## Magnetic Response

The response of a material to a magnetic field is quantified by two quantities: the susceptibility, , which is the variation of magnetisation, , with applied field, ,

 (3.3)

and the permeability, , the variation of magnetic induction, , with applied field,

 (3.4)

Permeability is often quoted relative to , the permeability of a vacuum or (within a high degree of accuracy) air.

The susceptibility and permeability of a material depends upon its magnetic characteristics. Table 3.1 gives an indication of how they vary with the type of material and magnetic ordering (if any) it displays.

Table 3.1: Variation of susceptibility, , and permeability, , with material and magnetic ordering.
 Material/Ordering Vacuum 0 Diamagnetic Small and negative Paramagnetic Small and positive Antiferromagnetic Small and positive Ferromagnetic Large and positive Ferrimagnetic Large and positive

Dr John Bland, 15/03/2003