Curie constant
The Curie constant is a material-dependent property that relates a material's magnetic susceptibility to its temperature.

The Curie constant, when expressed in SI units, is given by 

,

where  is the number of magnetic atoms (or molecules) per unit volume,  is the Landé g-factor,  is the Bohr magneton,   is the angular momentum quantum number and  is Boltzmann's constant.  For a two-level system with magnetic moment , the formula reduces to

,

while the corresponding expressions in Gaussian units are
,
.

The constant is used in Curie's Law, which states that for a fixed value of a magnetic field, the magnetization of a material is (approximately) inversely proportional to temperature.

.

This equation was first derived by Pierre Curie.

Because of the relationship between magnetic susceptibility , magnetization  and applied magnetic field  is almost linear at low fields, then

,

this shows that for a paramagnetic system of non-interacting magnetic moments, magnetization  is inversely related to temperature .