Second harmonic generation as a probe of parametric spin wave instability processes in thin magnetic films

https://journals.aps.org/prb/abstract/10.1103/PhysRevB.106.064406

We have explored the dynamic response of in-plane magnetized thin permalloy films excited by microwave fields of high amplitudes (up to 3 Oe) at 1 GHz. The response was detected using a microstrip line by measuring the second harmonic signal generated by the dynamic components of the uniform magnetization. The data measured at ferromagnetic resonance showed the threshold effect of the Suhl parametric instability process. With the increase of the microwave power above the threshold value, the dynamic response revealed an intricate nonlinear behavior, including the emergence of an additional threshold. This second threshold can be explained in terms of the "stage by stage"process of parametric spin wave excitation following the S theory of Zakharov, L'vov, and Starobinets.