FIG. 3.

Measured and calculated ratios of the fifth to third harmonics for monosdisperse nanoparticles for the “$40\mathrm{nm}$” iron oxide case. The measured values are from Weaver and Kuehlert (Ref. ⁷) and are scaled as a function of ωτ—a valid scaling law as demonstrated in the experiments with different values of the viscosity η. The calculated curves assume $T=293\mathrm{K}$, $\eta =1.0049\mathrm{mPa}\text{-}\mathrm{s}$, $B_0=10\mathrm{mT}$, $R=20.5\mathrm{nm}$, and $m_0=1.31\times {10}^{-18}\mathrm{A}{\mathrm{m}}^2$. For the polydisperse case β = 200 and R refers to the average radius. The measured data from Weaver are indicated with circles, the dashed line is the harmonic ratio from the Fokker–Planck approach (monodisperse) and the solid line is the ratio from the FP approach (polydisperse).