Magnetism

Magnetism:
Magnetism is the phenomenon associated with the motion of electric charges,
although the study of magnets was very confused before the 19th century because
of the existence of ferromagnets, substances such as iron bar magnets which
maintain a magnetic field where no obvious electric current is present (see below).
Basic magnetism is the existence of magnetic fields which deflect moving charges
or other magnets. Similar to electric force in strength and direction, magnetic
objects are said to have `poles' (north and south, instead of positive and negative
charge). However, magnetic objects are always found in pairs, there do not exist
isolated poles in Nature.

The most common source of a magnetic field is an electric current loop. The
motion of electric charges in a pattern produces a magnetic field and its associated
magnetic force. Similarly, spinning objects, like the Earth, produce magnetic
fields, sufficient to deflect compass needles.
Today we know that permanent magnets are due to dipole charges inside the
magnet at the atomic level. A dipole charge occurs from the spin of the electron
around the nucleus of the atom. Materials (such as metals) which have incomplete
electron shells will have a net magnetic moment. If the material has a highly
ordered crystalline pattern (such as iron or nickel), then the local magnetic fields
of the atoms become coupled and the material displays a large scale bar magnet
behavior.