Curie–Weiss law

The Curie-Weiss law describes the magnetic susceptibility χ of a ferromagnet in the paramagnetic region above the Curie point:

$\chi = \frac{C}{T - T_{c}}$

where C is a material-specific Curie constant, T is absolute temperature, measured in kelvins, and T_c is the Curie temperature, measured in kelvins. The law predicts a singularity in the susceptibility at T = T_c. 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

$\chi \sim \frac{1}{(T - T_{c})^\gamma}$

with the critical exponent γ. However, at temperatures T >> T_c the expression of the Curie-Weiss law still holds, but with T_c 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.

See also

• Curie's law
• Paramagnetism
• Pierre Curie
• Pierre-Ernest Weiss

References

Introduction to Solid State Physics 7th ed. (1996) by Charles Kittel