Explain Curie's law.

Explanation

Experimentally it was found that the magnetisation of a paramagnetic material is inversely proportional to the absolute temperature T.
Curie experienced that magnetization of paramagnetic substance is directly proportional to external magnetic field `B_0` and inversely proportional to absolute room temperature.
`therefore M= C(B_0)/( T) " "...(1) and M= chi H " "...(2)`
and `B_0 = mu_0 H`
`therefore M= (Cmu_0 H)/(T)`
`therefore (M)/( H) = (C mu_0 )/( T)`
`therefore chi = (Cmu_0)/( T) ` [From equation (2) ]
This is known as Curie.s law. The constant C is called Curie.s constant.
For a paramagnetic material both `chi and mu_r` depend not only on the material but also on the absolute temperature.
As the field `(B_0)` is increased or the temperature is lowered the magnetisation increases until it reaches the saturation value `M_S` at which point all the dipoles are perfectly aligned with the field. Beyond this, Curie.s law is no longer valid.