Magnetization

Magnetization (symbol M, or Hi) is a process by which magnetic properties are conferred on a body. It is obtained by orienting the magnetic dipoles of the atomic structure thanks to an external magnetic field; its quantification is established by the intensity of magnetization, a vector quantity that represents the magnetic moment of the volume unit of the body. For a given material, the magnetization varies with the intensity of the magnetizing field and the temperature.

In electromagnetism, magnetization is the vector field that expresses the density of permanent or induced magnetic dipole moments in a magnetic material.

where μ0 is the magnetic permeability of the vacuum and B is the magnetic induction in the material. The magnetic field is modified by polarization effects due to the atomic nature of matter and, as happens for the electric polarization in the presence of an electric field, it is possible to use this model to describe the behavior of the magnetic field in materials subject to polarization, which they are divided into three categories: diamagnetic, paramagnetic and ferromagnetic. Movement within this field is described by direction and is either Axial or Diametric.

The origin of the magnetic moments responsible for magnetization can be either microscopic electric currents resulting from the motion of electrons in atoms, or the spin of the electrons or the nuclei. Net magnetization results from the response of a material to an external magnetic field.

  • Paramagnetic materials have a weak induced magnetization in a magnetic field, which disappears when the magnetic field is removed.
  • Ferromagnetic and ferrimagnetic materials have strong magnetization in a magnetic field, and can be magnetized to have magnetization in the absence of an external field, becoming a permanent magnet.

Magnetization is not necessarily uniform within a material, but may vary between different points. Magnetization also describes how a material responds to an applied magnetic field as well as the way the material changes the magnetic field, and can be used to calculate the forces that result from those interactions. It can be compared to electric polarization, which is the measure of the corresponding response of a material to an electric field in electrostatics.

The magnetic properties of a material are explained, on a theoretical level, by Ampère’s equivalence theorem, formulated by the scientist of the same name in 1820. The theorem states that a coil crossed by an electric current behaves, at a great distance, like a magnetic dipole.

Taking advantage of the planetary model of the atom, the electrons inside the matter orbit around the atomic nucleus generating the characteristic magnetic field of the coil. Each electron therefore constitutes a microscopic coil, crossed by a current called Amperian current, which in the absence of external electromagnetic fields is randomly oriented. The presence of a local magnetic field involves a collective polarization of the coils, mainly caused by their orientation, which at a macroscopic level results in the modification of Maxwell’s equations.

Exploiting the planetary model of atom, electrons inside the matter orbit around the atomic nucleus generating the magnetic field characteristic of the loop. Each electron constitutes a microscopic loop, crossed by a current called amperian current, that in absence of external electromagnetic field is randomly oriented. The presence of a local magnetic field involves a collective polarization of the coils, mainly caused by their orientation, which at macroscopic level results in the modification of Maxwell’s equations.

Related keywords

  • Demagnetization (degaussing)

Bibliography

  1. C.A. Gonano; R.E. Zich; M. Mussetta (2015). “Definition for Polarization P and Magnetization M Fully Consistent with Maxwell’s Equations” (PDF). Progress in Electromagnetics Research B64: 83–101. doi:10.2528/PIERB15100606.