 Curie constant

The Curie constant is the coefficient $C$ in Curie's law $\chi =C/T$ for an appropriate dilute or high-temperature paramagnet. It sets the strength of the weak-field magnetic susceptibility, rather than an ordering temperature. In an SI volume-susceptibility convention for number density $n$ of identical noninteracting moments,Here ${\mu }_{\mathrm{eff}}$ is the effective magnetic moment and ${\mu }_0$ the vacuum permeability. A mole-based susceptibility uses a correspondingly mole-based constant.

Plotting magnetic susceptibility against inverse temperature can estimate $C$ in the linear weak-field regime. Exchange interactions or thermal occupation of additional levels can change the dependence, so a fitted $C$ is meaningful only with its range and normalization stated. The factor $1/3$ reflects orientational averaging in the isotropic moment model; an anisotropic response requires more information than one scalar constant.