Magnetic Susceptibility and Permeability

For linear magnetic media, magnetization is directly proportional to the magnetic field intensity. The constant of proportionality, a dimensionless quantity, is called magnetic susceptibility.

Diamagnets exhibit a negative low value of susceptibility that is independent of temperature. However, for paramagnets, it is small but positive, and temperature dependent.

Recall that the magnetic field over the vacuum permeability minus the magnetization is called the magnetic field intensity. Substitution of the magnetization expression gives a relationship between magnetic field, magnetic field intensity, and susceptibility for linear media.

So, the magnetic field is proportional to the magnetic field intensity. Here, the proportionality constant is called the magnetic permeability of the material.

The ratio of the material permeability to the vacuum permeability is called relative permeability. It is slightly less than unity for diamagnets, while it is slightly greater than unity for paramagnets.

The ferromagnet hysteresis causes a non-linear dependence of magnetization on the magnetic field intensity. So, the susceptibility and relative permeability values do not remain constant. However, these values are higher compared to paramagnets at any condition.