nickel, which can be magnetized by even a weak field due to the formation of tiny regions, called domains, that behave like miniature magnets and align themselves with an external field. In 1864, Scottish physicist James Clerk Maxwell produced a unified mathematical theory of electricity and magnetism (electromagnetism). The scientific branch concerned with the magnetic properties of the Earth is called geomagnetism.
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magnetism
