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Curie constant
Since the derivation of the Curie law for paramagnetism by the French physicist Pierre Curie in 1896 and the further development by Pierre-Ernest Weiss (Curie-Weiss law), one can conclude the magnetic susceptibility of a substance (information on magnetizability amount of substance) from the absolute temperature. In this context, the so-called Curie constant has been developed.
What does the Curie Law say?
The Curies law can be derived from an ideal system of N particles with 1/2 spin. That means:
- The particles are thermally isolated.
- There is no spin-orbit coupling.
- There is no ligand field effect.
- There is no magnetic anisotropy.
- There is no magnetic interaction.
A magnetic field exerts a directing force on the spin of an electron (charge carrier, magnetic moment). If one applies an external magnetic field, one could assume that all spins of a substance align themselves with the external magnetic field, but this depends decisively on the temperature T. To calculate the susceptibility X_m (not to be confused with the permeability!) In the Curie law, the effects of the external magnetic field and the thermal effects must be taken into account. The Curie law for magnetism takes this place, although only weak magnetic fields and higher temperatures can be mapped:
C is the Curie constant in this case.
What is the Curie constant?
The Curie constant is composed as follows:
where:
the magnetic field constant (information about the ratio of the magnetic flux density to the magnetic field strength in the vacuum)
the particle density (number of particles N in a volume V, the curie Constant is substance-dependent)
the Boltzmann constant (energy / temperature, set to: 
- μ is the amount of the permanent magnetic dipole moment (measure of the magnitude of a magnetic moment)
Because the Curie law includes thermal factors, one speaks therefore of the so-called Curie temperature. It is therefore a substance-specific quantity which indicates from which temperature range the magnetic properties of a substance change. For example, with the Curie constant iron could be examined. The result: The attraction disappears completely above the Curie temperature.