# Dictionary:Magnetic susceptibility

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A measure of the degree to which a substance may be magnetized; the ratio k or k′ of the magnetization M or I to the magnetizing force H that is responsible for it:

FIG. M-1. Magnetic quantities and units. See also Appendix A, SI units.
${\displaystyle kH=M\;\qquad in\;the\;SI\;System,}$

${\displaystyle k'H=I\;\qquad in\;the\;cgs\;System,}$

The susceptibility is dimensionless but of different magnitude in the two systems:

${\displaystyle k=4\pi k'}$

The susceptibility is related to the magnetic permeability μ

${\displaystyle k=\mu -1\;,}$

${\displaystyle k'={\frac {\mu -1}{4\pi }}\;.}$

Susceptibility in cgs units is sometimes measured in units of 10–6 (‘‘micro-cgs’’). Rock susceptibility usually ranges from 0 to 0.01 cgs units (0 to 10 000 micro-cgs) and it is often proportional to the fraction of magnetite present. See Figure M-1.