 # Curie-Weiss Law

The Curie-Weiss law is one of the important law in electromagnetism that says that the magnetic susceptibility is above the Curie temperature point of a ferromagnet 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.

$X = \frac{C}{T – T_{c}}$

Here,

$C$ = Material specific Curie

$T$ = Absolute temperature

${T_{c}}$ = Curie temperature

The net magnetization depends on the response of external magnetic field’s 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 behavior of the form.

$X \sim \frac{1}{\left (T – T_{c} \right )^{\gamma}}$

At temperature $T \gg T_{c}$ the expression of the law still holds true. But, with the $T_{c}$ will be replaced by temperature $\left (\theta \right )$ is higher than the Curie temperature.