An object may be magnetized by placing it in magnetic field of strength H. The magnetic susceptibity χm is defined as-


The relative permeability is related to the magnetic susceptibilty via

The magnetic flux density B is then due to the external magnetic field H and the magnetized field of the object M

In a diamagnetic substance the χm is small and negative (~ -10-5). In a paramagnetic substance it is small (~ 10-3) and positive while in a ferromagnetic substance it is much larger (~ 106) and positive.

Note, the magnetization M does not always respond linearly to the applied magnetic field H. In such cases, the magnetic susceptiblity can be defined by the slope dM/dH or by some other approximation.

Note, the magnetic susceptibility does not have units.

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