- Curie point
The Curie point (Tc), or Curie temperature, is a term in
physics andmaterials science , named afterPierre Curie (1859-1906), and refers to a characteristic property of aferromagnet ic orpiezoelectric material.Curie point in ferromagnetic materials
The Curie point of a ferromagnetic material is the
temperature above which it loses its characteristic ferromagnetic ability (768°C for iron). At temperatures below the Curie point themagnetic moment s are partially aligned withinmagnetic domain s in ferromagnetic materials. As the temperature is increased towards the Curie point, the alignment (magnetization) within each domain decreases. Above the Curie point, the material is purely paramagnetic and there are no magnetized domains of aligned moments.At temperatures above 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-orderphase transition and a critical point where themagnetic susceptibility is theoretically infinite.One application of this effect is in
magneto-optical storage media, where it is used for erasing and writing of new data. Famous examples include theSony Minidisc format, as well as the defunct CD-MO format.Other uses include temperature control in
soldering iron s such as the Weller WTCPT and, in general, where a temperature-controlled magnetization is desirable.Curie temperature in piezoelectric materials
In analogy to ferromagnetic materials, the Curie temperature is also used in
piezoelectric materials to describe the temperature above which the material loses its spontaneous polarization and piezoelectric characteristics. Inlead zirconate titanate (PZT), the material is tetragonal below Tc and the unit cell contains a displaced centralcation and hence a netdipole moment . Above Tc, the material is cubic and the central cation is no longer displaced from the centre of the unit cell. Hence, there is no net dipole moment and no spontaneous polarization.Curie-Weiss law
ee also
*See
ferromagnetism for a list of ferromagnetic materials and their Curie temperatures.
*Ferroelectric effect
*Néel temperature External links
* [http://es.youtube.com/watch?v=X8ZHQQUusGo Ferromagnetic Curie Point] . Video by
Walter Lewin ,M.I.T.
Wikimedia Foundation. 2010.