Curie temperature (or Curie point)

The Curie temperature (TC), or Curie point, is the temperature above which certain materials lose their permanent magnetic properties, which can (in most cases) be replaced by induced magnetism. In other words, the temperature at which a ferromagnetic becomes the paramagnet is called the Curie temperature. It is often mentioned in the context of remanence: above the substance-specific Curie temperature, this remanence of a ferromagnetic substance disappears. The Curie temperature indicates the temperature to which a magnet must be heated to demagnetize it.

The strength of magnetism is determined by the magnetic moment, a dipole moment within an atom that originates from the angular momentum and spin of electrons. Materials have different structures of intrinsic magnetic moments that depend on temperature; the Curie temperature is the critical point at which the intrinsic magnetic moments of a material change direction.

Permanent magnetism is caused by the alignment of magnetic moments, and induced magnetism is created when disordered magnetic moments are forced to align in an applied magnetic field. For example, ordered magnetic moments (ferromagnetic) change and become disordered (paramagnetic) at Curie temperature. Higher temperatures make magnets weaker, since spontaneous magnetism occurs only below the Curie temperature. The magnetic susceptibility above the Curie temperature can be calculated from the Curie-Weiss law, which is derived from Curie’s law.

Analogous to ferromagnetic and paramagnetic materials, the Curie temperature can also be used to describe the phase transition between ferroelectricity and paraelectricity. In this context, the order parameter is the electrical polarization, which goes from a finite value to zero when the temperature is increased above the Curie temperature.

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