- Curie point
The Curie point (Tc), or Curie temperature, is a term in
physicsand materials science, named after Pierre Curie(1859-1906), and refers to a characteristic property of a ferromagnetic or piezoelectricmaterial.
Curie point in ferromagnetic materials
The Curie point of a ferromagnetic material is the
temperatureabove which it loses its characteristic ferromagnetic ability (768°C for iron). At temperatures below the Curie point the magnetic moments are partially aligned within magnetic domains 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
hysteresiscurve with the applied field strength. The destruction of magnetization at the Curie temperature is a second-order phase transitionand a critical point where the magnetic susceptibilityis theoretically infinite.
One application of this effect is in
magneto-opticalstorage media, where it is used for erasing and writing of new data. Famous examples include the Sony Minidiscformat, as well as the defunct CD-MO format.
Other uses include temperature control in
soldering irons 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
piezoelectricmaterials to describe the temperature above which the material loses its spontaneous polarization and piezoelectric characteristics. In lead zirconate titanate(PZT), the material is tetragonal below Tc and the unit cell contains a displaced central cationand hence a net dipole 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.
ferromagnetismfor a list of ferromagnetic materials and their Curie temperatures.
* [http://es.youtube.com/watch?v=X8ZHQQUusGo Ferromagnetic Curie Point] . Video by
Walter Lewin, M.I.T.
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