Magnetic polarization is a physical quantity. It relates to the electrodynamics of macroscopic matter and characterizes the magnetic flux density of a magnetic material in a vacuum when the proportion of the magnetic field is subtracted.

Inside the ferromagnet
Ferromagnetic materials consist of many small elementary magnets, also called magnetic moments. They are largely responsible for the magnetization of a material. If they specify a direction of magnetization, one speaks of magnetic polarization. If two magnets differ by opposite north and south poles, this is called reverse polarization.

The symbol of magnetic polarization is J, the associated Unit T (Tesla). Magnetic polarization occurs when an external magnetic field is applied to a material with elementary magnets. Because the magnetic moments then add up, the external magnetic field H0 becomes around the magnetic field constant μ reinforced (corresponds to the magnetic permeability). A magnetic flux density B, which is μ larger than in a vacuum, i.e.
Ferromagnets increase the magnetic flux density. In the external magnetic field, the magnetic polarization is now due to the susceptibility χ.

How can magnetic polarization be measured?
If current flows through a coil and an iron core with a permeability greater than 1 is integrated into its interior, the magnetic flux density at the end of the coil is significantly higher than without an iron core. This is because the spins of the ferromagnetic material align themselves parallel to the external magnetic field. Due to the magnetic polarization, the magnetic flux is considerably larger - the magnetic field becomes stronger.

Because the magnetic moments of ferromagnets have a permanent alignment (due to the exchange interaction), so-called remanence occurs after switching off the external magnetic field, i.e. some of the magnetic polarization remains.