Giant-spin nonlinear response theory of magnetic nanoparticle hyperthermia: A field dependence study

Understanding high-field amplitude electromagnetic heat loss phenomena is of great importance, in particular, in the biomedical field, because the heat-delivery treatment plans might rely on analytical models that are only valid at low field amplitudes. Here, we develop a nonlinear response model valid for single-domain nanoparticles of larger particle sizes and higher field amplitudes in comparison to the linear response theory. A nonlinear magnetization expression and a generalized heat loss power equation are obtained and compared with the exact solution of the stochastic Landau-Lifshitz-Gilbert equation assuming the giant-spin hypothesis. The model is valid within the hyperthermia therapeutic window and predicts a shift of optimum particle size and distinct heat loss field amplitude exponents, which is often obtained experimentally using a phenomenological allometric function. Experimental hyperthermia data with distinct ferrite-based nanoparticles and third harmonic magnetization data support the nonlinear model, which also has implications for magnetic particle imaging and magnetic thermometry. Published by AIP Publishing.