Study and optimization on hyperthermia performance of magnetic fluids modeled by coupled Brownian–Néel rotations

Superparamagnetic nanoparticles (SMNPs) with nonlinear magnetic behavior under alternating magnetic fields hold great potential in biomedical applications, including magnetic hyperthermia, biosensing, magnetic separation, magnetic particle imaging, etc. Magnetic hyperthermia therapy, based on the relaxation movement of SMNPs subjected to an alternating magnetic field, is a promising modality for tumor treatment. Herein, we applied the stochastic Langevin equation to study the magnetic hyperthermia performance of SMNPs by taking the coupled Brownian–Néel rotations into account. The specific absorption rate (SAR) of magnetic fluids is used as a parameter for optimizing the amplitude and frequency of alternating magnetic fields and guiding the design of SMNPs. Specifically, by accounting for the dipole–dipole interactions between SMNPs, it is revealed that these interactions significantly suppress the relaxation behavior of particles, thereby reducing SAR. Furthermore, this study systematically examines the effects of key factors such as particle concentration, particle size, and magnetic anisotropy constant on SAR. The accurate prediction of the rotational and magnetic dynamics of SMNPs under an oscillating magnetic field provides valuable theoretical insights and technical support for the optimized design of external magnetic field systems and the precise fabrication of SMNPs.