Tiny magnet with subatomic dimensions, equivalent to the flow of electric charge around a loop.
Examples include electron s circulating around atomic nuclei, rotating atomic nuclei, and single subatomic particle s with spin . On a large scale, these effects may add together, as in iron atoms, to make magnetic compass needles and bar magnets, which are macroscopic magnetic dipoles. The strength of a magnetic dipole, its magnetic moment, is a measure of its ability to turn itself into alignment with a given external magnetic field . When free to rotate, dipoles align themselves so that their moments point predominantly in the direction of the magnetic field. The SI unit for dipole moment is the ampere-square metre.