Magnetization Dynamics and Energy Dissipation of Interacting Magnetic Nanoparticles in Alternating Magnetic Fields with and without a Static Bias Field

The effect of interparticle interactions on the magnetization dynamics and energy dissipation rates of spherical single-domain magnetically blocked nanoparticles in static and alternating magnetic fields (AMFs) was studied using Brownian dynamics simulations. For the case of an applied static magnetic field, simulation results suggest that the effective magnetic diameter of interacting nanoparticles determined by fitting the equilibrium magnetization of the particles to the Langevin function differs from the actual magnetic diameter used in the simulations. Parametrically, magnetorelaxometry was studied in simulations where a static magnetic field was suddenly applied or suppressed for various strengths of magnetic interactions. The results show that strong magnetic interactions result in longer chain-like particle aggregates and eventually longer characteristic relaxation time of the particles. For the case of applied AMF with and without a static bias magnetic field, the magnetic response of interacting nanoparticles was analyzed in terms of the harmonic spectrum of particle magnetization and dynamic hysteresis loops, whereas the energy dissipation of the particles was studied in terms of the calculated specific absorption rate (SAR). Results suggest that the effect of magnetic interactions on the SAR varies significantly depending on the amplitude and frequency of the AMF and the intensity of the bias field. These computational studies provide insight into the role of particle–particle interactions on the performance of magnetic nanoparticles for applications in magnetic hyperthermia and magnetic particle imaging.