Curie's Law : For paramagnetic materials, M=CTB0 where C is the Curie's constant. The Curie constant is a material-dependent property relating a material's temperature to its magnetic susceptibility. The Curie constant, when expressed in SI units, is given by C=3kBμ0μB2Ng2J(J+1) where N is the number of magnetic atoms (or molecules) per unit volume, g is the Land g-factor, μB(9.27400915e−24J/TorAm2) is the Bohr magneton, J is the angular momentum quantum number and kB is Boltzmann's constant.
The temperature of transition from ferromagnetic to paramagnetism is called the Curie temperature Tc.
Ferromagnetic materials have large magnetic susceptibility and are characterised by non linear relation between magnetic field (B) and magnetic intensity (H).They show the property of hysteresis.