In magnetism, the Curie–Weiss law describes the magnetic susceptibility  of a ferromagnet in the paramagnetic region above the Curie temperature:
where  is a material-specific Curie constant,  is the absolute temperature, and  is the Curie temperature, both measured in kelvin. The law predicts a singularity in the susceptibility at . Below this temperature, the ferromagnet has a spontaneous magnetization. The name is given after Pierre Curie and Pierre Weiss.