From Academic Kids
The Curie point, or Curie temperature of a ferromagnetic material, is the temperature above which it loses its characteristic ferromagnetic ability to possess a net (spontaneous) magnetization in the absence of an external magnetic field.
At temperatures below the Curie point, the magnetic moments are partially aligned within magnetic domains in ferromagnetic materials. As the temperature is increased from below the Curie point, thermal fluctuations increasingly destroy this alignment, until the net magnetization becomes zero at and above the Curie point. Above the Curie point, the material is purely paramagnetic.
At temperatures below the Curie point, an applied magnetic field has a paramagnetic effect on the magnetization, but the combination of paramagnetism with ferromagnetism leads to the magnetization following a hysteresis curve with the applied field strength. The destruction of magnetization at the Curie temperature is a second-order phase transition and a critical point where the magnetic susceptibility is theoretically infinite.
See ferromagnetism for a list of ferromagnetic materials and their Curie temperatures.
The effect is used for temperature control in soldering irons.
See also: Ferroelectric effect