Curie temperature


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Curie temperature

The critical or ordering temperature for a ferromagnetic or a ferrimagnetic material. The Curie temperature Tc is the temperature below which there is a spontaneous magnetization M in the absence of an externally applied magnetic field, and above which the material is paramagnetic. In the disordered state above the Curie temperature, thermal energy overrides any interactions between the local magnetic moments of ions. Below the Curie temperature, these interactions are predominant and cause the local moments to order or align so that there is a net spontaneous magnetization.

In the ferromagnetic case, as temperature T increases from absolute zero, the spontaneous magnetization decreases from M0, its value at T = 0. At first this occurs gradually, then with increasing rapidity until the magnetization disappears at the Curie temperature. In ferrimagnetic materials the course of magnetization with temperature may be more complicated, but the spontaneous magnetization disappears at the Curie temperature.

In antiferromagnetic materials the corresponding ordering temperature is termed the Néel temperature. Below the Néel temperature the magnetic sublattices have a spontaneous magnetization, though the net magnetization of the material is zero. Above the Néel temperature the material is paramagnetic. See Antiferromagnetism

The ordering temperatures for magnetic materials vary widely. The ordering temperature for ferroelectrics is also termed the Curie temperature, below which the material shows a spontaneous electric moment. See Ferromagnetism, Pyroelectricity

Curie temperature

[′kyu̇r·ē ‚tem·prə·chər]
(electromagnetism)
The temperature marking the transition between ferromagnetism and paramagnetism, or between the ferroelectric phase and paraelectric phase. Also known as Curie point.
References in periodicals archive ?
Hoser, "Structure of magnetite ([Fe.sub.3][O.sub.4]) above the curie temperature: a cation ordering study," Physics and Chemistry of Minerals, vol.
Such properties include saturation magnetisation, [M.sub.s], and magnetic ordering temperatures, i.e., ferromagnetic Curie temperature ([T.sub.c]) and antiferromagnetic Neel temperature ([T.sub.N]) [4].
Particularly, the high Curie temperature of AlNiCo makes it preferable for operating in harsh environment.
Aliphatic hydrocarbons dominate in the oil components at all the nine Curie temperatures, their amount increases significantly with increasing temperature.
For very low-level signals, reaching the Curie temperature is not a concern, but thermal offset voltages still can be generated by heating within the relay structure.
This change in slope occurs while crossing the Curie temperature (the temperature at which the ferromagnetic material changed to paramagnetic).
This can be explained by considering our discussion to the Curie temperature. The Curie temperature is defined as the temperature where the characteristic of thin films transform from ferroelectric to paraelectric or vice versa.
Table 1 Physical properties of gadolinium Quantity Value Curie temperature 293 K Density 7900 kg/[m.sup.3] (0.28 lb/[in.sup.3]) Heat capacity 230 J/kg x K Thermal 10.5 W/m x K conductivity Table 2 Physical properties of oxygen-freecopper Quantity Value Density 8880 kg/[m.sup.3] (0.31 lb/[in.sup.3]) Heat capacity 386 J/kg x K Thermal 398 W/m x K conductivity
These magnets are characterised by high saturation magnetisation and Curie temperature. They are more costly than other rare earth magnets but are chosen in preference to those with a lower Curie temperature.
For a normal ferroelectric above the Curie temperature, the dielectric constant follows the Curie-Weiss law:
When these objects are fired, the minerals in their clay are heated above the Curie temperature and are demagnetised.
Key words: PZT ceramics, resonance frequency, Curie temperature, coupling factor