Adaptive Properties of a Ferromagnetic Single-Domain Grain in Alternating Magnetic Fields.

A general self-consistent theory of adaptive properties of a ferromagnetic single-domain grain in alternating magnetic fields is constructed. Thresholds of new family of parametric instabilities of all orders are calculated. It is shown that the level of excitation of the magnetic moment and the phase of forced oscillations with respect to the pump field serve as a convenient tool for describing emerging nonequilibrium states. An analysis was made of the overthreshold excited state determined by third- and fourth-order nonlinear interactions in terms of deviations of the ferromagnetic moment. Adaptive nonequilibrium states describe energy flows from the pump field to the thermal bath and are characterized by non-linear damped oscillations. Near the frequency of these oscillations, the effect of mixing of weak RF signals with the microwave pump field arises, as well as the effect amplification of the RF modulation of the pump field. Using mathematical analogies, the developed theory can be transferred to other physical systems.