= Magnetic moment inferred from an entropy derivative
{title2=$m(T,B)=\alpha B/T+m_0(B)$}
With magnetic <Helmholtz free energy> convention $dF=-S\,dT-m\,dB$, a measured $(\partial S/\partial B)_T=-\alpha B/T^2$ fixes $(\partial m/\partial T)_B$ to the same value. Integrating determines the displayed inverse-temperature term but leaves a temperature-independent function $m_0(B)$. An independent constitutive or boundary condition is needed to fix it. Requiring zero moment at infinite <temperature> recovers <Curie's law> without that offset.
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