The energetic equilibrium in the nonlinear ferromagnetic resonance

The equilibrium between pump and scattered energy in nonlinear ferromagnetic resonance (NFMR) occurs as a result of the following mechanisms: 1) the nonlinear decrease in magnon lifetime owing to the increase of excited levels nk, and 2) the non-linear frequency shifting of the spin waveband owing to the decrease of the average magnetization of the crystal. Both of these mechanisms tend to diminish the flow of energy into the spin system, but a comparison of the efficiencies of the two, the mechanisms shows that nonlinear frequency shifting predominates over the nonlinear dissipation. In fact, the nonlinear susceptibility of ferromagnetic crystals is determined chiefly by the nonlinear frequency shifting process. This causes the NFMR to be unstable, a result of which is confirmed experimentally.