Magnetic materials Curie temperature

CURIE POINT (or Curie Temperature). Ferromagnetic materials lose their permanent or spontaneous magnetization above a critical temperature (different for different substances). This critical temperature is called the Curie point. Similarly, ferroelectric materials lose their spontaneous polarization above a critical temperature. For some such materials, this lemperaLure is called the "upper Curie point." for there is also a "lower Curie point." below which the ferroelectric property disappears. See also Ferromagnetism. 

Equation (A2.5.20) is the Curie-Weiss law, and the temperature at which the magnetic susceptibility becomes infinite, is the Curie temperature. Below this temperature the substance shows spontaneous magnetization and is ferromagnetic. Nonnally the Curie temperature lies between 1 and 10 K. However, typical ferromagnetic materials like iron have very much larger values for quantum-mechanical reasons that will not be pursued here. 

Above a critical temperature Tc, the Curie temperature, a ferromagnetic material becomes paramagnetic, since thermal motion inhibits the parallel orientation of the magnetic moments. The susceptibility then follows the Curie-Weiss law with a positive value of the Weiss constant, 0 > 0 (Fig. 19.6). 

Above a temperature called the Curie temperature, Tc, all ferromagnetic materials become paramagnetic. The transition to a paramagnetic state comes about when thermal energy is greater than the magnetic interactions and causes the dipoles... 

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