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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 51: Complex Fluids and Soft Matter (joint session DY/CPP)
CPP 51.4: Vortrag
Freitag, 22. März 2024, 10:15–10:30, BH-N 243
Stochastic rotational dynamics of strongly coupled superparamagnetic particles — •Andrey Kuznetsov1, Sofia Kantorovich1, Vladimir Zverev2, and Ekaterina Elfimova2 — 1University of Vienna, Vienna, Austria — 2Ekaterinburg, Russia
We report a theoretical study of the rotational dynamics of interacting superparamagnetic nanoparticles in time-varying magnetic fields. The research is motivated by an increasing interest in biomedical applications of magnetic nanoparticles (such as cancer hyperthermia or magnetic particle imaging). We consider an ensemble of spherical single-domain particles with a uniaxial crystallographic anisotropy. Particles are uniformly distributed in a 3D space, while their easy axes are either co-aligned or distributed at random. We develop a mean-field approach that allows one to describe the dynamics of the system magnetization under oscillating field of arbitrary frequency and magnitude. To test the validity of the theory, its predictions are compared to Langevin dynamics simulations. It is shown, that if the energy of dipolar interactions is comparable to the energy of thermal fluctuations, the theory works well in wide ranges of particle concentrations and anisotropy constants. However, at lower temperatures the agreement breaks down. In particular, for isotropic nanoparticles our theory predicts a Debye-like susceptibility spectrum with a single relaxation time. In simulations we instead observe an emergence of a uniform band of relaxation times, that broadens with the increase of dipolar coupling parameter.
Keywords: magnetic nanoparticles; dipole-dipole interactions; dynamic mean-field theory; Fokker-Planck Equation; Langevin dynamics