  Understanding high-field amplitude electromagnetic heat loss phenomena is of
great importance, in particular in the biomedical field, since 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 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.
Experimental hyperthermia data with distinct ferrite-based nanoparticles, as
well as third harmonic magnetization data supports the nonlinear model, which
also has implications for magnetic particle imaging and magnetic thermometry.
