where C is a material-specific Curie constant, T is absolute temperature, measured in kelvin, 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.
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 γ. However, at temperatures T ≫ Tc the expression of the Curie–Weiss law still holds, but with Tc replaced by a temperature Θ that is somewhat higher than the actual Curie temperature. Some authors call Θ the Weiss constant to distinguish it from the temperature of the actual Curie point.
The Curie-Weiss Law is an adapted version of Curie's Law, which for a paramagnetic material is
For the Curie-Weiss Law the total magnetic field is B+λM where λ is the Weiss molecular field constant and then
which can be rearranged to get
which is the Curie-Weiss Law
where the Curie Temperature TC is
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- Hall, J.R. Hook, H.E. (1994). Solid state physics (2nd ed.). Chichester: Wiley. ISBN 0471928054.
- Levy, Robert A (1968). Principles of Solid State Physics. Academic Press. ISBN 978-0124457508.