- Curie temperature
In physics and materials science, the Curie temperature (Tc), 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 neighboring magnetic spins are aligned parallel within in ferromagnetic materials and anti-parallel 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.
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.
Curie temperature in ferromagnetic and ferrimagnetic materials
Given below are various Curie temperatures for different substances.
Substance Curie temp °C Iron (Fe) 770 Cobalt (Co) 1130 Nickel (Ni) 358 Iron Oxide (Fe2O3) 622
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. In lead zirconate titanate (PZT), the material is tetragonal below Tc and the unit cell contains a displaced central cation and 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.
The Curie-Weiss law
where C is a material-specific Curie constant, T is absolute temperature, measured in kelvins, and Tc is the Curie temperature, measured in kelvins.
Thus, the susceptibility approaches infinity as the temperature approaches Tc.
- Ferroelectric effect
- Curie's law
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- Pallàs-Areny, Ramon; Webster, John G (2001). Sensors and Signal Conditioning (2nd ed.). John Wiley & Sons. pp. 262–263. ISBN 978-0-471-33232-9.
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