Curie–Weiss law

(electromagnetism) A relation between magnetic or electric susceptibilities and the absolute temperatures which is followed by ferromagnets, antiferromagnets, nonpolar ferroelectrics, antiferroelectrics, and some paramagnets.

A relation between magnetic or electric susceptibilities and the absolute temperature which is followed by ferromagnets, antiferromagnets, nonpolar ferroelectrics and antiferroelectrics, and some paramagnets. The Curie-Weiss law is usually written as the equation below, where χ is the susceptibility, C is a constant for each material, T is the absolute temperature, and θ is called the Curie temperature. Antiferromagnets and antiferroelectrics have a negative Curie temperature. The Curie-Weiss law refers to magnetic and electric behavior above the transition temperature of the material in question. It is not always precisely followed, and it breaks down in the region very close to the transition temperature. Often the susceptibility will behave according to a Curie-Weiss law in different temperature ranges with different values of C and θ. See also Curie temperature; Electric susceptibility; Magnetic susceptibility.

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

where

χ is the magnetic susceptibility

C is a material-specific Curie constant

T is absolute temperature, measured in kelvins

T_c is the Curie temperature, measured in kelvins

The susceptibility has a singularity at T = T_c. 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.

Some authors call this effective the Weiss constant, to distinguish it from the temperature of the actual Curie point.

See also

• Curie's law
• Paramagnetism
• Pierre Curie

References

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

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