# Curie – Weiss Law

## Curie – Weiss Law

Curie Weiss law is a law which states that the magnetic susceptibility is directly proportional to the ratio of the Curie constant to the change in the temperature. It is one of the important law in electromagnetism that says that the magnetic susceptibility is above the Curie temperature point of a ferromagnetic in the paramagnetic. The magnetic moment is a quantity of a magnet that determines its torque in an external magnetic field. For example a bar magnet, electric current loop, a molecule and an electron all have a magnetic moments.

The magnetic polarization or a magnetization of a magnetic material express the density of induced or permanent magnetic moments in the vector field. The magnetic moment can develop from the microscopic electric current that is generated by the spin of the electrons or motion of electrons in an atom or the spin of the nuclei.

X = C/ (T – Tc)

Here,

C = Material specific Curie constant,

T = Absolute temperature,

Tc = Curie temperature.

The law predicts a singularity in the susceptibility at T = Tc. Below this temperature the ferromagnet has a spontaneous magnetization.

The net magnetization depends on the response of external magnetic field materials. However, they may be even present in the absence of the external magnetic field for example in a cold iron as a spontaneous magnetization. Well, other materials that have similar property are magnetite and nickel, these are called ferromagnets. The temperature which a ferromagnetic material is called Curie temperature.

Curie – Weiss Law Limitation: The Curie-Weiss law holds false in many materials to describe the susceptibility. Instead, there is a critical behaviour of the form.

X = 1/ (T – Tc)γ

At temperature T >> Tc the expression of the law still holds true. But, with the Tc will be replaced by temperature (θ) is higher than the Curie temperature.