In an atom, electron revolves around the nucleus in a closed orbit. Since electron is a charged particle, so its orbit around the nucleus is equivalent to a current loop. When electron revolves in anticlockwise direction, the current is clockwise. Thus, upper face of the electron loop acts as south pole and lower face acts as north pole. Thus an atom behaves like a magnetic dipole.
Reference: This article is referred from my book “electrical engineering materials” having ISBN 978-81-272-5069-0
Magnetic dipole moment is defined as the product of pole strength and the distance between the two poles.
Let a → distance between the poles also called magnetic length,
and m → strength of each pole.
Thus, magnetic dipole moment, pm is given as
pm = ma
pm is vector quantity directed from south to north pole.
S.I units of pm are joule/tesla or ampere metre2.
Magnetic dipole consists of two equal and opposite magnetic poles separated by a small distance.
When it is placed in an external magnetic field, it experiences a torque and dipole sets itself in a particular direction.
Example: A compass needle, a bar magnet, a current carrying loop. An atom of a magnetic material also behaves as a dipole due to electrons revolving around the nucleus.
Reference: This article is referred from my authored book”electrical engineering materials.