What is magnetic moment of a bar magnet

1. When a bar magnet of pole strength (m) and length (2l) is suspended freely in air,it always turns along the magnetic north (N) and South poles (S) of the earth.

2. This is because the bar-magnet is acted upon by 'a' couple constituted by two parallel forces separated by a distance 2l equal to the length of the magnet.

3. Magnetic moment (M) of a bar-magnet is measured by the product of its pole- strength (m) and its magnetic length (2l)  i.e M=2l

4. Units : Ampere-metre2 (A-m²)