A magnetic field characterized by its own north and south magnetic poles separated by a finite distance.

The dipole field is a field pattern produced by a closely spaced positive and negative electric charge or a north and south magnetic pole. At distances large compared to the dipole length, the field falls off as the third power of the distance away from the charges or poles producing it.

North and south magnetic poles separated by a finite distance. An electric current loop, including the effective current of a spinning nucleon or nucleus, can create an equivalent magnetic dipole.

Interaction between a spin and its neighbors due to their magnetic dipole moments. This is an important mechanism contributing to relaxation rates. In solids and viscous liquids this can result in broadening of the spectral lines.

Magnetic forces are fundamental forces that arise due to the movement of electrical charge. Maxwell's equations describe the origin and behavior of the fields that govern these forces. Thus, magnetism is seen whenever electrically charged particles are in motion. This can arise either from movement of electrons in an electric current, resulting in 'electromagnetism', or from the quantum-mechanical orbital motion (there is no orbital motion of electrons around the nucleus like planets around the sun, but there is an 'effective electron velocity') and spin of electrons, resulting in what are known as 'permanent magnets'.
The physical cause of the magnetism of objects, as distinct from electrical currents, is the atomic magnetic dipole. Magnetic dipoles, or magnetic moments, result on the atomic scale from the two kinds of movement of electrons. The first is the orbital motion of the electron around the nucleus this motion can be considered as a current loop, resulting in an orbital dipole magnetic moment along the axis of the nucleus. The second, much stronger, source of electronic magnetic moment is due to a quantum mechanical property called the spin dipole magnetic moment.
Gauss (G) and tesla (T) are units to define the intensity of magnetic fields. One tesla is equivalent to 10 000 gauss.
Typically, the field strength of MRI scanners is between 0.15 T and 3 T.

See also Diamagnetism, Paramagnetism, Superparamagnetism, and Ferromagnetism.