The susceptibility has a singularity at T = Tc. At this temperature and below there exists a spontaneous magnetization.
In many materials the Curie-Weiss law fails to describe the susceptibility in the immediate vicinity of the Curie point, since it is based on a mean-field approximation. Instead, there is a critical behavior of the form
with the critical exponent . However, at temperatures the expression of the Curie-Weiss law still holds, but with representing a temperature which is somewhat higher than the actual Curie temperature.