Nanoscale Mapping of Internal Magnetization Dynamics Reveals How Disorder Shapes Heat Generation in Magnetic Particle Hyperthermia

Magnetic particle hyperthermia relies on the efficient conversion of magnetic field energy into heat, yet the microscopic mechanisms governing this process within individual particles remain poorly understood. Here, we combine AC magnetometry experiments with dynamic micromagnetic simulations to connect microstructural features, magnetization dynamics, and macroscopic heat dissipation. We resolve heat generation at the intraparticle level, uncovering heterogeneous nanoscale heat-generation bursts with nanometer and nanosecond resolution. At a given particle size, grain size acts as an experimentally tunable parameter, balancing anisotropy disorder and pinning strength, thereby controlling both the magnitude and spatiotemporal distribution of heat release. Experiments show that flux-closure-dominated nanoflower architectures composed by larger grains generate more heat than their smaller-grain counterparts, whose deeper intraparticle pinning landscape redistributes heat generation over extended time windows. Together, our results provide a mechanistic framework linking nanoparticle microstructure to magnetic heating and establish design principles for optimizing nanoflowers as magnetic hyperthermia transducers.