Curie Temperature

In physics and materials science, the Curie temperature (T_c), or Curie point, is the temperature at which a ferromagnetic or a ferrimagnetic material becomes paramagnetic on heating; the effect is reversible. A magnet will lose its magnetism if heated above the Curie temperature. The term is also used in piezoelectric materials to refer to the temperature at which spontaneous polarization is lost on heating. An analogous temperature, the Néel temperature, is defined for antiferromagnetic materials. The Curie temperature is named after Pierre Curie.

Below the Curie temperature the magnetic spins of neighbouring atoms are aligned parallel within ferromagnetic materials and anti-parallel (as between different sub-lattices) in ferrimagnetic materials. As the temperature is increased towards the Curie point, the alignment (magnetization) within each domain decreases. Above the Curie temperature, the material is paramagnetic so that magnetic moments are in a completely disordered state.

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.

A heat-induced ferromagnetic-paramagnetic transition is used in magneto-optical storage media, for erasing and writing of new data. Famous examples include the Sony Minidisc format, as well as the now-obsolete CD-MO format. Other uses include temperature control in soldering irons, and stabilizing the magnetic field of tachometer generators against temperature variation.