= Magnetic entropy deficit
{title2=$\Delta s_{\rm mag}=s_{\max}-s(T,B)$}
The <magnetic entropy deficit> is the <entropy> increase still available to independent moments as their field <polarization> is removed. For a spin-$J$ multiplet, $s_{\max}=k_B\ln(2J+1)$ and the high-temperature deficit is $k_BJ(J+1)[g\mu_BB/(k_BT)]^2/6$. Isothermal <magnetization> creates this deficit while rejecting heat to a bath. Subsequent reversible demagnetization can absorb <entropy> from a cooling load. The deficit, not the initial absolute <magnetic entropy>, measures that capacity.
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