Curie Temperature

Curie temperature (or Curie point) is the critical temperature above which a ferromagnetic material loses its permanent magnetization and becomes paramagnetic. Named after Pierre Curie, who discovered the effect in 1895, it marks the phase transition in magnetic systems analogous to the critical point in the Ising model and other phase transitions.

Below the Curie temperature, thermal energy is insufficient to overcome the exchange interactions that align magnetic domains, and the material exhibits spontaneous magnetization — a macroscopic example of spontaneous symmetry breaking. Above the Curie temperature, thermal fluctuations disrupt this alignment, and the net magnetization vanishes continuously. The transition is typically second-order, with critical exponents belonging to the Ising universality class.

The Curie temperature is not merely a material property. It is a structural parameter that depends on the interaction topology of the magnetic lattice: materials with stronger exchange coupling and higher coordination numbers have higher Curie temperatures. This makes the Curie temperature a probe of the network of magnetic interactions, not merely a thermometer reading.

The Curie temperature is often treated as a material constant to be looked up in tables. This is a mistake. It is a phase transition point, and phase transition points are always properties of the interaction structure, not the individual components. A ferromagnet with the same atoms but a different lattice geometry has a different Curie temperature. The temperature is not in the atoms; it is in the topology.