Magnetic susceptibility and permeability

Online class for complementary physics for Chemistry , S3

The ratio of magnetization (M) to magnetic field intensity (H) is a constant and in general the ratio is called magnetic susceptibility. 

It is a measure of how susceptible the material is, towards the polarization by applied field. It is characteristic of the material and is denoted by Chi (m). It is infact the volume susceptibility.

The volume susceptibility is positive for paramagnetic and negative for diamagnetic materials. In both cases, the magnitude is less than one. Susceptibility of a paramagnetic material decreases with increasing temperature as per the relationship:

Combining equation (1) with the relation connecting three magnetic vectors, we arrive at the following expression.

For diamagnetic materials, the relative permeability is slightly less than unity and for paramagnetic materials it is slightly greater than unity. Thus, for diamagnets, M and H are antiparallel (think how it is ?), and for paramagnets, M and H are parallel ( also think about this case). 

Permeability is thus the measure of the degree of penetration of magnetic field through the substance.

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