We show that in the severe slowing down temperature regime the relaxation of antiferromagnetic rings and similar magnetic nanoclusters is governed by the quasi-continuum portion of their quadrupolar fluctuation spectrum and not by the lowest excitati
on lines. This is at the heart of the intriguing near-universal power-law temperature dependence of the electronic correlation frequency $omega_c$ with an exponent close to 4. The onset of this behavior is defined by an energy scale which is fixed by the lowest spin gap $Delta_0$. This explains why experimental curves of $omega_c$ for different cluster sizes and spins nearly coincide when $T$ is rescaled by $Delta_0$.
