Independent-spin magnetic moment
= Independent-spin magnetic moment
{title2=$\mu_{\rm eff}^2=4\mu_B^2\sum_i S_i(S_i+1)$}
For uncoupled centres with approximately equal $g=2$, squared <magnetic moments> add: $\mu_{\rm eff}/\mu_B=2\sqrt{\sum_i S_i(S_i+1)}$. This does not assume that the individual <spins> add to a definite total <spin>; appreciable <exchange interaction> invalidates the independent-centre approximation.