Curie temperature

File:Weiss domains in a ferromagnetic material.png

Curie temperature

The Curie temperature (or Curie point) is the temperature at which certain materials lose their permanent magnetism, to be replaced by induced magnetism. It is named after Pierre Curie, who discovered this phenomenon. The Curie temperature is a critical point where the magnetic properties of a material change.

Magnetic Phases

Below the Curie temperature, ferromagnetic and ferrimagnetic materials exhibit spontaneous magnetization—the magnetic moments of the atoms are aligned in a regular pattern. Above the Curie temperature, these materials become paramagnetic; the thermal energy overcomes the magnetic energy, causing the magnetic moments to become randomly oriented.

Ferromagnetism and Ferrimagnetism

In ferromagnetic materials, such as iron, nickel, and cobalt, the magnetic moments of atoms are aligned parallel to each other in regions called magnetic domains. In ferrimagnetic materials, such as magnetite, the magnetic moments of atoms are aligned in opposite directions, but the opposing moments are unequal, resulting in a net magnetic moment.

Paramagnetism

Above the Curie temperature, the material becomes paramagnetic. In this state, the magnetic moments are randomly oriented due to thermal agitation, and the material does not retain any magnetization in the absence of an external magnetic field.

Calculation of Curie Temperature

The Curie temperature can be theoretically calculated using the Weiss molecular field theory and the Heisenberg model. The Curie temperature is given by the formula:

\[ T_C = \frac{2JzS(S+1)}{3k_B} \]

where:

• \( J \) is the exchange interaction,
• \( z \) is the number of nearest neighbors,
• \( S \) is the spin quantum number,
• \( k_B \) is the Boltzmann constant.

Applications

The concept of the Curie temperature is crucial in various applications, including the design of magnetic storage devices, transformers, and electric motors. It is also important in the field of geophysics for understanding the magnetic properties of rocks and minerals.

See Also

• Magnetism
• Ferromagnetism
• Paramagnetism
• Pierre Curie
• Magnetic domain
• Weiss molecular field theory
• Heisenberg model