Alternating field magneto-optical response of hard magnetic nanoplate dispersions

Here we provide an analysis of alternating field magneto-optical (AFMO) response for concentrated dispersions of hard magnetic nanoplates. Dynamics of hexaferrite 50×5 nm nanoplates in 0.3–30 g/L magnetic fluids was traced with amplitude and phase shift of transmission AFMO response in the frequency range of 1 Hz – 10 kHz and magnetic fields up to 50 Oe. AFMO signal was used for reconstructing fast magnetization susceptibility dependence on the applied field depending on concentration of nanoplates. The two modes of platelets reorientation were revealed with AC field frequency and amplitude variation. High-frequency mode, characterized by magnetization phase lag, increasing with the excitation field frequency, corresponds to incomplete orientation of platelets after the field. Contrary, the low-frequency mode with magnetization phase lag, increasing reciprocally to the excitation field frequency, reveals AC coercivity of ferrofluid. The last is addressed to the self-stabilization of particles orientations by magnetic momenta of constituent particles.

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