Curie–Weiss law
The Curie–Weiss law describes the magnetic susceptibility χ of a ferromagnet in the paramagnetic region above the Curie point:
where C is a material-specific Curie constant, T is absolute temperature, measured in kelvins, and Tc is the Curie temperature, measured in kelvin. The law predicts a singularity in the susceptibility at T = Tc. Below this temperature the ferromagnet has a spontaneous magnetization.