Elucidation of relaxation dynamics of ferrite nanoparticles at nanosecond timescales*

Magnetic nanoparticles (MNPs) are becoming increasingly important as tracers for non-invasive, in vivo magnetic imaging (e.g. MPI¹), magnetic hyperthermia, and thermometry². For these applications, MNP tracers are driven by AC magnetic fields and detected by their modulated magnetic moments. The observed magnetization dynamics, which span broad timescales from seconds to nanoseconds³, are governed by a complex set of parameters, including size, morphology, magnetic anisotropy, saturation magnetization, and interactions.⁴ Here, we present time and frequency domain measurements for our synthesized ferrite and cobalt-doped ferrite nanoparticles suspended in solution over a range of temperatures (240-330 K), magnetic field amplitudes (0-20 mT_RMS), and frequencies (DC-50 MHz) to elucidate relaxation mechanisms and quantify magnetic monodispersity.

[1] Gleich et al. Nature, 435, p. 1214-7 (2005)

[2] Bui et al. J. Appl. Phys., 128, 224901, p. 1-9 (2020)

[3] Deissler et al. Med. Phys. 41, 012301 (2014)

[4] Anderson et al. Phys. Rev. B, 94, p. 1-8 (2016)