= Solution
At greater concentration, the mean separation falls and the independent-moment approximation can fail. The <magnetic dipole interaction> has characteristic scale
$$
E_{\rm dd}\sim\frac{\mu_0\mu^2}{4\pi r^3},
$$
with sign and angular dependence set by moment orientation. Correlated clusters, chains or frustrated arrangements change local fields and relaxation barriers.
A plausible example is a progressively less reversible loop with larger <remanence>/<magnetic coercivity> when interactions slow collective relaxation; the figure illustrates that case. \b[The trend is not universal:] some arrangements reduce susceptibility or suppress <remanence>, and aggregation can introduce a different response from a uniform concentrated dispersion. Neither loop area nor <magnetic coercivity> must vary monotonically with concentration.
At the actual drive <frequency>, the dissipated <energy> per cycle per unit <volume> is proportional to $\mu_0\oint H\,dM$. Measure this dynamic loop rather than inferring dissipation from an unrelated slow sweep. Compare equal magnetic-material amounts, inspect dispersion state, and vary <frequency> to separate concentration-driven interactions from simple signal scaling. No biological efficacy is inferred.
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