Dynamic Coercivity and Energy Absorption in Ensembles of Superparamagnetic Particles

Nonlinear magnetization and the ac field energy absorption in single-domain nanoparticles with superparamagnetic behavior are considered. The exact kinetic description is reduced by retaining only the essential part of the magnetic response. Simple analytical formulas delivering the dynamic coercivity and the hysteresis loop area, i.e., absorption per cycle, are obtained. The good accuracy of these expressions with respect to temperature, frequency, and amplitude of the ac field dependences is demonstrated by comparison with the full numerical solutions.