Reed Relays and
Electronics India Limited
Manufacturer of Reed Switches, Reed Sensors and Reed-based products
Reed Relays and Electronics India Limited Incorporated in 1971

Curie Temperature

Curie Point or Curie Temperature is the temperature above which a Ferro-magnetic material loses its Ferro-magnetism and becomes Para-magnetic. The Nicken Iron alloy used in the construction of Reed Switches tends to retain less and less magnetism as the application temperature goes up, thereby reducing contact forces and leading to a shorter operating life.

Curie Temperature (Wikipedia)

Figure 1. Below the Curie temperature, neighbouring magnetic spins align parallel to each other in ferromagnet in the absence of an applied magnetic field
Figure 2. Above the Curie temperature, the magnetic spins are randomly aligned in a paramagnet unless a magnetic field is applied

In physics and materials science, the Curie temperature (TC), or Curie point, is the temperature above which certain materials lose their permanent magnetic properties, to be replaced by induced magnetism. The Curie temperature is named after Pierre Curie, who showed that magnetism was lost at a critical temperature.

The force of magnetism is determined by the magnetic moment, a dipole moment within an atom which 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 a material's intrinsic magnetic moments 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, the ordered magnetic moments (ferromagnetic, Figure 1) change and become disordered (paramagnetic, Figure 2) at the Curie temperature. Higher temperatures make magnets weaker, as spontaneous magnetism only occurs below the Curie temperature. Magnetic susceptibility above the Curie temperature can be calculated from the Curie–Weiss law, which is derived from Curie's law.

In analogy 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 electric polarization that goes from a finite value to zero when the temperature is increased above the Curie temperature.

Curie temperature of materials
Material Curie
temperature (K)
Iron (Fe) 1043
Cobalt (Co) 1400
Nickel (Ni) 627
Gadolinium (Gd) 292
Dysprosium (Dy) 88
Manganese bismuthide (MnBi) 630
Manganese antimonide (MnSb) 587
Chromium(IV) oxide (CrO2) 386
Manganese arsenide (MnAs) 318
Europium oxide (EuO) 69
Iron(III) oxide (Fe2O3) 948
Iron(II,III) oxide (FeOFe2O3) 858
NiO–Fe2O3 858
CuO–Fe2O3 728
MgO–Fe2O3 713
MnO–Fe2O3 573
Yttrium iron garnet (Y3Fe5O12) 560
Neodymium magnets 583–673
Alnico 973–1133
Samarium–cobalt magnets 993–1073
Strontium ferrite 723
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