Magnetic dipole moment

For a localized steady current density,It has dimensions $\mathrm{A}{\mathrm{m}}^2$.

In an external field that varies slowly across a localized magnetic dipole,

The Bohr magneton,is the natural unit of an electron's orbital and spin magnetic moment.

If $\nabla \cdot J=0$ and the current decays enough for boundary terms to vanish, thensatisfies $\nabla \cdot A=0$. Its far field is

A circular charge distribution rotating with angular speed $\omega$ can be decomposed into current loops. A hoop of line density $\eta$ and radius $R$ has $m=\pi \eta \omega R^3\hat{n}$; a disc of surface density $\sigma$ has $m=\pi \sigma \omega R^4\hat{n}/4$.