# Magnetisation **A [[vector field]] that represents the density of magnetic dipole moments in a magnetic material.** > [!infobox] Magnetisation > | | | |:------------ | ------------:| | ***Symbol*** | $\mathbf{M}$ | | ***SI base units*** | $\text{A}\;\text{m}^{-1}$ | > [!NOTE] Magnetisation > The *magnetisation* of a region is > $\mathbf{M}=\frac{d\mathbf{m}}{dV}$ > - $\mathbf{m}$ - the *elementary magnetic dipole moment* > - $V$ - the *volume element* The *magnetisation* of a material is dependent on the number of magnetic dipole moments in a given volume which can become magnetised by an external field. These magnetic dipole moments can be tiny electric currents generated by the *motion of electrons* within atoms or the *intrinsic [[spin]]* of charged [[Elementary Particle|elementary particles]]. Intuitively, the magnetisation of a material can be thought of as the *degree to which the material responds* to an applied [[magnetic field]], similarly to how the electric polarisation of a material describes the response of a material to an external electric field. The magnetisation of a material is used in the definition of the [[Magnetic Field#The H-field|H-field]]. In a vacuum, the magnetisation is *zero* as there are no magnetic dipole moments and thus the relationship between the B and H-fields relies solely on the intrinsic magnetic permeability of a vacuum. The term "magnetisation" is also used to describe the process by which a material is magnetised to produce an induced magnetic field.