Magnetic permeability

A factor, characteristic of a material, that is proportional to the magnetic induction produced in a material divided by the magnetic field strength; it is a tensor when these quantities are not parallel.

Source:Service de « Travaux publics et Services gouvernementaux Canada »

Formula

\mu =\mu _{0}\mu _{r} where \mu _{0} is the magnetic constant that is worth 4π×10-7H/m and \mu _{r} depends on the material.