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MMM 2022

November 07, 2022

Minneapolis, United States

Role of Aggregation Dynamics in Magneto Optical Scattering by Superparamagnetic Nanoparticles

Superparamagnetic nanoparticles (SNPs) are widely used in biomedical applications like imaging, magnetic hyperthermia, drug delivery, etc. 1-2. We present a continuation of our study of the scattering of dilute aqueous suspensions of single-domain magnetite nanoparticles using an AC Faraday rotation setup 3-5. The setup employs a stabilized He-Ne laser (633 nm) along with an AC magnetic field (130-1120 Hz) that enables lock-in detection. We have measured the scattering response of magnetite nanoparticles that vary in diameter from 15 to 25 nm. Our previous results analysed the scattering of light by SNPs subjected to an AC magnetic field, utilizing the even harmonics of the intensity signal. In this study, we continue to investigate the leading even harmonic (2f) signal to analyse scattering, but with added emphasis on the initial polarization angle of the incident light (linearly polarized) and its relationship to the orientation of the applied magnetic field. This approach allows us to investigate how the direction of the applied magnetic field results in a shape anisotropy for the SNP aggregates, and the effect that this anisotropy has on the scattering of light with varying angles of incident polarization. Differences in scattering are then related to the structural details of the aggregates as well as the time dynamics of the formation of these structures. The two orthogonal cases (transverse and longitudinal) that form the basis of this analysis are where incident polarization is perpendicular and parallel to the applied field (also the presumed long axis of aggregates), respectively. The scattering is also measured for various other angles between a parallel and perpendicular orientation. The model allows us to predict an angle for which the scattering is not affected by the application of the magnetic field. We show that the presence of this angle is confirmed by our data. Our results provide important insight into the role of nanoparticle size (core and hydrodynamic), particle concentration, and magnetic field profile (intensity and frequency) in the formation dynamics of clusters.


  1. R. Hergt, S. Dutz, and M. Zeisberger, Nanotechnology, 21, (2010).
  2. Y. Xiao and J. Du, J. Mater. Chem. B, 8, 3, 354–367, (2020).
  3. S. Vandendriessche, W. Brullot, D. Slavov, V. Valev, and T. Verbiest, Appl. Phys. Lett., 102, (2013).
  4. C. Patterson, M. Syed, Y. Takemaura, Journal of Magnetism and Magnetic Materials, 451, 248-253
  5. M. Syed, W. Li, N. Fried, and C. Patterson, AIP Advances, 11, 015328 (2021).

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