Stochastic Nanoscale Magnetic Dynamics Govern Multiscale Heating in Magnetic Nanoparticles

Magnetic nanoparticle heating (MNH) enables nanoscale energy delivery, yet current predictions of nonequilibrium magnetic dynamics at the single-particle level often lack quantitative experimental validation across nanoparticle regimes and field conditions. Here, we combine experimentally derived composite magnetic anisotropy with a stochastic Landau-Lifshitz-Gilbert description to quantitatively model MNH across superparamagnetic and magnetically blocked ferrimagnetic regimes. Simulations reproduce macroscale calorimetric heating measurements across broad particle sizes and field conditions while revealing how cycle-resolved stochastic magnetic switching contributes to heat generation. This approach shows how stochastic thermal fluctuations and anisotropy-governed dynamics give rise to classical hysteresis behavior at the macroscale, providing a multiscale physical framework for modeling energy dissipation in complex magnetic nanomaterials.