FIG. 2.

Measured and calculated ratios of the fifth to third harmonics as a function of the scaled frequency Ω = ωτ_B for the “$100\mathrm{nm}$” iron oxide particles in the glycerol–water ferrofluids. The measured values are for a range of viscosities and are from Weaver and Kuehlert (Ref. ⁷). They are scaled as a function of ωτ_B—a valid scaling law as demonstrated in the experiment with varying values of the viscosity η. The calculated curves assume $T=293\mathrm{K}$, $\eta =1.0049\mathrm{mPa}\text{-}\mathrm{s}$, $B_0=10\mathrm{mT}$, $R=65.5\mathrm{nm}$, and $m_0=9.42\times {10}^{-18}\mathrm{A}{\mathrm{m}}^2$. For the polydisperse case β = 80 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).